Abstract

The fluorescence excitation spectrum of covalently linked octaethylporphyrin homodimer (OEP)₂ in the mixture of tetrahydrofuran and toluene (3:1) at 4.2 K consists of two subbands that are ascribed to the donor and the acceptor half of the dimer. The distance between the bands (excitonic splitting) is 52 cm⁻¹. The selective laser excitation in the red subband results in a quasiline fluorescence spectrum, similar to that of a monomer. This indicates that due to a large spatial separation of component macrocycles (intercenter distance 1.05 nm) their mutual influence is small and does not change the character of vibronic interactions. In contrast to the red excitation, excitation at the blue side of the two-maximum 0-0 band given no site selection effect and the fluorescence spectrum resembles the one on excitation in the Soret band. Disappearance of quasiline structure is attributed—similarly to the concentrated dye solutions¹—to a nonresonant energy transfer from donor to acceptor half of the dimer. The nonresonant overlap integral includes the mutual overlap of the phonon wings and the overlap of the donor's zero-phonon line with the acceptor's phonon wing and vice versa. The shape of the phonon wing (peak at the distance of 22 cm⁻¹ from the zero phonon line, FWHM = 31 cm⁻¹) has been revealed by spectral hole burning.

© 1994 IEEE