Phosphorescence excitation spectra of methylbenzaldehydes in durene single crystals: Site structure and effects of deuterium substition

The low-temperature (15 K) laser phosphorescene excitation spectra of 2,4,5-trimethylbenzaldehyde-1h₁ and -1d₁, and 2,5-dimethylbenzaldehyde-1h₁ and -1d₁, each isolated in durene single crystals are presented. Spectra of molecules in each of two different durene crystal sites were obtained. The red shift of the T₁(0.0) bands upon deuteration, is consistent with these bands arising from φφ1 excitations. The red shift of the TMB T₂(0.0) and the blue shift of the DMB T₂(0.0) may reflect the differing electronic configurations of these states (φφ1 or nφ1 respectively) or may be determined by the details of the coupling of T₂ to the underlying T₁ vibronic levels. A broad continuum-like features was observed in the region of T₂. Changes in this feature brought about by deuteration or a change in crystal environment suggest the involvement of both vibronic and crystal-field-induced coupling of T₂ to the underlying T₁ vibronic levels