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Ultrafast Photoinduced Energy and Electron Transfer in Multi‐Modular Donor–Acceptor Conjugates
Authors:Dr. Mohamed E. El‐Khouly  Dr. Channa A. Wijesinghe  Dr. Vladimir N. Nesterov  Prof. Melvin E. Zandler  Prof. Shunichi Fukuzumi  Prof. Francis D'Souza
Affiliation:1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565‐0871 (Japan), Fax: (+81)?6‐6879‐7370;2. Current address: Department of Chemistry, Faculty of Science, Kafr el‐Sheikh University (Egypt);3. Department of Chemistry, Wichita State University, Wichita, KS 67260‐0051 (USA);4. Department of Chemistry, University of North Texas, 1155 Union Circle, 305070, Denton, TX 76203‐5017 (USA), Fax: (+1)?940‐565‐4318;5. Department of Bioinspired Science, Ewha Womans University, Seoul 120‐750 (Korea)
Abstract:
New multi‐modular donor–acceptor conjugates featuring zinc porphyrin (ZnP), catechol‐chelated boron dipyrrin (BDP), triphenylamine (TPA) and fullerene (C60), or naphthalenediimide (NDI) have been newly designed and synthesized as photosynthetic antenna and reaction‐center mimics. The X‐ray structure of triphenylamine‐BDP is also reported. The wide‐band capturing polyad revealed ultrafast energy‐transfer (kENT=1.0×1012 s?1) from the singlet excited BDP to the covalently linked ZnP owing to close proximity and favorable orientation of the entities. Introducing either fullerene or naphthalenediimide electron acceptors to the TPA‐BDP‐ZnP triad through metal–ligand axial coordination resulted in electron donor–acceptor polyads whose structures were revealed by spectroscopic, electrochemical and computational studies. Excitation of the electron donor, zinc porphyrin resulted in rapid electron‐transfer to coordinated fullerene or naphthalenediimide yielding charge separated ion‐pair species. The measured electron transfer rate constants from femtosecond transient spectral technique in non‐polar toluene were in the range of 5.0×109–3.5×1010 s?1. Stabilization of the charge‐separated state in these multi‐modular donor–acceptor polyads is also observed to certain level.
Keywords:donor–  acceptor systems  electron transfer  energy transfer  fullerene  artificial photosynthesis
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