D'Souza Francis, Chitta Raghu, Ohkubo Kei, Tasior Mariusz, Subbaiyan Navaneetha K, Zandler Melvin E, Rogacki Maciek K, Gryko Daniel T, Fukuzumi Shunichi
Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, Kansas 67260-0051, USA.
J Am Chem Soc. 2008 Oct 29;130(43):14263-72. doi: 10.1021/ja804665y. Epub 2008 Oct 7.
The first example of covalently linked free-base corrole-fullerene dyads is reported. In the newly synthesized dyads, the free-energy calculations performed by employing the redox and singlet excited-state energy in both polar and nonpolar solvents suggested the possibility of electron transfer from the excited singlet state of corrole to the fullerene entity. Accordingly, steady-state and time-resolved emission studies revealed efficient fluorescence quenching of the corrole entity in the dyads. Further studies involving femtosecond laser flash photolysis and nanosecond transient absorption studies confirmed electron transfer to be the quenching mechanism, in which the electron-transfer product, the fullerene anion radical, was able to be spectrally characterized. The rate of charge separation, kCS, was found to be on the order of 10(10)-10(11) s(-1), suggesting an efficient photoinduced electron-transfer process. Interestingly, the rate of charge recombination, kCR, was slower by 5 orders of magnitude in nonpolar solvents, cyclohexane and toluene, resulting in a radical ion-pair lasting for several microseconds. Careful analysis of the kinetic and thermodynamic data using the Marcus approach revealed that this novel feature is due to appropriately positioning the energy level of the charge-separated state below the triplet states of either of the donor and acceptor entities in both polar and nonpolar solvents, a feature that was not evident in donor-acceptor dyads constructed using symmetric tetrapyrroles as electron donors.
报道了共价连接的游离碱卟啉-富勒烯二元体系的首个实例。在新合成的二元体系中，通过在极性和非极性溶剂中利用氧化还原和单重激发态能量进行的自由能计算表明，存在从卟啉的激发单重态向富勒烯实体发生电子转移的可能性。相应地，稳态和时间分辨发射研究揭示了二元体系中卟啉实体的有效荧光猝灭。涉及飞秒激光闪光光解和纳秒瞬态吸收研究的进一步研究证实电子转移是猝灭机制，其中电子转移产物富勒烯阴离子自由基能够进行光谱表征。发现电荷分离速率kCS约为10(10)-10(11) s(-1)，表明存在高效的光诱导电子转移过程。有趣的是，在非极性溶剂环己烷和甲苯中，电荷复合速率kCR慢5个数量级，导致自由基离子对持续数微秒。使用Marcus方法对动力学和热力学数据进行仔细分析表明，这一新颖特性是由于在极性和非极性溶剂中，将电荷分离态的能级适当地定位在供体和受体实体的三重态之下，这一特性在以对称四吡咯作为电子供体构建的供体-受体二元体系中并不明显。
