Spectral character of intermediate state in solid-state photoarrangement of α-santonin

The vibronically resolved spectra of an intermediate and a product involved in the photoreaction of α-santonin have been explored by the density functional theory and the post-SCF methodologies, and a detailed comparison of theory with experiment was conducted to obtain reliable assignments to the observed spectra. The predicted emission energies of photosantonic acid and a topochemical product are found to match with the experimental values reasonably. The further calculations manifest that the absorption spectrum of photosantonic acid exhibits vibrationally resolved features, while the absorption band of topochemical product without vibrational resolution is opposite to the experimental observation. These new computational findings lead to a revised assignment to the observed bands and provide a basis for experimentalists to draw a convinced reaction mechanism for the α-santonin photorearrangement.

Highlights► Simulations of vibronically resolved spectra of molecules derived from α-santonin photoreactions. ► The computed emission energy of photosantonic acid agrees well with the experimental value. ► Its absorption spectrum exhibits a vibrationally resolved fashion. ► These findings correct the previous spectral assignment.