Combining Light-Harvesting and Charge Separation in a Self-Assembled Artificial Photosynthetic System Based on Perylenediimide Chromophores

Abstract

Self-assembly of robust perylenediimide chromophores is used to produce an artificial light-harvesting antenna structure that in turn induces self-assembly of a functional special pair that undergoes ultrafast, quantitative charge separation. The structure consists of four 1,7-(3‘,5‘-di-tert-butylphenoxy)perylene-3,4:9,10-perylene-3,4:9,10-bis(carboximide) (PDI) molecules attached to a single 1,7-bis(pyrrolidin-1-yl)perylene-3,4:9,10-perylene-3,4:9,10-bis(carboximide) (5PDI) core, which self-assembles to form (5PDI−PDI₄)₂ in toluene. The system is characterized using both structural methods (NMR, SAXS, mass spectroscopy, and GPC) and photophysical methods (UV−vis, time-resolved fluorescence, and femtosecond transient absorption spectroscopy). Energy transfer from (PDI)₂ to (5PDI)₂ occurs with τ = 21 ps, followed by excited-state symmetry breaking of ^1*(5PDI)₂ to produce 5PDI^•+−5PDI^•- quantitatively with τ = 7 ps. The ion pair recombines with τ = 420 ps. Electron transfer occurs only in the dimeric system and does not occur in the disassembled monomer, thus mimicking both antenna and special pair function in photosynthesis.