Optical properties of pyrene and anthracene containing imidazoles: Experimental and theoretical investigations

A series of anthracene and pyrene containing imidazole derivatives have been synthesized and characterized by spectroscopy. Optical absorption and emission properties of the imidazole derivatives were examined in different solvents of varying polarity. The absorption profile remained unchanged on increasing the solvent polarity, while the emission maxima red-shifted progressively. The solvatochromic shifts of the emission spectra were correlated with ET(30), orientation polarizability and Kamlet-Taft. A better correlation obtained for the Kamlet-Taft treatment suggested the involvement of non-specific interactions in the excited state. The TDDFT calculation results suggested a negligible contribution of charge transfer to the optical properties and more planar excited states. The pyrene containing imidazoles showed higher decomposition temperature when compared to the analogous compounds bearing anthracene. Electrochemical data revealed that the pyrene based imidazoles are electron rich than the corresponding anthracene analogs as indicated by their facile oxidation.