Excited-State Photodynamics of Perylene-Porphyrin Dyads 5 Tuning Light-Harvesting Characteristics via Perylene Substituents, Connection Motif, and Three-Dimensional Architecture

Seven perylene-porphyrin dyads were examined with the goal of identifying those most suitable for components of light-harvesting systems The ideal dyad should exhibit strong absorption by the perylene in the green undergo rapid and efficient excited-state energy transfer from perylene to p in and avoid electron-transfer quenching of the porphyrin excited state by the perylene in the medium of interest Four dyads have different perylenes at the p-position of the ineso-aryl group on the /Inc porphyrin I he most suitable perylene identified in that set was then incorporated at the m- or o-position of the zinc porphyrin affording two other dyads An analogue of the o-substituted architecture was prepared in which the zinc porphyrin was replaced with the free base porphyrin The perylene in each dyad is a monoimide derivative the perylenes differ in attachment of the linker (either via a diphenylethyne linker at the N-imide or an ethynylphenyl linker at the C9 position) and the number (0-3) of 4-tert-butylphenoxy groups (which increase, solubility and slightly alter the electrochemical potentials) In the p-linked dyad the monophenoxy perylene with an N-imide diphenylethyne linker is superior in providing rapid and essentially quantitative energy transfer from excited perylene to /Inc porphyrin with minimal electron-transfer quenching in both toluene and benzonitrile The dyads with the same perylene at the m- or o-position exhibited similar results except for one case the o-linked dyad bearing the zinc porphyrin in benzonitrile where significant excited state quenching is observed this phenomenon is facilitated by close spatial approach of the perylene and porphyrin and the associated thermodyn imic/kinetic enhancement of the electron-transfer process Such quenching does not occur with the free base porphyrin because electron transfer is thermodynamically unfavorable even in the polar medium The p-linked dyad containing a zinc porphyrin attached to a bis(4-tert butylphenoxy)perylene via an ethynylphenyl linker at the C9 position exhibits ultrafast and quantitative energy transfer in toluene the same dyad in ben/onitrile exhibits ultrafast (<05 ps) perylene-to-porphyrin energy transfei rapid (similar to 5 ps) porphyrin-to-perylene electron transfer and fast (similar to 25 ps) charge recombination to the ground state Collectively, this study has identified suitable perylene-wporphyrin constructs for use in light-harvesting applications