Photoinduced charge separation and recombination in a series of cyclophane-bridged porphyrin-quinone systems (PQ) in toluene solution have been investigated by means of sub-ps time-resolved absorption spectroscopy. Temporal profiles and transient spectra of the porphyrin cation (P+) show the photoinduced formation and decay of the charge-separated state P + Q -. The rate of charge recombination in these systems (P'Q-hPQ) is investigated as a function of the reaction free energy AG in the range (-AG) = 1.54-1.98 eV, which is in the so-called inverted region of electron transfer. Combining values for charge separation and recombination the dependence of the electron transfer rate on AG fully covers the normal and inverted regions ((-AG) = (-)O.OZ-1.98 eV) with the rate varying over more than three orders of magnitude ( = 2. lo9 -5. lo1* s -').
Absorption and emission spectra of the doubly quinone-bridged porphyrin cyclophanes 1–4 with gradually varied acceptor strength as well as of the single-bridged analogues 5–9 and 10–13 are reported. Reduction and oxidation potentials of these intramolecular porphyrin-quinone systems have been determined. Based on these data, fluorescence quenching as well as time-resolved fluorescence lifetime measurements are discussed in terms of photoinduced electron transfer to the charge-separated zwitterionic state
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