publications

2025

1. A Single Bioorthogonal Reaction for Multiplex Cell Surface Protein Labeling

   Yang Huang, Chengyang Wu, Anjing Lu, Jingzhe Wang, Jian Liang, Han Sun, Liqing Yang, Shixiang Duan, Andrey A. Berezin, Chuanliu Wu, Bo Zhang, Yi-Lin Wu, and Yu-Hsuan Tsai

   J. Am. Chem. Soc. 2025, 147, 1612–1623. (DOI:10.1021/jacs.4c11701)

   Abs Link

   Small-molecule fluorophores are invaluable tools for fluorescence imaging. However, means for their covalent conjugation to the target proteins limit applications in multicolor imaging. Here, we identify 2-[(alkylthio)(aryl)methylene]malononitrile (TAMM) molecules reacting with 1,2-aminothiol at a labeling rate over 104 M–1 s–1 through detailed mechanistic investigation. The fast TAMM molecules and mild reaction conditions enable site-specific labeling of surface proteins in not only cell lines but also primary neurons and living mice. The combination of genetic code expansion and sequence-specific proteolytic cleavage enables selective modification of three different cell surface proteins through iterative TAMM condensation. TAMM condensation is also compatible with Cu-catalyzed azide–alkyne cycloaddition and tetrazine ligation for four-color fluorescent labeling, reaching the maximum available colors of conventional confocal microscopes. Thus, bioconjugation chemistry is no longer the limiting factor for multiplex cell surface protein imaging.

2024

1. Secondary Amine Catalysis in Enzyme Design: Broadening Protein Template Diversity through Genetic Code Expansion

   Thomas L. Williams, Irshad M. Taily, Lewis Hatton, Andrey A Berezin, Yi‐Lin Wu, Vicent Moliner, Katarzyna Świderek, Yu‐Hsuan Tsai, and Louis Y. P. Luk

   Angew. Chem. Int. Ed. 2024, 63, e202403098. (DOI:10.1002/anie.202403098)

   Abs Link

   Secondary amines, due to their reactivity, can transform protein templates into catalytically active entities, accelerating the development of artificial enzymes. However, existing methods, predominantly reliant on modified ligands or N-terminal prolines, impose significant limitations on template selection. In this study, genetic code expansion was used to break this boundary, enabling secondary amines to be incorporated into alternative proteins and positions of choice. Pyrrolysine analogues carrying different secondary amines could be incorporated into superfolder green fluorescent protein (sfGFP), multidrug-binding LmrR and nucleotide-binding dihydrofolate reductase (DHFR). Notably, the analogue containing a D-proline moiety demonstrated both proteolytic stability and catalytic activity, conferring LmrR and DHFR with the desired transfer hydrogenation activity. While the LmrR variants were confined to the biomimetic 1-benzyl-1,4-dihydronicotinamide (BNAH) as the hydride source, the optimal DHFR variant favorably used the pro-R hydride from NADPH for stereoselective reactions (e.r. up to 92 : 8), highlighting that a switch of protein template could broaden the nucleophile option for catalysis. Owing to the cofactor compatibility, the DHFR-based secondary amine catalysis could be integrated into an enzymatic recycling scheme. This established method shows substantial potential in enzyme design, applicable from studies on enzyme evolution to the development of new biocatalysts.

2. Selective Protein Degradation through Tetrazine Ligation of Genetically Incorporated Unnatural Amino Acids

   Jinghao Chen, Gaocan Dai, Shixiang Duan, Yang Huang, Yi‐Lin Wu, Zhiyong Xie, and Yu‐Hsuan Tsai

   Chem. Asian J. 2024, e202400824. (DOI:10.1002/asia.202400824)

   Abs Link

   Small molecule‐responsive tags for targeted protein degradation are valuable tools for fundamental research and drug target validation. Here, we show that genetically incorporated unnatural amino acids bearing a strained alkene or alkyne functionality can act as a minimalist tag for targeted protein degradation. Specifically, we observed the degradation of strained alkene‐ or alkyne‐containing kinases and E2 ubiquitin‐conjugating enzymes upon treatment with hydrophobic tetrazine conjugates. The extent of the induced protein degradation depends on the identity of the target protein, unnatural amino acid, and tetrazine conjugate, as well as the site of the unnatural amino acid in the target protein. Mechanistic studies revealed proteins undergo proteasomal degradation after tetrazine tethering, and the identity of tetrazine conjugates influences the dependence of ubiquitination on protein degradation. This work provides an alternative approach for targeted protein degradation and mechanistic insight, facilitating the future development of more effective targeted protein degradation strategies.

2023

1. Why does thionating a carbonyl molecule make it a better electron acceptor?

   Yi-Lin Wu and Anna I. Wright

   Phys. Chem. Chem. Phys. 2023, 25, 1342–1348. (DOI:10.1039/D2CP05186A)

   Abs Link

   The past decade has witnessed a surge of biomedical and materials applications of thiocarbonyl molecules (R2C[double bond, length as m-dash]S), such as in photodynamic therapy, organic field-effect transistors, and rechargeable batteries. The success of these applications originates from thiocarbonyl’s small optical gap in the visible region and the enhanced electron affinity compared to the carbonyl analogues (R2C[double bond, length as m-dash]O). Although these observations seem to be contrary to the implication based on a simple electronegativity consideration (2.58 for sulfur and 3.44 for oxygen), a natural bond orbital (NBO) analysis gives a straightforward explanation for the LUMO-lowering effect of C[double bond, length as m-dash]O → C[double bond, length as m-dash]S substitution. In comparison to the valence (2p)C/(2p)O interactions in C[double bond, length as m-dash]O, the higher 3p orbital of sulfur and its weaker overlap with the 2p level of carbon result in a weaker antibonding interaction in Image ID:d2cp05186a-t1.gif NBO, a prominent contributor to the LUMO. Such an analysis also provides a semi-quantitative understanding of the electronic effect of substituents on or in π-conjugation with a (thio)carbonyl functionality. The intuitive concepts uncovered here offer a simple rule to predict the electronic properties of π-conjugated molecules that incorporate heavy heteroelements and would facilitate materials development.

2. Synthesis, solid-state structure, and electrochemical properties of thienodipyrimidine-2,4,5,7-tetra(thi)ones

   Anna I. Wright, Benson M. Kariuki, and Yi-Lin Wu

   Arkivoc 2023, 202311998. (DOI:10.24820/ark.5550190.p011.998)

   • Dedicated to Professor Tien-Yau Luh on the occasion of his 76th birthday

   Abs Link

   Thienodipyrimidine-2,4,5,7-tetra(thi)ones were prepared by one-pot photocyclization from barbituric acid derivatives. The structures of these tricyclic molecules with multiple (thio)carbonyl groups were determined by NMR and single-crystal X-ray diffraction analysis, and the electrochemical properties were studied by cyclic voltammetry and DFT calculations. The solid-state structures of these molecules feature dipolar C=S (or C=O), chalcogen-bonding, and π-stacking interactions. The presence of two adjacent thiocarbonyl groups allows for a two-center three-electron (2c/3e) interaction upon oxidation, significantly lowering the oxidation potential.

3. Butterfly-Shaped Dibenz[a, j]anthracenes: Synthesis and Photophysical Properties

   Yan-Ying Wu, Yi-Lin Wu, Cheng-Lan Lin, Hung-Cheng Chen, Yao-Yuan Chuang, Chih-Hsien Chen, and Chih-Ming Chou

   Org. Lett. 2023, 25, 7763–7768. (DOI:10.1021/acs.orglett.3c02306)

   Abs Link

   A strategy for the synthesis of dibenz[a,j]anthracenes (DBAs) from cyclohexa-2,5-diene-1-carboxylic acids is presented. Our approach involves sequential C–H olefination, cycloaddition, and decarboxylative aromatization. In the key step for DBA skeleton construction, the bis-C–H olefination products, 1,3-dienes, are utilized as substrates for [4 + 2] cycloaddition with benzyne. This concise synthetic route allows for regioselective ring formation and functional group introduction. The structural features and photophysical properties of the resulting DBA molecules are discussed.

2021

1. Multiple C–H⋯anion and N–H⋯anion hydrogen bond directed two-dimensional crystalline nanosheets with precise distance control of surface charges for enhanced DNA capture

   Laicheng Zhou, Ran He, Yang Qin, Yi-Lin Wu, Li Jiang, Dong-Dong Zhou, and Ling Zhang

   Soft Matter 2021, 17, 9125–9130. (DOI:10.1039/d1sm01152a)

   Abs Link

   Utilizing combined non-covalent interactions and introducing anions as structure-directing factors to build oriented self-assembly and 2D crystalline nanosheet superstructures with precise distance control of surface charges in competitive aqueous solvents still represents a formidable challenge for supramolecular chemists. Here we report a simple, efficient, and general strategy for multiple C-H/N-HMIDLINE HORIZONTAL ELLIPSISanion hydrogen bond enhanced pi-pi interaction directed 2D oriented self-assembly in water, which is based on the head-to-tail association of perylene monoimide dimers (PMIs) by directing N-HMIDLINE HORIZONTAL ELLIPSISanion interactions to position the anions to the C-H of pi systems (PMIs). Interesting, this behavior only occurs for size-matched anions (Cl- to NO3-; \textless45 angstrom(3)), while larger anions could not form 2D crystalline nanosheet superstructures. The results show that crystalline nanosheet superstructures with precise distance control of surface charges can effectively capture DNA, possibly due to their high surface charge density and the distance match between the distance of surface charges and the distance between adjacent base pairs.

2. Triplet-Forming Thionated Donor-Acceptor Chromophores for Electrochemically Amphoteric Photosensitization

   Anna I. Wright, Benson M. Kariuki, and Yi-Lin Wu

   Eur. J. Org. Chem. 2021, 2021, 4647–4652. (DOI:10.1002/ejoc.202100793)

   • In memory of Professor François Diederich; this article also appears in François Diederich Tribute

   Abs Link

   A series of piperidine-naphthalene monoimide, donor-acceptor (D-A) chromophores and their thionated derivatives were prepared. The physical properties of the chromophores were studied by spectroscopic and electrochemical measurements and DFT calculations. Relative to their non-thionated counterparts, the thionated D-A chromophores display enhanced visible-light absorption and O-1(2)-sensitization quantum yields and negligible fluorescence, suggesting facile triplet formation of this class of molecules. This behavior originates from the significant n-pi* character in the singlet excited state, resulting in large spin-orbit coupling between the singlet/triplet manifolds regardless of the degree of D/A interactions. With the electrochemically active D/A moieties and high triplet energy, the thionated chromophores can be used as amphoteric photosensitizers to catalyze reductive and oxidative photoreactions with efficiency comparable to Ru(bpy)(3)(2+) as the sensitizer. Our results demonstrate that thiocarbonylation can be utilized in amide/imide-containing D-A chromophores to provide a wide range of heavy-atom-free redox-active photosensitizers.

2020

1. Organic room-temperature phosphorescence from halogen-bonded organic frameworks: hidden electronic effects in rigidified chromophores

   Jiawang Zhou, Ljiljana Stojanović, Andrey A. Berezin, Tommaso Battisti, Abigail Gill, Benson M. Kariuki, Davide Bonifazi, Rachel Crespo-Otero, Michael R. Wasielewski, and Yi-Lin Wu

   Chem. Sci. 2020, 12, 767–773. (DOI:10.1039/d0sc04646a)

   Abs Link

   Development of purely organic materials displaying room-temperature phosphorescence (RTP) will expand the toolbox of inorganic phosphors for imaging, sensing or display applications. While molecular solids were found to suppress non-radiative energy dissipation and make the RTP process kinetically favourable, such an effect should be enhanced by the presence of multivalent directional non-covalent interactions. Here we report phosphorescence of a series of fast triplet-forming tetraethyl naphthalene-1,4,5,8-tetracarboxylates. Various numbers of bromo substituents were introduced to modulate intermolecular halogen-bonding interactions. Bright RTP with quantum yields up to 20% was observed when the molecule is surrounded by a Brcdots, three dots, centeredO halogen-bonded network. Spectroscopic and computational analyses revealed that judicious heavy-atom positioning suppresses non-radiative relaxation and enhances intersystem crossing at the same time. The latter effect was found to be facilitated by the orbital angular momentum change, in addition to the conventional heavy-atom effect. Our results suggest the potential of multivalent non-covalent interactions for excited-state conformation and electronic control.

2. Functional Systems Derived from Nucleobase Self-assembly

   Anselmo Prado, David González-Rodríguez, and Yi-Lin Wu

   ChemistryOpen 2020, 9, 409–430. (DOI:10.1002/open.201900363)

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   Dynamic and reversible non-covalent interactions endow synthetic systems and materials with smart adaptive functions that allow them to response to diverse stimuli, interact with external agents, or repair structural defects. Inspired by the outstanding performance and selectivity of DNA in living systems, scientists are increasingly employing Watson-Crick nucleobase pairing to control the structure and properties of self-assembled materials. Two sets of complementary purine-pyrimidine pairs (guanine:cytosine and adenine:thymine(uracil)) are available that provide selective and directional H-bonding interactions, present multiple metal-coordination sites, and exhibit rich redox chemistry. In this review, we highlight several recent examples that profit from these features and employ nucleobase interactions in functional systems and materials, covering the fields of energy/electron transfer, charge transport, adaptive nanoparticles, porous materials, macromolecule self-assembly, or polymeric materials with adhesive or self-healing ability.

3. π-Extended Donor–Acceptor Porphyrins and Metalloporphyrins for Antimicrobial Photodynamic Inactivation

   Anzhela Galstyan, Yogesh Kumar Maurya, Halina Zhylitskaya, Youn Jue Bae, Yi-Lin Wu, Michael R. Wasielewski, Tadeusz Lis, Ulrich Dobrindt, and Marcin Stępień

   Chem. Eur. J. 2020, 26, 8262–8266. (DOI:10.1002/chem.201905372)

   Abs Link

   Free base, zinc and palladium pi-extended porphyrins containing fused naphthalenediamide units were employed as photosensitizers in antimicrobial photodynamic therapy (aPDT). Their efficacy, assessed by photophysical and in vitro photobiological studies on Gram-positive bacteria, was found to depend on metal coordination, showing a dramatic enhancement of photosensitizing activity for the palladium complex.

2019

1. Quantum Coherence Enhances Electron Transfer Rates to Two Equivalent Electron Acceptors

   Brian T. Phelan, Jinyuan Zhang, Guan-Jhih Huang, Yi-Lin Wu, Mehdi Zarea, Ryan M. Young, and Michael R. Wasielewski

   J. Am. Chem. Soc. 2019, 141, 12236–12239. (DOI:10.1021/jacs.9b06166)

   Abs Link

   When a molecular electron donor interacts with multiple electron acceptors, quantum coherence can enhance the electron transfer (ET) rate. Here we report photodriven ET rates in a pair of donor-acceptor (D-A) compounds that link one anthracene (An) donor to one or two equivalent 1,4-benzoquinone (BQ) acceptors. Subpicosecond ET from the lowest excited singlet state of An to two BQs is about 2.4 times faster than ET to one BQ at room temperature, but about 5 times faster at cryogenic temperatures. This factor of 2 increase results from a transition from ET to one of two acceptors at room temperature to ET to a superposition state of the two acceptors with correlated system-bath fluctuations at low temperature.

2. Design principles for efficient singlet fission in anthracene-based organic semiconductors

   Youn Jue Bae, Joseph A. Christensen, Gyeongwon Kang, Christos D. Malliakas, Jiawang Zhou, Jordan N. Nelson, Ryan M. Young, Yi-Lin Wu, Richard P. Van Duyne, George C. Schatz, and Michael R. Wasielewski

   Proc. SPIE 11084, Physical Chemistry of Semiconductor Materials and Interfaces XVIII 2019. (DOI:10.1117/12.2527346)

   Abs Link

   Singlet fission (SF) in two or more electronically coupled organic chromophores converts a high-energy singlet exciton into two low-energy triplet excitons, which can be used to increase solar cell efficiency. Many known SF chromophores are unsuitable for device applications due to chemical instability and low triplet state energies. This work summarizes structurally dependent SF dynamics for 9,10-bis(phenylethynyl)anthracene (BPEA) and its derivatives in the solid-state using time-resolved optical spectroscopies, and electronic structure calculations. By modulating the packing structure in thin films, we can effectively tune electronic energy and coupling. The systematic study in BPEA organic semiconductors shows that maximizing the thermodynamic driving force can achieve the highest SF rate and efficiency.

3. Competition between Singlet Fission and Spin‐Orbit‐Induced Intersystem Crossing in Anthanthrene and Anthanthrone Derivatives

   Youn Jue Bae, Matthew D. Krzyaniak, Marek B. Majewski, Maude Desroches, Jean-François Morin, Yi-Lin Wu, and Michael R. Wasielewski

   ChemPlusChem 2019, 84, 1432–1438. (DOI:10.1002/cplu.201900410)

   Abs Link

   Singlet and triplet excited-state dynamics of anthanthrene and anthanthrone derivatives in solution are studied. Triisopropylsilyl- (TIPS) or H-terminated ethynyl groups are used to tune the singlet and triplet energies to enable their potential applications in singlet fission and triplet fusion processes. Time-resolved optical and electron paramagnetic resonance (EPR) spectroscopies are used to obtain a mechanistic understanding of triplet formation. The anthanthrene derivatives form triplet states efficiently at a rate (ca. 107 s−1) comparable to radiative singlet fluorescence processes with approximately 30 % triplet yields, despite their large S1-T1 energy gap (>1 eV) and the lack of carbonyl groups. In contrast, anthanthrone has a higher triplet yield (50±10 %) with a faster intersystem crossing rate (2.7urn:x-wiley:21926506:media:cplu201900410:cplu201900410-math-0001 108 s−1) because of the n-π* character of the S1←S0 transition. Analysis of time-resolved spin-polarized EPR spectra of these compounds reveals that the triplet states are primarily generated by the spin-orbit-induced intersystem crossing mechanism. However, at high concentrations, the EPR spectrum of the 4,6,10,14-tetrakis(TIPS-ethynyl)anthanthrene triplet state shows a significant contribution from a non-Boltzmann population of the ms=0 spin sublevel, which is characteristic of triplet formation by singlet fission.

4. Substituent effects on energetics and crystal morphology modulate singlet fission in 9,10-bis(phenylethynyl)anthracenes

   Youn Jue Bae, Joseph A. Christensen, Gyeongwon Kang, Jiawang Zhou, Ryan M. Young, Yi-Lin Wu, Richard P. Van Duyne, George C. Schatz, and Michael R. Wasielewski

   J. Chem. Phys. 2019, 151, 044501. (DOI:10.1063/1.5110411)

   Abs Link

   Singlet fission (SF) converts a singlet exciton into two triplet excitons in two or more electronically coupled organic chromophores, which may then be used to increase solar cell efficiency. Many known SF chromophores are unsuitable for device applications due to chemical instability or low triplet state energies. The results described here show that efficient SF occurs in derivatives of 9,10-bis(phenylethynyl)anthracene (BPEA), which is a highly robust and tunable chromophore. Fluoro and methoxy substituents at the 4- and 4’-positions of the BPEA phenyl groups control the intermolecular packing in the crystal structure, which alters the interchromophore electronic coupling, while also changing the SF energetics. The lowest excited singlet state (S1) energy of 4,4’-difluoro-BPEA is higher than that of BPEA so that the increased thermodynamic favorability of SF results in a (16 +/- 2 ps)(-1) SF rate and a 180% +/- 16% triplet yield, which is about an order of magnitude faster than BPEA with a comparable triplet yield. By contrast, 4-fluoro-4’-methoxy-BPEA and 4,4’-dimethoxy-BPEA have slower SF rates, (90 +/- 20 ps)(-1) and (120 +/- 10 ps)(-1), and lower triplet yields, (110 +/- 4)% and (168 +/- 7)%, respectively, than 4,4’-difluoro-BPEA. These differences are attributed to changes in the crystal structure controlling interchromophore electronic coupling as well as SF energetics in these polycrystalline solids.

5. Transient Two-Dimensional Electronic Spectroscopy: Coherent Dynamics at Arbitrary Times along the Reaction Coordinate

   Aritra Mandal, Jonathan D. Schultz, Yi-Lin Wu, Adam F. Coleman, Ryan M. Young, and Michael R. Wasielewski

   J. Phys. Chem. Lett. 2019, 10, 3509–3515. (DOI:10.1021/acs.jpclett.9b00826)

   Abs Link

   Recent advances in two-dimensional electronic spectroscopy (2DES) have enabled identification of fragile quantum coherences in condensed-phase systems near the equilibrium molecular geometry. In general, traditional 2DES cannot measure such coherences associated with photophysical processes that occur at times significantly after the initially prepared state has dephased, such as the evolution of the initial excited state into a charge transfer state. We demonstrate the use of transient two-dimensional electronic spectroscopy (t-2DES) to probe coherences in an electron donor-acceptor dyad consisting of a perylenediimide (PDI) acceptor and a perylene (Per) donor. An actinic pump pulse prepares the lowest excited singlet state of PDI followed by formation of the PDI(*-)-Per(*+) ion pair, which is probed at different times following the actinic pulse using 2DES. Analysis of the observed coherences provides information about electronic, vibronic, and vibrational interactions at any time along the reaction coordinate for ion pair formation.

2018

1. Photoexcited Naphthalene Diimide Radical Anion Linking the Nodes of a Metal-Organic Framework: A Heterogeneous Super-reductant

   Subhadip Goswami, Jordan N. Nelson, Timur Islamoglu, Yi-Lin Wu, Omar K. Farha, and Michael R. Wasielewski

   Chem. Mater. 2018, 30, 2488–2492. (DOI:10.1021/acs.chemmater.8b00720)

   Abs Link

   Photoredox chem. empowers reactions with high chem. potentials, and remarkably strong super-reductants can be achieved by photoexciting solar-absorbing radical anion chromophores. By incorporating anions of naphthalene diimide (NDI.bul.-) into a Zr-based metal-org. framework (MOF), we demonstrate in this work that the NDI.bul.- super-reductant can be arranged into the porous and cryst. MOF scaffold, which preserves its monomer-like photochem. without undesired intermol. deactivation. The strong reducing power of this MOF was showcased by the redn. of aliph. chlorinated hydrocarbons, and the formation of carbon-centered radical products as evidenced by EPR spin-trapping expts. [on SciFinder(R)]

2. Fully Conjugated [4]Chrysaorene. Redox-Coupled Anion Binding in a Tetraradicaloid Macrocycle

   Hanna Gregolinska, Marcin Majewski, Piotr J. Chmielewski, Janusz Gregolinski, Alan Chien, Jiawang Zhou, Yi-Lin Wu, Youn Jue Bae, Michael R. Wasielewski, Paul M. Zimmerman, and Marcin Stępień

   J. Am. Chem. Soc. 2018, 140, 14474–14480. (DOI:10.1021/jacs.8b09385)

   Abs Link

   [4]Chrysaorene, a fully conjugated carbocyclic coronoid, is shown to be a low-bandgap π-conjugated system with a distinct open-shell character. The system shows good chem. stability and can be oxidized to well-defined radical cation and dication states. The cavity of [4]chrysaorene acts as an anion receptor toward halide ions with a particular selectivity toward iodides (Ka = 207 ± 6 M-1). The interplay between anion binding and redox chem. is demonstrated using a 1H NMR anal. in soln. In particular, a well-resolved, paramagnetically shifted spectrum of the [4]chrysaorene radical cation is obsd., providing evidence for the inner binding of the iodide. The radical cation-iodide adduct can be generated in thin solid films of [4]chrysaorene by simple exposure to diiodine vapor. [on SciFinder(R)]

3. Fluorescent excimers and exciplexes of the purine base derivative 8-phenylethynyl-guanine in DNA hairpins

   Kristen E. Brown, Arunoday P. N. Singh, Yi-Lin Wu, Lin Ma, Ashutosh K. Mishra, Brian T. Phelan, Ryan M. Young, Frederick D. Lewis, and Michael R. Wasielewski

   Faraday Discuss. 2018, 207, 217–232. (DOI:10.1039/C7FD00186J)

   Abs Link

   The ground- and excited-state electronic interactions between the nucleobase analog 8-(4’-phenylethynyl)deoxyguanosine, with natural nucleobases and 7-deazaguanine, as well as between adjacent EG base analogs, have been characterized using a combination of steady-state spectroscopy and time-resolved fluorescence, absorption, and stimulated Raman spectroscopies. The properties of the nucleoside EG-H2 are only weakly perturbed upon incorporation into synthetic DNA hairpins in which thymine, cytosine or adenine are the bases flanking EG. Incorporation of the nucleoside to be adjacent to guanine or deazaguanine results in the formation of short-lived (40-80 ps) exciplexes, the charge transfer character of which increases as the oxidn. potential of the donor decreases. Hairpins possessing two or three adjacent EG base analogs display exciton-coupled CD in the ground state and form long-lived fluorescent excited states upon electronic excitation. Incorporation of EG into the helical scaffold of the DNA hairpins places it adjacent to its neighboring nucleobases or a second EG, thus providing the close proximity required for the formation of exciplex or excimer intermediates upon geometric relaxation of the short-lived EG excited state. The three time-resolved spectroscopic methods employed permit both the characterization of the several intermediates and the kinetics of their formation and decay. [on SciFinder(R)]

4. Singlet Fission in 9,10-Bis(phenylethynyl)anthracene Thin Films

   Youn Jue Bae, Gyeongwon Kang, Christos D. Malliakas, Jordan N. Nelson, Jiawang Zhou, Ryan M. Young, Yi-Lin Wu, Richard P. Van Duyne, George C. Schatz, and Michael R. Wasielewski

   J. Am. Chem. Soc. 2018, 140, 15140–15144. (DOI:10.1021/jacs.8b07498)

   Abs Link

   Singlet fission (SF) in two or more electronically coupled org. chromophores converts a high-energy singlet exciton into two low-energy triplet excitons, which can be used to increase solar cell efficiency. Many known SF chromophores are unsuitable for device applications due to chem. instability and low triplet state energies. The results described here show that efficient SF occurs in polycryst. thin films of 9,10-bis(phenylethynyl)anthracene (BPEA), a com. dye that has singlet and triplet energies of 2.40 and 1.11 eV, resp., in the solid state. BPEA crystallizes into two polymorphs with space groups C2/c and Pbcn, which undergo SF with ksfa = (109 ± 4 ps)-1 and ksfb = (490 ± 10 ps)-1, resp. The high triplet energy and efficient SF evidenced from the 180 ± 20% triplet yield make BPEA a promising candidate for enhancing solar cell performance. [on SciFinder(R)]

5. Charge-Transfer Character in a Covalent Diketopyrrolopyrrole Dimer: Implications for Singlet Fission

   Catherine M. Mauck, Youn Jue Bae, Michelle Chen, Natalia Powers-Riggs, Yi-Lin Wu, and Michael R. Wasielewski

   ChemPhotoChem 2018, 2, 223–233. (DOI:10.1002/cptc.201700135)

   Abs Link

   Diketopyrrolopyrrole (DPP) is a strongly absorbing, photostable chromophore that can undergo singlet fission (SF), a photophys. process that promises to significantly enhance solar-cell performance. In the solid state, DPP packs in a herringbone arrangement that maximizes intermol. donor-acceptor interactions, suggesting that charge-transfer (CT) states play a role in DPP SF. In order to characterize intermol. DPP CT states in mol. assemblies, we have synthesized a covalent DPP dimer bridged by a xanthene linker, which places two thiophene-substituted DPPs (TDPPs) in a cofacial arrangement that mimics chromophore π-π stacking in the thin film. After photoexcitation in polar solvents, symmetry-breaking charge sepn. forms the fully charge sepd. TDPP+.-TDPP-. ion-pair state. In nonpolar solvents, charge sepn. is incomplete leading to the TDPPδ+-TDPPδ- CT state, which is in pseudoequil. with the relaxed S1S0 state obsd. by transient absorption and emission spectroscopy. This study highlights the importance of intramol. coupling as well as the importance of entropy to promoting SF in chromophore dimers for which SF is endo- or isoergic. [on SciFinder(R)]

6. Tunable Crystallinity and Charge Transfer in Two-Dimensional G-Quadruplex Organic Frameworks

   Yi-Lin Wu, N. Scott Bobbitt, Jenna L. Logsdon, Natalia E. Powers-Riggs, Jordan N. Nelson, Xiaolong Liu, Timothy C. Wang, Randall Q. Snurr, Joseph T. Hupp, Omar K. Farha, Mark C. Hersam, and Michael R. Wasielewski

   Angew. Chem. Int. Ed. 2018, 57, 3985–3989. (DOI:10.1002/anie.201800230)

   Abs Link

   DNA G-quadruplex structures were recently discovered to provide reliable scaffolding for two-dimensional organic frameworks due to the strong hydrogen-bonding ability of guanine. Herein, 2,7-diaryl pyrene building blocks with high HOMO energies and large optical gaps are incorporated into G-quadruplex organic frameworks. The adjustable substitution on the aryl groups provides an opportunity to elucidate the framework formation mechanism; molecular non-planarity is found to be beneficial for restricting interlayer slippage, and the framework crystallinity is highest when intermolecular interaction and non-planarity strike a fine balance. When guanine-functionalized pyrenes are co-crystallized with naphthalene diimide, charge-transfer (CT) complexes are obtained. The photophysical properties of the pyrene-only and CT frameworks are characterized by UV/Vis and steady-state and time-resolved photoluminescence spectroscopies, and by EPR spectroscopy for the CT complex frameworks.

2017

1. G-quadruplex organic frameworks

   Yi-Lin Wu, Noah E. Horwitz, Kan-Sheng Chen, Diego A. Gomez-Gualdron, Norman S. Luu, Lin Ma, Timothy C. Wang, Mark C. Hersam, Joseph T. Hupp, Omar K. Farha, Randall Q. Snurr, and Michael R. Wasielewski

   Nat. Chem. 2017, 9, 466–472. (DOI:10.1038/nchem.2689)

   Abs Link

   Two-dimensional covalent organic frameworks often pi stack into crystalline solids that allow precise spatial positioning of molecular building blocks. Inspired by the hydrogen-bonded G-quadruplexes found frequently in guanine-rich DNA, here we show that this structural motif can be exploited to guide the self-assembly of naphthalene diimide and perylene diimide electron acceptors end-capped with two guanine electron donors into crystalline G-quadruplex-based organic frameworks, wherein the electron donors and acceptors form ordered, segregated pi-stacked arrays. Time-resolved optical and electron paramagnetic resonance spectroscopies show that photogenerated holes and electrons in the frameworks have long lifetimes and display recombination kinetics typical of dissociated charge carriers. Moreover, the reduced acceptors form polarons in which the electron is shared over several molecules. The G-quadruplex frameworks also demonstrate potential as cathode materials in Li-ion batteries because of the favourable electron-and Li-ion-transporting capacity provided by the ordered rylene diimide arrays and G-quadruplex structures, respectively.

2. Electron Hopping and Charge Separation within a Naphthalene-1,4:5,8-bis(dicarboximide) Chiral Covalent Organic Cage

   Tomáš Šolomek, Natalia E. Powers-Riggs, Yi-Lin Wu, Ryan M. Young, Matthew D. Krzyaniak, Noah E. Horwitz, and Michael R. Wasielewski

   J. Am. Chem. Soc. 2017, 139, 3348–3351. (DOI:10.1021/jacs.7b00233)

   Abs Link

   We present the stereoselective synthesis of a chiral covalent organic cage consisting of three redox-active naphthalene-1,4:5,8-bis(dicarboximide) (NDI) units by dynamic imine chemistry. Single crystal X-ray diffraction analysis shows that host guest interactions and racemic cocrystallization allow for controlling the solid state structure. Electronic interactions between the NDI units probed by absorption and circular dichroism spectroscopies, electrochemistry and theoretical calculations are shown to be weak. Photoexcitation of NDI leads to intracage charge separation with a longer lifetime than observed in the corresponding monomeric NDI and dimeric NDI cyclophane imines. The EPR spectrum of the singly reduced cage shows that the electron is localized on a single NDI unit at ambient temperatures and transitions to rapid hopping among all three NDI units upon heating to 350 K. Dynamic covalent chemistry thus promises rapid access to covalent organic cages with well-defined architectures to study charge accumulation and electron transport phenomena.

3. Atomistic Approach toward Selective Photocatalytic Oxidation of a Mustard-Gas Simulant: A Case Study with Heavy-Chalcogen-Containing PCN-57 Analogues

   Subhadip Goswami, Claire E. Miller, Jenna L. Logsdon, Cassandra T. Buru, Yi-Lin Wu, David N. Bowman, Timur Islamoglu, Abdullah M. Asiri, Christopher J. Cramer, Michael R. Wasielewski, Joseph T. Hupp, and Omar K. Farha

   ACS Appl. Mater. Interfaces 2017, 9, 19535–19540. (DOI:10.1021/acsami.7b07055)

   Abs Link

   Here we describe the synthesis of two Zr-based benzothiadiazole- and benzoselenadiazole-containing metalorganic frameworks (MOFs) for the selective photocatalytic oxidation of the mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES). The photophysical properties of the linkers and MOFs are characterized by steady-state absorption and emission, time-resolved emission, and ultrafast transient absorption spectroscopy. The benzoselenadiazole-containing MOF shows superior catalytic activity compared to that containing benzothiadiazole with a half-life of 3.5 min for CEES oxidation to nontoxic 2-chloroethyl ethyl sulfoxide (CEESO). Transient absorption spectroscopy performed on the benzoselenadiazole linker reveals the presence of a triplet excited state, which decays with a lifetime of 9.4 mu s, resulting in the generation of singlet oxygen for photocatalysis. This study demonstrates the effect of heavy chalcogen substitution within a porous framework for the modulation of photocatalytic activity.

4. Tracking Hole Transport in DNA Hairpins Using a Phenylethynylguanine Nucleobase

   Kristen E. Brown, Arunoday P. N. Singh, Yi-Lin Wu, Ashutosh Kumar Mishra, Jiawang Zhou, Frederick D. Lewis, Ryan M. Young, and Michael R. Wasielewski

   J. Am. Chem. Soc. 2017, 139, 12084–12092. (DOI:10.1021/jacs.7b06998)

   Abs Link

   The hole transport dynamics of DNA hairpins possessing a stilbene electron acceptor and donor along with a modified guanine (G) nucleobase, specifically 8-(4’-phenylethynyl)deoxyguanosine (EG) were investigated. The nearly indistinguishable oxidn. potentials of EG and G and unique spectroscopic characteristics of EG+.bul. make it well-suited for directly observing transient hole occupation during charge transport between a stilbene electron donor and acceptor. In contrast to the cation radical G+.bul., EG+.bul. possesses a strong absorption near 460 nm and has a distinct Raman-active ethynyl stretch. Both spectroscopic characteristics are easily distinguished from those of the stilbene donor/acceptor radical ion chromophores. Here, employing EG, we obsd. its role as a shallow hole trap, or as an intermediate hole transport site when a deeper trap state was present. Using a combination of ultrafast absorption and stimulated Raman spectroscopies, the hole-transport dynamics were obsd. to be similar in systems having EG vs. G bases, with small perturbations to the charge transport rates and yields. These results showed that EG can be deployed at specified locations throughout the sequence to report on hole occupancy, thereby enabling detailed monitoring of the hole transport dynamics with base-site specificity. [on SciFinder(R)]

5. Photoinduced charge recombination in dipolar D-A-A photonic liquid crystal polymorphs

   Mercedes M. A. Mazza, Shiori Yamazaki, Dieu X. Mai, Suyog Padgaonkar, Samuel Peurifoy, Ariane Goncalves, Yi-Lin Wu, Qiaoyu Hu, and Amy M. Scott

   Phys. Chem. Chem. Phys. 2017, 19, 4588–4596. (DOI:10.1039/C6CP08631D)

   Abs Link

   A hexylalkoxy dipolar D-A-A mol. [7-(4-N,N-(bis(4-hexyloxyphenyl)amino)phenyl)-2,1,3-(benzothia-diazol-4-yl)methylene]propane-dinitrile, (C6-TPA-BT-CN) has been synthesized and the photophysics studied via femtosecond transient absorption spectroscopy (FsTA) in toluene and in amorphous and liq. cryst. spherulite thin films. Two spherulite macromol. cryst. phases (banded and non-banded) were obsd. through concn. dependent, soln. processing techniques and were birefringent with a neg. sign of elongation. A dramatic change in the electronic absorption from blue in amorphous films to green in spherulites was obsd., and the mol. orientation was detd. through the combined anal. of polarized light microscopy, x-ray diffraction, and SEM. FsTA was performed on amorphous films and showed complex charge recombination dynamics, and a Stark effect, characterized from the combined TPA+ ̇and [BT-CN]- ̇spectroscopic signatures at 450 nm and 510 nm and identified through spectroelectrochem. Radical cation dynamics of TPA+ ̇were obsd. selectively at 750 nm with \textgreater503.3 ps (18%) recombination kinetics resulting in a rather significant yield of free charge carriers in amorphous films and consistent with previous reports on energetically disordered blend films. However, photoexcitation on large, non-banded spherulites areas (\textgreater250 μm) reveal av. monoexponential charge recombination lifetimes of 169.2 ps from delocalized states similar to those obsd. in amorphous films and are 5× longer-lived than previous reports [Chang et al., J. Am. Chem. Soc., 2013, 135, 8790] of a related methyl-DPAT-BT-CN whose amorphous thin films were prepd. through vapor deposition. Thus, the correlation between the microstructure of the blend film and the photoinduced radical pair dynamics described here is crit. for developing a fundamental understanding of how dipolar states contribute to the charge carrier yield in a disordered energy system. [on SciFinder(R)]

6. Influence of Anion Delocalization on Electron Transfer in a Covalent Porphyrin Donor-Perylenediimide Dimer Acceptor System

   Patrick E. Hartnett, Catherine M. Mauck, Michelle A. Harris, Ryan M. Young, Yi-Lin Wu, Tobin J. Marks, and Michael R. Wasielewski

   J. Am. Chem. Soc. 2017, 139, 749–756. (DOI:10.1021/jacs.6b10140)

   Abs Link

   The effects of anion delocalization on electron transfer has been studied using zinc meso-tetraphenylporphyrin (ZnTPP) as a donor and a perylene-3,4:9,10-bis(dicarboximide) dimer as the acceptor (PDI2). The PDI units of the dimer are positioned in a cofacial orientation relative to one another by attachment of the imide group of each PDI to the 4- and 5-positions of a xanthene spacer. The distal imide group of one PDI is linked to the para-position of one ZnTPP Ph group to yield ZnTPP-PDI2. The data for the dimer are compared to two different ZnTPP-PDI monomer ref. systems designed to probe electron transfer to each of the individual PDI mols. comprising PDI2. The electron transfer rate from the ZnTPP lowest excited singlet state to PDI2 is increased by 50% relative to that in ZnTPP-PDI, when the data are cor. for the statistics of having two electron acceptors. Femtosecond transient IR absorption spectroscopy provides evidence that the obsd. enhancement in charge sepn. results from electron transfer producing a delocalized PDI2 anion. [on SciFinder(R)]

7. Substituent Effects on Singlet Exciton Fission in Polycrystalline Thin Films of Cyano-Substituted Diaryltetracenes

   Eric A. Margulies, Nicolas Kerisit, Przemyslaw Gawel, Catherine M. Mauck, Lin Ma, Claire E. Miller, Ryan M. Young, Nils Trapp, Yi-Lin Wu, Francois Diederich, and Michael R. Wasielewski

   J. Phys. Chem. C 2017, 121, 21262–21271. (DOI:10.1021/acs.jpcc.7b07870)

   Abs Link

   Cyano-substituted tetracenes (5,11-dicyano-6,12-diphenyltetracene, Tet) undergo exoergic singlet fission (SF), a spin-allowed photophys. process that generates a pair of triplet excitons from one singlet exciton. To elucidate substituent effects on SF, we have measured the SF dynamics and triplet yields of thin films, formed by Tet bearing hydrogen (H), Me (Me), fluoro (F), and trimethylsilyl (TMS) substituents on the p-Ph positions and on the 3 and 9 positions of the tetracene core, by time-resolved spectroscopy in the vis-NIR and IR regions. The H-, Me-, and F-Tet display strong intramol. electronic coupling (π-π distances \textless4 Å), and SF gives high triplet exciton yields up to 200% (quant.). In addn., a charge-transfer state mediates SF in F-Tet films, while H-Tet and Me-Tet show no evidence for such a state. Correlations between the SF yields and the crystal structure show that chromophore slippage along both their short and long axes allows efficient SF and that a large degree of π contact between the chromophores is not necessary for rapid and efficient SF in the solid state. As expected, the large interchromophore distance in TMS-Tet (\textgreater4 Å) reduces its SF triplet yield to about 60%. [on SciFinder(R)]

8. Singlet fission within diketopyrrolopyrrole nanoparticles in water

   Catherine M. Mauck, Patrick E. Hartnett, Yi-Lin Wu, Claire E. Miller, Tobin J. Marks, and Michael R. Wasielewski

   Chem. Mater. 2017, 29, 6810–6817. (DOI:10.1021/acs.chemmater.7b01845)

   Abs Link

   Nanoparticles (NPs) of the singlet fission chromophore 3,6-bis(5-phenylthiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (PhTDPP) having av. hydrodynamic diams. of 63-193 nm were prepd. by rapidly injecting variable concns. of PhTDPP solns. in THF into water. These PhTDPP NPs are stable over months in water and exhibit fluorescence quantum yields «1%. Femtosecond transient absorption spectroscopy shows that singlet fission is more rapid in smaller NPs, likely reflecting their greater surface area-to-vol. ratio and consequent exposure of more mols. to the high dielec. aq. environment. These observations suggest that charge transfer states, whose energy is sensitive to the dielec. const. of the surrounding medium, serve as virtual intermediates in PhTDPP NP singlet fission. However, the lifetime of the triplet excitons produced by singlet fission is longest in the larger NPs having greater long-range order, which allows the triplet excitons to diffuse further from one another thus slowing triplet-triplet annihilation. [on SciFinder(R)]

2016

1. Photoinduced charge and energy transfer within meta- and para-linked chlorophyll a-perylene-3,4:9,10-bis(dicarboximide) donor-acceptor dyads

   Guan-Jhih Huang, Michelle A. Harris, Matthew D. Krzyaniak, Eric A. Margulies, Scott M. Dyar, Rebecca J. Lindquist, Yilei Wu, Vladimir V. Roznyatovskiy, Yi-Lin Wu, Ryan M. Young, and Michael R. Wasielewski

   J. Phys. Chem. B 2016, 120, 756–765. (DOI:10.1021/acs.jpcb.5b10806)

   Abs Link

   Connecting electron donors and acceptors to a benzene ring in a meta or para relationship results in quantum interference effects that can strongly influence charge separation (CS) and charge recombination (CR) processes in these systems. We report on the energy and electron transfer behavior of chlorophyll-based para- and meta-linked donor-bridge acceptor (D-B-A) dyads, where the semisynthetic chlorophyll a derivative, zinc methyl 3-ethyl-pyrochlorophyllide a (D), is covalently attached at its 20-position to the para position of one phenyl of diphenylacetylene (B). The meta or para position of the phenyl in B distal to the donor is in turn attached to perylene-3,4:9,10-bis(dicarboximide) (PDI) (A). Photoexcitation of the D-B-A dyads produces long-lived radical ion pairs D center dot+-B-A(center dot-), which recombine to the ground state and to both (3)*D-B-A and D-B-(3)*A. Time-resolved optical and electron paramagnetic resonance spectroscopies were used to monitor the charge transfer and triplet energy transfer (TEnT) processes. At longer times, TEnT occurs from 3*D-B-A to D-B-(3)*A. Surprisingly, the D-B-A molecules linked via the meta linkage exhibit faster CS, CR, and TEnT rates than do those with the para linkage in contrast to most other meta/para-linked D-B-A molecules previously examined.

2. Effects of Crystal Morphology on Singlet Exciton Fission in Diketopyrrolopyrrole Thin Films

   Patrick E. Hartnett, Eric A. Margulies, Catherine M. Mauck, Stephen A. Miller, Yilei Wu, Yi-Lin Wu, Tobin J. Marks, and Michael R. Wasielewski

   J. Phys. Chem. B 2016, 120, 1357–1366. (DOI:10.1021/acs.jpcb.5b10565)

   Abs Link

   Singlet exciton fission (SF) is a promising strategy for increasing photovoltaic efficiency, but in order for SF to be useful in solar cells, it should take place in a chromophore that is air-stable, highly absorptive, soln. processable, and inexpensive. Unlike many SF chromophores, diketopyrrolopyrrole (DPP) conforms to these criteria, and here we investigate SF in DPP for the first time. SF yields in thin films of DPP derivs., which are widely used in org. electronics and photovoltaics, are shown to depend critically on crystal morphol. Time-resolved spectroscopy of three DPP derivs. with Ph (3,6-diphenylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, PhDPP), thienyl (3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, TDPP), and phenylthienyl (3,6-di(5-phenylthiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, PhTDPP) arom. substituents in 100-200 nm thin films reveals that efficient SF occurs only in TDPP and PhTDPP (τSF = 220 ± 20 ps), despite the fact that SF is most exoergic in PhDPP. This result correlates well with the greater degree of π-overlap and closer π-stacking in TDPP (3.50 Å) and PhTDPP (3.59 Å) relative to PhDPP (3.90 Å) and demonstrates that SF in DPP is highly sensitive to the electronic coupling between adjacent chromophores. The triplet yield in PhTDPP films is detd. to be 210 ± 35% by the singlet depletion method and 165 ± 30% by the energy transfer method, showing that SF is nearly quant. in these films and that DPP derivs. are a promising class of SF chromophores for enhancing photovoltaic performance. [on SciFinder(R)]

2015

1. Photoinduced Hole Injection into a Self-Assembled pi-Extended G-Quadruplex

   Yi-Lin Wu, Kristen E. Brown, Daniel M. Gardner, Scott M. Dyar, and Michael R. Wasielewski

   J. Am. Chem. Soc. 2015, 137, 3981–3990. (DOI:10.1021/jacs.5b00977)

   • Highlighted in JACS Spotlights. J. Am. Chem. Soc. 2015, 137, 3995. (DOI: 10.1021/jacs.5b02864)

   Abs Link

   We have prepared a G-quadruplex (GQ:1) that incorporates an 8-(4’-aminophenylethynyl)guanine (GEAn) electron donor covalently attached to a 4-aminonaphthalene-1,8-imide (ANT) chromophore and a naphthalene-1,8:4,5-bis-(dicarboximide) (NDI) electron acceptor (GEAn-ANI-NDI, 1). In the presence of KPF6 in tetrahydrofuran (THE), 1 self-assembles into a monodisperse, C-4-symmetric GQ:1 with small spatial intraquadruplex overlap between the ANI-NDI units. Photoexcitation of monomeric 1 induces the two-step charge transfer GEAn-1*ANI-NDI -\textgreater GEAn(+center dot)-ANI(-center dot)-NDI -\textgreater GEAn(+center dot)-ANI-NDI-center dot that occurs in tau(CSI) = 5 ps and tau(CS2) = 330 ps, respectively, while charge recombination in ca. 300 ns. Sharpening of the GEAn(+center dot) transient absorption and a shift of the ethynyl vibrational frequency in 1 were observed, concomitant with the stepwise electron transfer from ANI(-center dot) to NDI. Formation of GQ:1 from 1 in THE increases the secondary charge-shifting rate (tau(CS2) = 110 ps) and results in no change in ethynyl vibrational frequency. Charge recombination in GQ:1 is slowed by enhanced radical-pair intersystem crossing driven by the greater number of hyperfine couplings in the assembly. Moreover, time-resolved EPR spectroscopy shows that the spin spin-exchange interaction (J) between the radicals of GEAn(+center dot)-ANI-NDI-center dot within GQ-1 is smaller than that of 1, suggesting that the spin (charge) density in GEAn(+center dot) is more dispersed in GQ-1. The spectroscopic results are consistent with hole sharing among the guanines within the G-quadruplex that is kinetically competitive with the formation of GEAn(+center dot). This suggests that G-quadruplexes can serve as effective hole conduits in ordered donor-acceptor assemblies.

2. Sub-Picosecond Singlet Exciton Fission in Cyano-Substituted Diaryltetracenes

   Eric A. Margulies, Yi-Lin Wu, Przemyslaw Gawel, Stephen A. Miller, Leah E. Shoer, Richard D. Schaller, Francois Diederich, and Michael R. Wasielewski

   Angew. Chem. Int. Ed. 2015, 54, 8679–8683. (DOI:10.1002/anie.201501355)

   Abs Link

   Thin films of 5,11-dicyano-6,12-diphenyltetracene (TcCN) have been studied for their ability to undergo singlet exciton fission (SF). Functionalization of tetracene with cyano substituents yields a more stable chromophore with favorable energetics for exoergic SF (2E(T1)-E(S1)=-0.17 eV), where S1 and T1 are singlet and triplet excitons, resp. As a result of tuning the triplet-state energy, SF is faster in TcCN relative to the corresponding endoergic process in tetracene. SF proceeds with two time consts. in the film samples (τ=0.8±0.2 ps and τ=23±3 ps), which is attributed to structural disorder within the film giving rise to one population with a favorable interchromophore geometry, which undergoes rapid SF, and a second population in which the initially formed singlet exciton must diffuse to a site at which this favorable geometry exists. A triplet yield anal. using transient absorption spectra indicates the formation of 1.6±0.3 triplets per initial excited state. [on SciFinder(R)]

3. Push-Pull Buta-1,2,3-trienes: Exceptionally Low Rotational Barriers of Cumulenic C=C Bonds and Proacetylenic Reactivity

   Przemyslaw Gawel, Yi-Lin Wu, Aaron D. Finke, Nils Trapp, Michal Zalibera, Corinne Boudon, Jean-Paul Gisselbrecht, W. Bernd Schweizer, Georg Gescheidt, and Francois Diederich

   Chem. Eur. J. 2015, 21, 6215–6225. (DOI:10.1002/chem.201406583)

   Abs Link

   A variety of asym. donor-acceptor-substituted [3]cumulenes (buta-1,2,3-trienes) were synthesized by developed procedures. The activation barriers to rotation ΔG≠ were measured by variable temp. NMR spectroscopy and are ≥11.8 kcal mol-1, in the range of the barriers for rotation around sterically hindered single bonds. The central C=C bond of the push-pull-substituted [3]cumulene moiety is shortened down to 1.22 Å as measured by x-ray crystallog., leading to a substantial bond length alternation (BLA) of up to 0.17 Å. All the exptl. results are supported by DFT calcns. Zwitterionic transition states (TS) of bond rotation confirm the postulated proacetylenic character of donor-acceptor [3]cumulenes. Addnl. support for the proacetylenic character of these chromophores is provided by their reaction with tetracyanoethene (TCNE) in a cycloaddn.-retroelectrocyclization (CA-RE) cascade characteristic of donor-polarized acetylenes. [on SciFinder(R)]

4. Complexation of Polyoxometalates with Cyclodextrins

   Yilei Wu, Rufei Shi, Yi-Lin Wu, James M. Holcroft, Zhichang Liu, Marco Frasconi, Michael R. Wasielewski, Hui Li, and J. Fraser Stoddart

   J. Am. Chem. Soc. 2015, 137, 4111–4118. (DOI:10.1021/ja511713c)

   Abs Link

   Although complexation of hydrophilic guests inside the cavities of hydrophobic hosts is considered to be unlikely, we demonstrate herein the complexation between gamma- and beta-cyclodextrins (gamma- and beta-CDs) with an archetypal polyoxometalate (POM)-namely, the [PMo12O40](3-) trianion-which has led to the formation of two organic-inorganic hybrid 2:1 complexes, namely [La(H2O)(9)]{[PMo12O40]subset of[gamma-CD](2)} (CD-POM-1) and [La(H2O)(9)] {[PMo12O40]subset of[beta-CD](2)} (CD-POM-2), in the solid state. The extent to which these complexes assemble in solution has been investigated by (i) H-1, C-13, and P-31 NMR spectroscopies and (ii) small- and wide-angle X-ray scattering, as well as (iii) mass spectrometry. Single-crystal X-ray diffraction reveals that both complexes have a sandwich-like structure, wherein one [PMo12O40](3-) trianion is encapsulated by the primary faces of two CD tori through intermolecular [C-H center dot center dot center dot O-Mo] interactions. X-ray crystal superstructures of CD-POM-1 and CD-POM-2 show also that both of these 2:1 complexes are lined up longitudinally in a one-dimensional columnar fashion by means of [O-H center dot center dot center dot O] interactions. A beneficial nanoconfinement-induced stabilizing effect is supported by the observation of slow color changes for these supermolecules in aqueous solution phase. Electrochemical studies show that the redox properties of [PMo12O40](3-) trianions encapsulated by CDs in the complexes are largely preserved in solution. The supramolecular complementarity between the CDs and the [PMo12O40](3-) trianion provides yet another opportunity for the functionalization of POMs under mild conditions by using host-guest chemistry.

2014

1. Self-Assembly of Supramolecular Light-Harvesting Arrays from Symmetric Perylene-3,4-dicarboximide Trefoils

   Kelly M. Lefler, Chul Hoon Kim, Yi-Lin Wu, and Michael R. Wasielewski

   J. Phys. Chem. Lett. 2014, 5, 1608–1615. (DOI:10.1021/jz500626g)

   Abs Link

   Unlike the widely studied perylene-3,4:9,10-bis(dicarboximide) (PDI) dyes, self-assembly of the corresponding perylene-3,4-dicarboximide (PMI) dyes into large arrays and studies of their excited state properties have received far less attention. Two sym. PMI trefoils were synthesized by connecting the 9-position of the perylene core either directly (1) or through a phenylene linker (2) to the 1,3,5-positions of a central benzene ring. Synchrotron-based small- and wide-angle x-ray scattering measurements in methylcyclohexane show that trefoil 1 self-assembles into cofacial trimers (13) on av., while trefoil 2 forms much larger assemblies that are tridecamers (213) on av. Their photophysics were characterized using steady-state as well as transient absorption and emission spectroscopy. Time-resolved spectroscopy reveals that both 13 and 213 initially form excitonically coupled excited states that subsequently relax to excimer states having 20 and 8.4 ns lifetimes, resp., which decay to ground-state primarily nonradiatively. The data are consistent with stronger electronic coupling between the PMI mols. in 213 relative to 13. [on SciFinder(R)]

2013

1. Extending Photoinduced Charge Separation Lifetimes by Using Supramolecular Design: Guanine-Perylenediimide G-Quadruplex

   Yi-Lin Wu, Kristen E. Brown, and Michael R. Wasielewski

   J. Am. Chem. Soc. 2013, 135, 13322–13325. (DOI:10.1021/ja407648d)

   • Highlighted in JACS Spotlights. J. Am. Chem. Soc. 2013, 135, 13611. (DOI: 10.1021/ja4093727)

   Abs Link

   We report here a potassium-induced guanine quadruplex as a supramolecular platform for controlled assembly of electron donor-acceptor systems. A monodisperse, C-4-symmetric octamer of a guanine-perylene-3,4,9,10-bis(dicarboximide) conjugate (GPDI) was prepared in tetrahydrofuran. The two layers of cyclic guanine tetramers have the same direction of rotation, and the PDI moiety between the layers adopts a nearly eclipsed relationship (H-aggregation), as revealed by small- and wide-angle X-ray scattering, NMR spectroscopy, and steady-state UV/vis absorption. Following photoexcitation of the PDI moiety in the quadruplex, charge separation occurs in tau(CS) = 98 +/- 12 ps to give G(+center dot)-PDI-center dot that recombines in tau(CR) = 1.2 +/- 0.2 ns, which is \textgreater100 times longer than that in the monomeric GPDI dyad. The transient absorption spectrum of G(+center dot)-PDI-center dot within the GPDI quadruplex suggests the formation of a radical anion delocalized over the neighboring PDI units, and this result is consistent with the more favorable electrochemical reduction potential for PDIs in the quadruplex relative to the monomer.

2012

1. 1,1-Dicyano-4-[4-(diethylamino)phenyl]buta-1,3-dienes: Structure-Property Relationships

   Francesca Tancini, Yi-Lin Wu, W. Bernd Schweizer, Jean-Paul Gisselbrecht, Corinne Boudon, Peter D. Jarowski, Marten T. Beels, Ivan Biaggio, and Francois Diederich

   Eur. J. Org. Chem. 2012, 2012, 2756–2765. (DOI:10.1002/ejoc.201200111)

   Abs Link

   We report the synthesis and phys. study of a series of 1,1-dicyano-4-[4-(diethylamino)phenyl]buta-1,3-dienes in which the no. and position of addnl. CN substituents along the 1,1-dicyanobuta-1,3-dienyl fragment is systematically varied. While X-ray anal. provided unambiguous information about mol. geometries in the crystal, UV/Vis and electrochem. measurements, by cyclic voltammetry (CV) and rotating disk voltammetry (RDV), revealed that introduction of addnl. cyano groups in the C2- and C4-positions most affected the optical properties of these mols. in soln., in terms of intramol. charge-transfer absorption energy and intensity. A comparison with structurally related chromophores indicates that the shift of the anilino donor from position 2/3 to 4 along the butadiene scaffold results in a remarkable bathochromic shift of the ICT absorption maxima, mainly due to the higher planarity in the present series. These findings are further corroborated by d. functional theory calcns. Preliminary nonlinear optical (NLO) measurements confirm the promise of the new push-pull chromophores as third-order nonlinear-optical mol. materials. [on SciFinder(R)]

2. 1,2-Di(phenylethynyl)ethenes with axially chiral, 2,2’-bridged 1,1’-binaphthyl substituents: potent cholesteric liquid-crystal inducers

   Yi-Lin Wu, Fiammetta Ferroni, Silvia Pieraccini, W. Bernd Schweizer, Brian B. Frank, Gian Piero Spada, and Francois Diederich

   Org. Biomol. Chem. 2012, 10, 8016–8026. (DOI:10.1039/c2ob25983d)

   Abs Link

   Axially chiral, 3,5-dihydro-4H-dinaphtho[2,1-c:1’,2’-e]azepine (dinaphthazepine) and 1,1’-binaphthyl-2,2’-disulfonimide (dinaphthosulfonimide) moieties were rigidly connected via N-p-phenylene linkers to photochem. (E)/(Z)-isomerizable 1,2-diethynylethene scaffolds. The chem. stability of the resulting systems was found to be critically related to the other substituents on the central π-conjugated scaffold. High helical twisting power (HTP), up to 315 μm-1, for the induction of a cholesteric liq.-cryst. phase through doping of a nematic phase was measured, resulting from the introduction of the chiral, mesogenic 1,1’-binaphthyl motifs. Single crystal X-ray anal. revealed that the phenylene spacer is in π-conjugation with the N-atom of the dinaphthazepine but not with the N-atom of the dinaphthosulfonimide moiety. This difference in orientation results in visible-transparency in the electronic absorption spectrum and higher (E)/(Z)-photoisomerization quantum yields of the dinaphthosulfonimide-derived chiral dopants, as compared to the dinaphthazepine systems, which feature intramol. charge-transfer absorption in the visible region. [on SciFinder(R)]

3. Proacetylenic Reactivity of a Push-Pull Buta-1,2,3-triene: New Chromophores and Supramolecular Systems

   Yi-Lin Wu, Francesca Tancini, W. Bernd Schweizer, Daniela Paunescu, Corinne Boudon, Jean-Paul Gisselbrecht, Peter D. Jarowski, Enrico Dalcanale, and Francois Diederich

   Chem. Asian J. 2012, 7, 1185–1190. (DOI:10.1002/asia.201100997)

   Abs Link

   Herein, we describe the synthesis of a new donor-acceptor-substituted butatriene and demonstrate the chameleonic reactivity of its central CC bond with respect to cycloaddns., undergoing both olefin-type and acetylene-type transformations. The opto-electronic and mol. recognition properties of the resulting new chromophores are discussed. We demonstrated the acetylene-like reactivity of a push-pull bis(4-dimethylaminophenyl) butatriene dinitrile in a formal [2+2] cycloaddn.-cycloreversion reaction to give a zwitterion, in which charges are sepd. through cross-conjugation and stabilized by dimethylaminophenyl (DMA) rings (cation) and cyano groups (allyl anion). The pos. charge on the DMA rings, and in particular their NMe2 centers, is evidenced by complexation with a tetraphosphonate cavitand. The startling and unexpected optical similarity between squaraines and a product, formed via a cumulene-like cyclodimerization of butatriene, indicates the potential application of push-pull [4]radialenes as a new class of dyes with absorptions close to or in the NIR, but with lower polarity and higher soly. [on SciFinder(R)]

4. Structural, Optical, and Electrochemical Properties of Three-Dimensional Push-Pull Corannulenes

   Yi-Lin Wu, Mihaiela C. Stuparu, Corinne Boudon, Jean-Paul Gisselbrecht, W. Bernd Schweizer, Kim K. Baldridge, Jay S. Siegel, and Francois Diederich

   J. Org. Chem. 2012, 77, 11014–11026. (DOI:10.1021/jo302217n)

   Abs Link

   Electrochem. active corannulene derivs. with various nos. of electron-donating 4-(N,N-dimethylamino)phenylethynyl (1-4) or electron-withdrawing cyanobutadienyl peripheral substituents (5-8) were prepd. The latter derivs. resulted from formal [2 + 2] cycloaddn. of cyanoolefins to 1-4 followed by retro-electrocyclization. Conformational properties were examd. by variable-temp. NMR and X-ray diffraction and opto-electronic properties by electronic absorption/emission spectra and electrochem. measurements; these analyses were corroborated by dispersion-cor. d. functional calcns. at the level of B97-D/def2-TZVPP. In CH2Cl2, 1-4 exhibit intramol. charge-transfer (ICT) absorptions at 350-550 nm and green (λem ∼ 540 nm) or orange (600 nm) fluorescence with high quantum yields (56-98%) and are more readily reduced than corannulene by up to 490 mV. The variation of optical gap and redox potentials of 1-4 does not correlate with the no. of substituents. Cyanobutadienyl corannulenes 5-8 show red-shifted ICT absorptions with end-absorptions approaching 800 nm. Intersubstituent interactions lead to distortions of the corannulene core and lower the mol. symmetry. NMR, X-ray, and computational studies on 5 and 8 with one cyanobutadienyl substituent suggested the formation of intermol. corannulene dimers. Bowl-inversion barriers around ΔG‡ = 10-11 kcal/mol were detd. for these two mols. [on SciFinder(R)]

2011

1. Donor-substituted octacyano[4]dendralenes: a new class of cyano-rich non-planar organic acceptors

   Benjamin Breiten, Yi-Lin Wu, Peter D. Jarowski, Jean-Paul Gisselbrecht, Corinne Boudon, Markus Griesser, Christine Onitsch, Georg Gescheidt, W. Bernd Schweizer, Nicolle Langer, Christian Lennartz, and François Diederich

   Chem. Sci. 2011, 2, 88–93. (DOI:10.1039/c0sc00387e)

   Abs Link

   Double [2+2] cycloaddition/retro-electrocyclisation reactions between tetracyanoethene (TCNE) and various anilino-capped buta-1,3-diynes furnished a series of octacyano[4]dendralene derivatives featuring intense, low-energy intramolecular charge-transfer absorptions. These novel chromophores are strong electron acceptors and undergo facile one-electron reductions at potentials (-0.09 to -0.17 eV vs. Fc(+)/Fc, in CH(2)Cl(2)-0.1 M (n)Bu(4)NPF(6)) lower than those reported for the benchmark organic acceptors, such as TCNE (-0.32 eV) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) (-0.25 eV). The electron-accepting power of one octacyano[4]dendralene, as expressed by the computed adiabatic electron affinity (EA), compares to that of the reference acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)-TCNQ) used as a p-type dopant in organic light-emitting diodes (OLEDs) and solar cells. Gas-phase density functional theory (DFT) calculations predict a stretched-out conformation as the global energy minimum for octacyano[4]dendralenes. In the solid state however, folded conformations were observed for two structures by X-ray analysis. Taking the solid state environment approximately into account calculations predict a energetical degeneracy between the stretched-out and folded conformation. Therefore conformational preference probably is a result of supramolecular dimer formation, mediated by two pairs of intermolecular, antiparallel dipolar CN center dot center dot center dot CN interactions.

2010

1. Proaromaticity: organic Charge-Transfer Chromophores with Small HOMO-LUMO Gaps

   Yi-Lin Wu, Filip Bures, Peter D. Jarowski, W. Bernd Schweizer, Corinne Boudon, Jean-Paul Gisselbrecht, and Francois Diederich

   Chem. Eur. J. 2010, 16, 9592–9605. (DOI:10.1002/chem.201001051)

   • Highlighted in Synfacts 2010, 11, 1242. (DOI: 10.1055/s-0030-1258729)

   Abs Link

   Novel donor- and/or acceptor-substituted cross-conjugated carbocycles based on quinoids or expanded quinoids, with radiaannulene perimeters, were prepd. and studied to validate proaromaticity as a concept for reducing HOMO-LUMO gaps in push-pull chromophores. Analyses of IR, 1H NMR, and UV/Vis/NIR spectra in conjunction with mol. structures detd. by x-ray diffraction show that these push-pull quinoids have significant charge-sepd. ground states. This feature results in small optical gaps (near IR region) and diatropic magnetic environments inside the carbocycles, as suggested by nucleus-independent chem. shift (NICS) calcns. The NICS results, together with the bond-length anal. of the quinoid spacers, provide strong support that proaromaticity, i.e., aromatized zwitterionic mesomeric contributions in the ground state, is effective. A push-pull tetrakis(ethynediyl)-expanded quinoid chromophore represents the first proarom. radiaannulene. [on SciFinder(R)]

2. The Search for Tricyanomethane (Cyanoform)

   Dubravka Sisak, Lynne B. McCusker, Andreas Buckl, Georg Wuitschik, Yi-Lin Wu, W. Bernd Schweizer, and Jack D. Dunitz

   Chem. - Eur. J. 2010, 16, 7224–7230. (DOI:10.1002/chem.201000559)

   • Referenced in Wikipedia: Cyanoform

   Abs Link

   Although listed in org. chem. textbooks as one of the strongest carbon acids, and in spite of more than a hundred years of attempts to prep. the compd., tricyanomethane (cyanoform) has resisted isolation and characterization, either as the carbon-acid 1 or as the dicyanoketenimine tautomer 2. Only in the vapor phase at very low pressure has the compd. been identified from its microwave spectrum. Here we review and partially repeat the preparative work. With the aid of spectroscopic and diffraction methods (including powder diffraction) we have identified some of the products obtained as: hydronium tricyanomethanide (3), (Z)-3-amino-2-cyano-3-iminoacrylimide (4), a co-crystal of 4 with sulfuric acid (or corresponding iminium salt), and an addn. product of 2 with hydrochloric acid (5/6). Quantum-mech. calcns. at the MP2/6-311++g(2d,2p) level have been made to assess the relative energies of some of the mols. involved. [on SciFinder(R)]

3. Mechanistic Investigation of the Dipolar [2+2] Cycloaddition-Cycloreversion Reaction between 4-(N,N-Dimethylamino)phenylacetylene and Arylated 1,1-Dicyanovinyl Derivatives To Form Intramolecular Charge-Transfer Chromophores

   Yi-Lin Wu, Peter D. Jarowski, W. Bernd Schweizer, and Francois Diederich

   Chem. Eur. J. 2010, 16, 202–211. (DOI:10.1002/chem.200902645)

   Abs Link

   The kinetics and mechanism of the formal [2+2] cycloaddn.-cycloreversion reaction between 4-(N,N-dimethylamino)phenylacetylene (1) and para-substituted benzylidenemalononitriles 2 b-2 l to form 2-donor-substituted 1,1-dicyanobuta-1,3-dienes 3 b-3 l via the postulated dicyanocyclobutene intermediates 4 b-4 l have been studied exptl. by the method of initial rates and computationally at the unrestricted B3LYP/6-31G(d) level. The transformations were found to follow bimol., second-order kinetics, with ΔHexp≠ =13-18 kcal mol-1, ΔSexp≠ ≈-30 cal K-1 mol-1, and ΔGexp\vphantom{} ≠-27 kcal mol-1. These exptl. activation parameters for the rate-detg. cycloaddn. step are close to the computational values. The rate consts. show a good linear free energy relationship (ρ=2.0) with the electronic character of the para-substituents on the benzylidene moiety in DMF, which is indicative of a dipolar mechanism. Anal. of the computed structures and their corresponding solvation energies in acetonitrile suggests that the rate-detg. attack of the nucleophilic, terminal alkyne carbon onto the dicyanovinyl electrophile generates a transient zwitterion intermediate with the neg. charge developing as a stabilized malononitrile carbanion. The computational anal. predicted that the cycloreversion of the postulated dicyanocyclobutene intermediate would become rate-detg. for 1,1-dicyanoethene (2 m) as the electrophile. The dicyanocyclobutene 4 m could indeed be isolated as the key intermediate from the reaction between alkyne 1 and 2 m and characterized by X-ray anal. Facile first-order cycloreversion occurred upon further heating, yielding as the sole product the 1,1-dicyanobuta-1,3-diene 3 m. [on SciFinder(R)]

2009

1. Polymeric Ladderphanes

   Chih-Ming Chou, Shern-Long Lee, Chih-Hsien Chen, Akkattu Thankappan Biju, Hsian-Wen Wang, Yi-Lin Wu, Guo-Fu Zhang, Kuang-Wei Yang, Tsong-Shin Lim, Min-Jie Huang, Po-Yu Tsai, Kin-Chuan Lin, Shou-Ling Huang, Chun-hsien Chen, and Tien-Yau Luh

   J. Am. Chem. Soc. 2009, 131, 12579–12585. (DOI:10.1021/ja9035362)

   Abs Link

   A new class of polymers, which have a double-stranded polybinorbornene skeleton with multilayer planar oligoaryl linkers, defined as polymeric ladderphanes, are synthesized. The structures of these ladderphanes are detd. by spectroscopic means. Photophys. studies and time-resolved fluorescence spectroscopic investigations reveal that there is a strong interaction between the chromophore linkers. Thus, Soret band splitting in the absorption spectrum of the polymer with porphyrin linker (12e), significant fluorescence quenching with oligoaryl linkers (12b-d), and excimer emission with a terphenylene-diethynylene linker (12a) are characteristic photophys. properties of these polymers. Scanning tunneling microscopy shows that polymers 12b and d exhibit a ladder-like morphol. and form a supramol. assembly leading to a two-dimensional ordered array on a highly oriented pyrolytic graphite surface. [on SciFinder(R)]

2. Observing Second-Order Nonlinear Optical Properties by Symmetry Breaking in Centrosymmetric Furan-Containing Oligoaryl Cyclophandienes

   Hsin-Chieh Lin, Jui-Hung Hsu, Chao-Kuei Lee, Oliver Yung-Hui Tai, Chin-Hsien Wang, Chih-Ming Chou, Kuang-Yen Chen, Yi-Lin Wu, and Tien-Yau Luh

   Chem. Eur. J. 2009, 15, 13201–13209. (DOI:10.1002/chem.200902115)

   Abs Link

   Centrosym. furan-contg. cyclophandienes 3 and 4, synthesized by our furan annulation protocol, have been shown to exhibit extraordinarily large Stokes shifts and second-order nonlinear optical β values. The β values for 3 and 4 measured at 1.32 μm are 208 and 530×10-30 esu, resp. The β values of 3 and 4 are similar to those of resp. cyclophenes 1 a and 7 in which strong hyperpolarizable interactions between two twisted π-systems (oligoaryl and bridging double bond) might take place. Symmetry breaking due to the resonance contribution (cf. 2) and the unique structural features of 3 and 4 has been used to account for this unusual photophys. behavior. [on SciFinder(R)]

3. New donor-acceptor chromophores by formal [2+2] cycloaddition of donor-substituted alkynes to dicyanovinyl derivatives

   Peter D. Jarowski, Yi-Lin Wu, Corinne Boudon, Jean-Paul Gisselbrecht, Maurice Gross, W. Bernd Schweizer, and Francois Diederich

   Org. Biomol. Chem. 2009, 7, 1312–1322. (DOI:10.1039/b821230a)

   Abs Link

   The efficient methodol. of the cycloaddn. between electron-rich alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), followed by retro-electrocyclization, is extended to dicyanovinyl derivs. to produce new donor-acceptor push-pull 1,1-dicyanobutadienyl chromophores in excellent to quant. yield (63-98%) that express strong charge-transfer (CT) absorptions from 300 to 600 nm. The scope of this reaction is established by both varying the nucleophilic and electrophilic components. Electrochem. studies show that the CT properties of these systems are readily tunable by substitution on the electrophile, which has the largest effect on the LUMO. Non-reversible redn. potentials range from ca.-1.2 to -1.9 V in CH2Cl2, against the ferricinium/ferrocene couple (Fc+/Fc) according to cyclovoltammetry and rotating disk voltammetry. The chromophores show a significant non-planarity between the N,N-dimethylanilino donor and the 1,1-dicyanovinyl acceptor moieties, with torsional angles around 40° from X-ray anal., but retain strong quinoidal character. The mechanism of this reaction has been studied computational using d. functional methods in the gas-phase and using the polarizable continuum model for addressing solvent effects. The complete reaction free-energy profile has been detd. for the reaction of 1,1-dicyanoethene and 4-ethynyl-N,N-dimethylaniline. The process proceeds through formal [2+2] cycloaddn. followed by retro-electrocyclization. The formation of a zwitterionic intermediate in the cycloaddn. step is shown. [on SciFinder(R)]

2008

1. 1,2,3-Triazoles as conjugative π-linkers in push-pull chromophores: Importance of substituent positioning on intramolecular charge-transfer

   Peter D. Jarowski, Yi-Lin Wu, W. Bernd Schweizer, and Francois Diederich

   Org. Lett. 2008, 10, 3347–3350. (DOI:10.1021/ol801253z)

   Abs Link

   Isomeric charge-transfer chromophores using 1,2,3-triazolediyl linkers have been studied exptl. and computationally. The instability of the polarized reactants precluded the use of the Huisgen reaction and alternative synthetic methodologies were employed. Charge-transfer absorptions between an N,N-dimethylanilino and a dicyanovinyl group are modest to strong, with maxima from λmax = 400 to 453 nm depending on substituent positioning. Time-dependent d. functional B3LYP/6-31G(d) calcns. are within 0.6 eV of expt. and assign these bands as HOMO-LUMO transitions. [on SciFinder(R)]

2007

1. Sequential Electrochemical Oxidation of Alternating Benzene-Furan Oligomers

   Cheng-Lan Lin, Yi-Lin Wu, Chang-Li Chen, Chih-Ming Chou, and Tien-Yau Luh

   J. Org. Chem. 2007, 72, 8531–8534. (DOI:10.1021/jo070999+)

   Abs Link

   Electrochem. oxidn. of pentaaryl 2 contg. two furan moieties occurs sequentially to give diketone 8 after two-electron transfer. Further oxidn. with another two-electron transfer gives the corresponding tetraketone 9. Radical cation intermediate is detected by absorption spectroscopy. The radical intermediates of different regiochem. have been shown to exhibit different oxidn. potentials as revealed by the differential pulse voltammetry. [on SciFinder(R)]