In this contribution, we add theoretical investigations to an experimental study on the photocleavage of coumarin, 6-methylcoumarin, 6-dodecylcoumarin monomers and several syn or anti, head-to-head or head-to-tail isomers. Using a density-functional tight-binding method together with a linear-response extension, we were able to calculate the photoexcitation spectra of all molecules in their optimized geometries. Additional molecular-dynamics simulations of the molecules in the gas phase, gave access to the structural changes due to thermal vibrations and to the influence on the excitation spectra. The sampled photoexcitation spectra are comparable to the experimentally measured data. Moreover, we could show that the dimerization reaction can be monitored by recording the changes of the spectra.
©2014 Walter de Gruyter Berlin/Boston