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 znbull;+‐C 60bull;‐. 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 60bull;‐. The electron transfer rate constant is −2 × 10 11 s−1.