Spectroscopy and dynamics of the excited singlet and triplet states of 2,3-, 2,4- and 2,5-difluorobenzaldehyde vapors

Emission and absorption spectra have been measured for 2,3-, 2,4- and 2,5-difluorobenzaldehyde vapors at different temperatures. The observed emission consists of the T₁(n, π*) phosphorescence accompanied by the weak S₁(n, π*) delayed fluorescence for all the molecules. The vibrational analyses of the emission spectra based on the results of the DFT calculations indicate that the observed emission originates from only the stable (anti) conformer. It is inferred from the temperature dependence of the phosphorescence intensity that the T₁(n, π*) → T₂(π, π*) internal conversion and/or the reverse T₁(n, π*) → S₁(n, π*) intersystem crossing contribute to the decrease in the phosphorescence intensity upon increasing temperature. The obtained spectroscopic data include the Raman spectrum of 2,3-difluorobenzaldehyde.