화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.139, No.34, 11779-11788, 2017
Rigid, Branched Porphyrin Antennas: Control over Cascades of Unidirectional Energy Funneling and Charge Transfer
Porphyrin arrays consisting of three peripheral Zinc porphyrins (ZnPs) and a central free base porphyrin (H2P)-all rigidly linked to each other serve as light-harvesting antennas as well as electron donors and are flexibly coupled to an electron-accepting C-60 to realize the unidirectional flow of (i) excited-state energy from the ZnPs at the periphery to the H2P, (ii) electrons to C-60, and (iii) holes to H2P and, subsequently, to ZnP. Dynamics following photoexcitation are elucidated by time-resolved transient absorption measurements on the femto-, pico-, nano-, and microsecond time scales and are examined by multiwavelength as well as target analyses. Hereby, full control over the charge shift between H2P and ZnP to convert the (ZnP)(3)-H2P center dot+-C-60(center dot-) charge-separated state into (ZnP)(3)(center dot+)-H2P-C-60(center dot-) charge-separated state is enabled by the solvent polarity: It is deactivated/switched-off in apolar toluene, while in polar benzonitrile it is activated/switched-on. Activating/switching impacts the recovery of the ground state via charge recombination rates, which differ by up to 2 orders of magnitude. All charge-separated states lead to the repopulation of the ground state with dynamics that are placed in the inverted region of the Marcus parabola.