Highly Efficient Triplet−Triplet Intramolecular Energy Transfer and Enhanced Intersystem Crossing in Rigidly Linked Copper(II) Porphyrin−Free Base Porphyrin Hybrid Dimers

Abstract

Intramolecular energy transfer as well as excited-state relaxation of gable-type copper(II) porphyrin-free base porphyrin dimers, in which the two halves are linked via a benzene or a naphthalene, was studied by transient absorption and fluorescence spectroscopy. Photoexcitation at 532 nm of the dimer gives rise to transient absorption spectra identical to that of triplet−triplet (T−T) absorption in the free base monomer; however, the absorption intensities in the dimers are more than four times larger than that of the monomer, indicating efficient intramolecular energy transfer from the copper porphyrin to the free base counterpart. Presence of pyridine in the dimer solutions decreases the initial optical densities, while the free base monomer shows no change. The decrease is ascribed to competition between energy transfer via triplet manifolds and quenching by pyridine in the excited trip−quartet and/or trip−doublet states of the copper porphyrin moiety. The analysis of the generated yield of the T1 fre...