PREPARATION AND PHOTOPHYSICAL STUDIES OF PORPHYRIN‐C₆₀ DYADS

Abstract

Abstract Porphyrin‐C 60 dyads in which the two chromophores are linked by a bicyclic bridge have been synthesized using the Diels‐Alder reaction. The porphyin singlet lifetimes of both the zinc (Pz n ‐C 60 ) and free base (P‐C 60 ) dyads, determined by time‐resolved fluorescence measurements, are ≦17 ps in toluene. This substantial quenching is due to singlet‐singlet energy transfer to C 60 The lifetime of Pzn‐ 1 C 60 is ‐5 ps in toluene, whereas the singlet lifetime of an appropriate C 60 model compound is 1.2 ns. This quenching is attributed to electron transfer to yield P zn bull; +‐C 60 bull; ‐. In toluene, P‐ 1 C 60 is unquenched; the lack of electron transfer is due to unfavorable thermodynamics. In this solvent, a transient state with an absorption maximum at 700 ran and a lifetime of‐10 μs was detected using transient absorption methods. This state was quenched by oxygen, and is assigned to the C 60 triplet. In the more polar benzonitrile, P‐ 1 C 60 underoes photoinduced electron transfer to give P • + ‐C 60 bull; ‐. The electron transfer rate constant is −2 × 10 11 s −1 .