金属卟啉分子组装体系中的三线态能量传递

Triplet Energy Transfer in Porphyrin-Based Molecular Assembled System

利用稳态和瞬态光谱技术研究了人工组装锌卟啉(ZnP)-苯桥(BB)-铁卟啉(Fe(Cl)P)超分子体系中给体三线态到受体的能量传递及其机理。结果表明体系中存在着由给体ZnP三线态向受体Fe(Cl)P的超快能量传递过程,在室温和低温下通过激发给体ZnP,其单线态的激发能经由系间窜越过程使其三线态布居,在受体Fe(Cl)P存在的情况下,位于给体三线态的激发能经由桥联分子B传递到受体Fe(Cl)P,室温下传递速率为7.2×105s-1。由于体系中给体到受体之间的空间距离约为2.5nm,由给体-受体直接耦合引起的传递机理可以排除,由桥联分子媒介的超交换机理是该能量传递过程的主要物理机理。

The photophysical properties of porphyrin-based assembled molecular system was investigated using steady-state fluorescence and transient absorption. The obtained results indicate the existence of energy transfer process from the triplet state of donor ZnP to the acceptor Fe （C1）P, mediated by the bridge molecule. At room temperature, the fluorescence of ZnP was quenched dramatically with the presence of acceptor Fe（C1）P, implying the energy transfer between donor and acceptor. By comparison of the triplet state lifetime of ZnP in reference and assembled system, it was observed the excitation energy of donor＇s triplet state is quenched by a factor of 5, and the rate constant for energy transfer is around 7.2×l0^5 s^-1, The temperature dependence of energy transfer rate constant indicates the influence of conformation on the electronic coupling between donor and acceptor mediating by the bridge molecule. Considering the spatial distance between donor and accepter being upto 2.5 nm, it could be concluded that superexchange mechanism via bridge dominates the deactivation of excited triplet state of ZnP in the assembled porphyrin dimer.