Electronic Spectra of Porphycenes in Rare Gas and Nitrogen Matrices

Abstract

Fine-line electronic absorption and fluorescence spectra of porphycene and 2,7,12,17-tetra-n-propylporphycene have been measured in low-temperature nitrogen, argon, krypton, and xenon matrices. A well-resolved emission spectrum of porphycene was also obtained in an isotropic glassy matrix using the fluorescence line-narrowing technique. Analysis of the observed matrix spectral shifts enabled the assignment of the origin of the S0−S2 electronic transition. Vibrational frequencies have been obtained for the ground and two lowest excited singlet states. Vibronic and site structure in the region of S0−S1 and S0−S2 electronic transitions of porphycenes have been compared with the corresponding data for porphyrin. Both similarities and differences were observed. In particular, contrary to the case of porphyrin and its derivatives, no site structure was observed in the spectra of porphycenes in xenon and krypton matrices. This was explained by a model that takes into account different positions of the transition moment directions in the two chromophores with respect to the matrix cage. No evidence was obtained for the presence of the cis tautomeric forms of porphycene.