Imidazole-2-thiones derived from novel N-heterocyclic carbenes: synthesis and photophysical properties

A series of 13 novel sulfur adducts of imidazo[1,5- a ]quinolin-1(2 H )- and imidazo[1,5- a ]pyridin-1(2 H )-ylidenes (NHC-thiones) were synthesized. Their optical properties were characterized by means of UV-visible and fluorescent spectroscopies. Time-dependent density functional theory calculations were carried out to analyze the absorption and emission properties of the novel NHC-thiones. Good correspondence between experiment and theory was found, confirming and rationalizing the derived relationships between structure and photophysical properties in the series of newly synthesized compounds.