Preparation, Characterization, and Electronic Structure of Asymmetric Isonaphthalimide: Mechanism of Dual Fluorescence in Solid State

The asymmetric isonaphthalene imide, 3-[(4-nitrophenyl)­imino]-1H,3H-benzo­[de]­isochromen-1-one was obtained by condensation of 1,8-naphthoylchloride with p-nitroaniline in the presence of pyridine. The crystal structure and vibrational and electronic absorption spectra are reported. The emission spectrum of the crystalline phase demonstrates dual luminescence, with short and long wavelength components, while only the short wavelength component is present in chloroform solution. The geometrical and electronic structures of the ground and excited states of the molecule are investigated using density functional theory methods. Dual fluorescence is explained in terms of the excited states of different nature. The spectroscopic properties of newly synthesized compounds for possible biosensor applications are discussed.