Matrix-isolation infrared spectroscopy of 2,3-, 2,4-, 2,5- and 3,4-difluorobenzaldehydes

Four structural isomers of difluorobenzaldehydes (2,3-, 2,4-, 2,5- and 3,4-difluorobenzaldehydes) have been investigated with matrix-isolation infrared spectroscopy in the 700–1800 cm−1 region, combined with UV irradiation and DFT calculations. Photo-induced rotational isomerism has been observed upon UV irradiation for these difluorobenzaldehydes. Two rotamers (anti and syn) were identified upon the photoexcitation and the observed infrared bands of each rotamer have been separated. Based on the infrared data, the energy differences between the anti and syn rotamers have been evaluated in an Ar matrix, which are in good agreement with those obtained by DFT calculations.