Isatin-phenylhydrazone dyes and boron complexes with large Stokes shifts: synthesis and solid-state fluorescence characteristics

Isatin-phenylhydrazone derivatives and their corresponding BF2-complexes were efficiently synthesized by a three-step reaction starting from isatin and phenylhydrazine hydrochloride. The optical properties of these isatin-phenylhydrazone derivatives and their difloroboron complexes were investigated in different organic solvents and in the solid-state. Although these fluorescent dyes exhibit feeble fluorescent intensity in solution-state, high fluorescent intensity can be detected in their solid-state. The Stokes shift of these dyes can be achieved 95-198 nm versus the typical BF2-complexes (ca. 15 nm) in the solid-state, which were caused by the remarkable geometry relaxation upon photoexcitation and its substantial effect on the energy levels of molecular orbitals. Information supporting this inference was supported by the density functional theory calculations. (C) 2015 Published by Elsevier Ltd.