4,5-Diaminophthalimides: highly efficient solid-state fluorophores and turn-on type fluorescent probes for hydrazine

Abstract

We report herein that 4,5-bis(diarylamino)phthalimides exhibit efficient solid-state emission. The phthalimides were easily prepared from dimethyl 4,5-bis(diarylamino)phthalates or commercially available 4,5-dichlorophthalic acid via a few steps. The absorption spectra of the phthalimides in toluene showed strong bands at 337–374 nm and weak bands possessing two shoulders at 378–455 nm. Toluene solutions of the phthalimides fluoresced in the greenish blue to orange-yellow region with good-to-high quantum yields. In contrast, the phthalimides showed no emission in DMSO. Based on the observation, phthalimide was demonstrated to serve as a turn-on type fluorescent probe for hydrazine. The phthalimides dispersed in a thin film of poly(methyl methacrylate) and in powder form fluoresced in the blue-to-green and green-to-orange region, respectively, with high quantum yields. As the electron-donating ability of the diarylamino moieties increased, the emission spectra in solution and the solid states were red-shifted. The density functional theory calculations confirm that the photo-excitation involves an intramolecular charge transfer from diarylamino groups to imide-carbonyl moieties.