Sudhakar Kolanu, Gokulnath Sabapathi, Giribabu Lingamallu, Lim Gary N, Trâm Tạ, D'Souza Francis
Inorganic & Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Habsiguda, Hyderabad, 500007, Telangana, India.
Department of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, TX, 76203-5017, USA.
Chem Asian J. 2015 Dec;10(12):2708-19. doi: 10.1002/asia.201500679. Epub 2015 Oct 1.
Closely positioned donor-acceptor pairs facilitate electron- and energy-transfer events, relevant to light energy conversion. Here, a triad system TPACor-C60 , possessing a free-base corrole as central unit that linked the energy donor triphenylamine (TPA) at the meso position and an electron acceptor fullerene (C60) at the β-pyrrole position was newly synthesized, as were the component dyads TPA-Cor and Cor-C60. Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady-state fluorescence studies showed efficient energy transfer from (1) TPA* to the corrole and subsequent electron transfer from (1) corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron-transfer products, the corrole radical cation (Cor(⋅+) in Cor-C60 and TPA-Cor(⋅+) in TPACor-C60) and fullerene radical anion (C60(⋅-)), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, kCS , was found to be about 10(11) s(-1), suggesting the occurrence of an ultrafast charge-separation process. Interestingly, although an order of magnitude slower than kCS , the rate of charge recombination, kCR , was also found to be rapid (kCR ≈10(10) s(-1)), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge-separated species relaxed directly to the ground state in polar solvents while in toluene, formation of (3) corrole* was observed, thus implying that the energy of the charge-separated state in a nonpolar solvent is higher than the energy of (3) corrole* being about 1.52 eV. That is, ultrafast formation of a high-energy charge-separated state in toluene has been achieved in these closely spaced corrole-fullerene donor-acceptor conjugates.
紧密排列的供体 - 受体对有助于与光能转换相关的电子和能量转移过程。在此，新合成了一种三元体系TPACor - C60，它以自由碱卟啉作为中心单元，在中位连接能量供体三苯胺（TPA），在β - 吡咯位置连接电子受体富勒烯（C60），同时还合成了二元组分TPA - Cor和Cor - C60。光谱、电化学和密度泛函理论研究证实了分子的完整性以及各组分之间适度水平的分子内相互作用的存在。稳态荧光研究表明存在从（1）TPA到卟啉的有效能量转移以及随后从（1）卟啉到富勒烯的电子转移。涉及飞秒和纳秒激光闪光光解的进一步研究证实电子转移是卟啉发射猝灭的机制，其中电子转移产物，卟啉自由基阳离子（在Cor - C60中为Cor(⋅+)，在TPACor - C60中为TPA - Cor(⋅+)）和富勒烯自由基阴离子（C60(⋅ -)），可以通过光谱进行表征。由于二元和三元体系中供体和受体实体紧密相邻，电荷分离速率kCS约为10(11) s(-1)，表明发生了超快电荷分离过程。有趣的是，尽管电荷复合速率kCR比kCS慢一个数量级，但也发现其很快（kCR ≈10(10) s(-1)），并且这两个过程都遵循溶剂极性趋势DMF>苯甲腈>四氢呋喃>甲苯。在极性溶剂中，电荷分离物种直接弛豫到基态，而在甲苯中，观察到（3）卟啉的形成，这意味着在非极性溶剂中电荷分离态的能量高于（3）卟啉的能量约1.52 eV。也就是说，在这些紧密间隔的卟啉 - 富勒烯供体 - 受体共轭物中已实现甲苯中高能电荷分离态的超快形成。
