Multi-Triphenylamine-Substituted Porphyrin-Fullerene Conjugates as Charge Stabilizing "Antenna-Reaction Center" Mimics

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• 作者：Francis D'Souza ; Suresh Gadde ; D.-M. Shafiqul Islam ; Channa A. Wijesinghe ; Amy L. Schumacher ; Melvin E. Zandler ; Yasuyaki Araki ; Osamu Ito
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：September 6, 2007
• 年：2007
• 卷：111
• 期：35
• 页码：8552 - 8560
• 全文大小：322K
• 年卷期：v.111,no.35(September 6, 2007)
• ISSN：1520-5215

文摘

A new concept of charge stabilization via delocalization of the -cation radical species over the donormacrocycle substituents in a relatively simple donor-acceptor bearing multimodular conjugates is reported. The newly synthesized multimodular systems were composed of three covalently linked triphenylamineentities at the meso position of the porphyrin ring and one fulleropyrrolidine at the fourth meso position.The triphenylamine entities were expected to act as energy transferring antenna units and to enhance theelectron donating ability of both free-base and zinc(II) porphyrin derivatives of these pentads. Appreciableelectronic interactions between the meso-substituted triphenylamine entities and the porphyrin -system wereobserved, and as a consequence, these moieties acted together as an electron-donor while the fullerene moietyacted as an electron-acceptor in the multimodular conjugates. In agreement with the spectral and electrochemicalresults, the computational studies performed by the DFT B3LYP/3-21G(*) method revealed delocalizationof the frontier highest occupied molecular orbital (HOMO) over the triphenylamine entities in addition tothe porphyrin macrocycle. Free-energy calculations suggested that the light-induced processes from the singletexcited state of porphyrins are exothermic in the investigated multimodular conjugates. The occurrence ofphotoinduced charge-separation and charge-recombination processes was confirmed by the combinationof time-resolved fluorescence and nanosecond transient absorption spectral measurements. Charge-separatedstates, on the order of a few microseconds, were observed as a result of the delocalization of the -cationradical species over the porphyrin macrocycle and the meso-substituted triphenylamine entities. The presentstudy successfully demonstrates a novel approach of charge-stabilization in donor-acceptor multimodularconjugates.