Naphthalimide-cyclophosphazene combination: Synthesis, crystal structure, photophysics and solid-state fluorescence

Abstract

New fluorophore molecules based on combination of naphthalimide and phosphazene groups (4 and 5) were obtained in high yields via one-step nucleophilic substitution reactions and characterized by spectroscopic methods. Also, crystal structures of 2-[2-(4-hydroxy-phenyl)-ethyl]-benzo[de]isoquinoline-1,3-dione (1) and the novel molecule (5) were determined by single-crystal X-ray diffraction technique. Electronic absorption, steady-state and time resolved fluorescence measurements were performed to determine photophysical properties of the compounds. In addition, their solid-state fluorescence spectra were recorded by using fiber optic system. Their fluorescence properties evidence the excimer emission in the visible region (similar to 460 nm) in solution and solid-state. This excimer emission is attributed to the pi-pi stacking interactions which is further supported from crystal structures of the molecules. Moreover, both compounds exhibited high molar extinction coefficients in solution and moderate fluorescence emission especially in solid-state.