New and efficient arrays for photoinduced charge separation based on perylene bisimide and corroles

The bichromophoric systems C2-PI, C3-PI, and C3-PPI consisting of corrole and perylene bisimide units and representing one of the rare cases of elaborate structures based on corrole, have been synthesized. Corroles C2 and C3 are, respectively, meso-substituted corroles with 2,6-dichlorophenyl and pentafluorophenyl substituents at the 5 and 15 positions. The three dyads were prepared by divergent strategy with the corrole-forming reaction as the last step of the sequence. C2-PI and C3-PI differ in the nature of the corroles, whereas C3-PI differs from C3-PPI in the presence of a further phenyl unit in the linker between photoactive units. The dyads display spectroscopic properties which are the superposition of the component spectra, indicating a very weak electronic coupling. Excitation of the corrole unit leads to charge separation with a rate which decreases from 2.4 x 10(10), to 5.0 x 10(9), and to 4.9 x 10(7) s(-1) for C2-PI, C3-PI, and C3-PPI, respectively, where the reaction is characterized by a delta G degrees >0. Excitation of the perylene bisimide unit is followed by competing reactions of: 1) energy transfer to the corrole unit, which subsequently deactivates to the charge-separated state and; 2) electron transfer to directly form the charge-separated state. The ratio of electron-to-energy-transfer rates is 9:1 and 1:1 for C3-PI and C3-PPI, respectively. The yield of charge separation is essentially 100 % for C2-PI and C3-PI, and approximately 50 % (excitation of peryleneimide) or 15 % (excitation of the corrole) for C3-PPI. The lifetime of the charge-separated state, observed for the first time in corrole-based structures, is 540 ps for C2-PI, 2.5 ns for C3-PI, and 24 ns for C3-PPI, respectively. This is in agreement with an inverted behavior, according to Marcus theory.