Inter- and intramolecular photoinduced electron transfer of flavin derivatives with extremely small reorganization energies.
Inter- and intramolecular photoinduced electron transfer of flavin derivatives with extremely small reorganization energies.
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DOI：
10.1002/chem.200903236
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发表时间：
2010-07
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影响因子：
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通讯作者：
M. Murakami;K. Ohkubo;S. Fukuzumi
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文献类型：
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作者：
M. Murakami;K. Ohkubo;S. Fukuzumi
用Marcus光诱导电子转移理论研究了一系列芳香电子给体（D）与黄素类似物（10-甲基异咯嗪：MeFl）单重态或三重态激发态的光诱导电子转移（ET）以及MeFl（*-）与D（*+）在苯甲腈（PhCN）中的分子间反电子转移（BET）。用荧光猝灭法和三重态-三重态（T-T）吸收增强衰减法分别测定了D分子间光诱导ET（k（et））到单重态（1）MeFl*）和三重态（3）MeFl*）的速率常数。k（et）值随着ET驱动力的增加而增加，以达到随着ET驱动力的进一步增加而保持恒定的扩散极限值。利用纳秒激光闪光光解法测定了MeFl（*-）在PhCN溶液中分子间BET反应的速率常数（k（bet））。与k（et）的情况相反，k（bet）的驱动力依赖性显示出朝向高放热区域的显著降低。分子间BET的重组能（λ）通过在反转区域中应用Marcus方程确定为0.68 eV，其中k（bet）值随着BET驱动力的增加而减小。对于从MeFl（*-）到N，N-二甲基苯胺自由基阳离子（DMA（*+））的BET，观察到最慢的BET，其中k（bet）值为3.5 x 10（6）M（-1）s（-1），其比在PhCN中的扩散速率常数（5.6 x 10（9）M（-1）s（-1））小1600倍。然后，将DMA连接到异咯嗪的10位以合成DMA-黄素连接的二联体（10-[4 ′-（N，N-二甲基氨基）苯基]-异咯嗪：DMA-F1）。DMA-F1的光激发导致光诱导ET从DMA部分到F1部分的单重激发态，以形成电荷分离（CS）态（DMA（*+）-F1（*-）），其在298 K下在PhCN中具有极长的寿命（2.1 ms）。
Photoinduced electron transfer (ET) of a series of aromatic electron donors (D) to the singlet or triplet excited state of a flavin analogue (10-methylisoalloxazine: MeFl) and intermolecular back electron transfer (BET) from MeFl(*-) to D(*+) in benzonitrile (PhCN) has been investigated in light of the Marcus theory of ET. The rate constants of intermolecular photoinduced ET (k(et)) from D to the singlet excited state ((1)MeFl*) and the triplet excited state ((3)MeFl*) were determined by fluorescence quenching and enhanced decay rates of triplet-triplet (T-T) absorption by the presence of D, respectively. The k(et) values increase with an increase in the ET driving force to reach the diffusion-limit value that remains constant with a further increase in the ET driving force. Nanosecond laser flash photolysis was performed to determine the rate constants of intermolecular BET (k(bet)) from MeFl(*-) to D(*+) in PhCN. In contrast to the case of k(et), the driving force dependence of k(bet) shows a pronounced decrease towards the highly exothermic region. The reorganization energy (lambda) of intermolecular BET is determined to be 0.68 eV by applying the Marcus equation in the inverted region, where the k(bet) value decreases with increasing the BET driving force. The slowest BET was observed for BET from MeFl(*-) to N,N-dimethylaniline radical cation (DMA(*+)) with the k(bet) value of 3.5 x 10(6) M(-1) s(-1), which is 1600 times smaller than the diffusion rate constant in PhCN (5.6 x 10(9) M(-1) s(-1)). Then, DMA was linked to the 10-position of isoalloxazine to synthesize a DMA-flavin linked dyad (10-[4'-(N,N-dimethylamino)phenyl]-isoalloxazine: DMA-Fl). Photoexcitation of DMA-Fl results in photoinduced ET from the DMA moiety to the singlet excited state of Fl moiety to form the charge-separated (CS) state (DMA(*+)-Fl(*-)) that has an extremely long lifetime (2.1 ms) in PhCN at 298 K.