Excited state lifetime and intersystem crossing rate of asymmetric pentaazadentate porphyrin-like metal complexes

The first singlet excited state lifetimes (tau(s)) of asymmetric pentaazadentate porphyrin-like complexes, [(R-APPC)M]Cl-n, were measured by the time-correlated single photon counting method. Fluorescent decays of the first singlet excited state for all [(R-APPC)M]Cl-n were found to be shorter than 0.5 ns. The intersystem crossing rates (k(isc)) were calculated from the tau(s) values and previously measured triplet quantum yields (phi(T)). Values for k(isc) for the complexes ranged from 0.68 to 3.04x10(9) s(-1) and are significantly greater than those of silicon naphthalocyanine (SiNc) and lead phthalocyanine (PbPc(CP)(4)). The values of tau(s) and k(isc) of the [(R-APPC)M]Cl-n complexes are sensitive to variations in both the bridging R group and the metal center. (C) 2004 American Institute of Physics.