meso-Free BIII Subporphyrins with Electron-donating Groups

Abstract

meso-Free B^III 5,10-bis(p-dimethylaminophenyl)subporphyrins were synthesized. They display red-shifted absorption and fluorescence spectra, bathochromic behaviors in polar solvents, a high fluorescence quantum yield (Φ_F =0.57), and a small HOMO-LUMO gap mainly due to destabilized HOMO as compared with meso-free B^III 5,10-diphenylsubporphyrin. This subporphyrin serves as a nice precursor of various meso-substituted B^III subporphyrins such as B^III meso-nitrosubporphyrin, B^III meso-aminosubporphyrin, and meso-meso' linked B^III azosubporphyrin dimer. Reactions of meso-free B^III subporphyrins with NBS or bis(2,4,6-trimethylpyridine)bromonium hexafluorophosphate gave meso-meso' linked subporphyrin dimers, often as a major product along with meso-bromosubporphyrins.

Keywords: Subporphyrin; charge transfer excited state; dimerization; fluorescence; meso-free.