Photoinduced electron transfer processes in three component rotaxanes with porphyrins, [60]fullerene and triphenylamine

Abstract

Electron transfer processes occurring through-space and through-bond were studied for novel mechanically linked triad [2]rotaxanes, which contain a porphyrin (MP) unit as a pendant and [60]fullerene ( C 60) and triphenylamine ( TPA ) moieties as stopper groups at the axle ends (abbreviated as ( MP ; C 60- TPA ) rot+ with MP = H 2 P or ZnP . The photophysical properties were investigated by means of time-resolved fluorescence and transient absorption measurements with changing solvent polarity. The charge separation took place mainly via(1 MP *; C 60- TPA ) rot+ and ( MP ;1 C 60*- TPA ) rot + in polar solvents. Within the charge-separated states of triads ( MP ; C 60- TPA ) rot +, hole-shift and/or back electron transfer took place competitively. The lifetime of the charge separation state of ( ZnP ; C 60- TPA ) rot+ was similar to that of dyad ( C 60- TPA ) rot+ (140 ns in dimethylformamide), whereas that of ( H 2 P ; C 60- TPA ) rot + was as long as 230 ns, suggesting two final charge separation states such as ( MP ; C 60•-- TPA •+) rot + and ( MP •+; C 60•-- TPA ) rot+ depending on the kind of porphyrin.