Electron transfer processes occurring through-space and through-bond were studied for novel mechanically linked triad rotaxanes, which contain a porphyrin (MP) unit as a pendant and fullerene (C60) and triphenylamine (TPA) moieties as stopper groups at the axle ends (abbreviated as (MP;C60-TPA)rot+ with MP = H2P 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 (1MP*; C60-TPA)rol+ and (MP;1C60*- TPA)rot+ in polar solvents. Within the charge-separated states of triads (MP;C60-TPA)rol+, hole-shift and/or back electron transfer took place competitively. The lifetime of the charge separation state of (ZnP;C60-TPA)rol+ was similar to that of dyad (C 60-TPA)rol+ (140 ns in dimethylformamide), whereas that of (H2P;C60-TPA)rol+ was as long as 230 ns, suggesting two final charge separation states such as (MP;C60 •-TPA•+)rot+ and (MP •+;C60•--TPA)rot+ depending on the kind of porphyrin.
- Photoinduced electron transfer
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