Effect of ring substituents on the fluorescence spectra of substituted diarylcarbenes

Abstract

The fluorescence spectra of a series of ring-substituted diarylcarbenes have been examined. The solution spectra are generally red shifted by 25–30 nm with respect to the band positions in matrices at 77 K. The difference is believed to reflect emission from non-relaxed conformations at 77 K. Both electron-withdrawing and -donating substituents lead to red shifts in the emission. These shifts are essentially additive, and the carbene emission data show an excellent correlation with free radical fluorescence data for the corresponding diarylmethyl radicals. The temperature dependence of excited carbene lifetimes have been examined for a few representative examples.