Yoshida Naoya, Ishizuka Tomoya, Yofu Katsuyuki, Murakami Masataka, Miyasaki Hiroshi, Okada Tadashi, Nagata Yasushi, Itaya Akira, Cho Hyun Sun, Kim Dongho
Department of Chemistry, Graduate School of Science, Kyoto University, and Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Kyoto, Japan.
Chemistry. 2003 Jun 16;9(12):2854-66. doi: 10.1002/chem.200204588.
A series of zinc(II) porphyrin-imide dyads (ZP-Im), in which an electron donating ZP moiety is directly connected to an electron accepting imide moiety in the meso position, have been prepared for the examination of energy gap dependence of intramolecular electron transfer reactions with large electronic coupling. The nearly perpendicular conformation of the imide moiety towards the porphyrin plane has been revealed by Xray crystal structures. The energy gap for charge separation, 1ZP* - Im --> ZP+ - Im-, is varied by changing the electron accepting imide moiety to cover a range of about 0.8 eV in DMF. Definitive evidence for electron transfer has been obtained in three solvents (toluene, THF, and DMF) through picosecond-femtosecond transient absorption studies, which have allowed us to determine the rates of photoinduced charge separation, 1ZP* - Im --> ZP+ - Im-, and subsequent thermal charge recombination ZP+ - Im- --> ZP - Im. The free-energy gap dependence (energy gap law) has been probed from the normal to the nearly top region for the charge separation rate alone, and only the inverted region for the charge recombination rate. Although both of the energy gap dependencies can be approximately reproduced by means of the simplified semiclassical equation, when we take into consideration the effect of the high frequency vibrations replaced by one mode of averaged frequency, many features, including the effects of solvent polarity and the electron tunneling matrix element on the energy gap law, differ considerably from those of the previously studied porphyrin-quinone systems, which have weaker interchromophore electronic interactions.
一系列锌（II）卟啉 - 酰亚胺二元化合物（ZP - Im）已被制备出来，其中供电子的ZP部分在中位直接与受电子的酰亚胺部分相连，用于研究具有大电子耦合的分子内电子转移反应的能隙依赖性。X射线晶体结构揭示了酰亚胺部分相对于卟啉平面近乎垂直的构象。通过改变受电子的酰亚胺部分，电荷分离的能隙，即(^{1}ZP^{}-Im \to ZP^{+}-Im^{-})，在二甲基甲酰胺（DMF）中变化范围约为0.8 eV。通过皮秒 - 飞秒瞬态吸收研究，在三种溶剂（甲苯、四氢呋喃和DMF）中获得了电子转移的确切证据，这使我们能够确定光诱导电荷分离(^{1}ZP^{}-Im \to ZP^{+}-Im^{-})以及随后热电荷复合(ZP^{+}-Im^{-} \to ZP - Im)的速率。仅针对电荷分离速率，从正常区域到近乎顶部区域探究了自由能隙依赖性（能隙定律），而对于电荷复合速率仅探究了反转区域。尽管通过简化的半经典方程可以大致重现这两种能隙依赖性，但当我们考虑用一种平均频率模式取代高频振动的影响时，包括溶剂极性和电子隧穿矩阵元对能隙定律的影响在内的许多特征，与先前研究的卟啉 - 醌体系有很大不同，后者的发色团间电子相互作用较弱。
