On electronic structure and electronically excited states of sulfines (thione S-oxides)

Abstract

The two lowest-energy n→π* and π→π* type transitions of the parent sulfine were predicted at different levels of theory, such as CASSCF/CASPT2, EOM-CCSD, CIS, TD-HF and TD-DFT. While calculations by singles-only configuration interaction (CIS) and by random phase approximation (TD-HF) methods provided too large transition energies, results obtained by time-dependent density-functional theory (TD-DFT) are close to those of the multiconfigurational CASPT2 method. To characterize the sulfine chromophore, the sulfines of thiopropanal, thioacetone, 2,2,4,4-tetramethyl-3-thioxocyclobutanone, thioadamantanone, thiocyclopropenone, thiocyclopentadienone, thiocyloheptatrienone, 4,4′-dimethylthiobenzophenone and thiofluorenone were calculated by the TD-DFT method. In good agreement with the experimental findings the aliphatic compounds absorb light intensively between 250 and 270 nm in the near-UV region due to π→π* transitions. The experimentally known first intense higher-energy absorption bands of 4,4′-dimethylthiobenzophenone and thiofluorenone sulfines are also well reproduced by TD-DFT.