Structures and photophysics of lophine and double lophine derivatives

Abstract

Novel lophine (2,4,5-triphenylimidazole) derivatives, ortho-, meta- and para-substituted in the 2-phenyl ring and p-phenyl, p-tolyl, and p-anisyl rings in the 4- and 5-aryl rings and double lophine derivatives were synthesized and their physico-chemical properties were determined. We included arylimidazoles, derivatives substituted with electron-donating and electron attracting groups. MeO- and OH-groups release electrons and activate the ring. In contrast, COOH- and CN-groups withdraw electrons and deactivate the ring. Nitro derivatives of imidazole, phenol, 2-[4,5-bis(4-methoxyphenyl)-1 H-imidazole-2-yl]-4-nitro 23 and phenol, 2-[4,5-bis(4-methyl-phenyl)-1 H-imidazole-2-yl]-4-nitro 24 crystallize with guest molecules in various colors. Double imidazole derivatives of lophine, 2,2′-(2,5-thiophenediyl)bis[4,5-diphenyl-1 H-imidazole] 27 and 2,2′-(1,4-phenylene)bis[4,5-diphenyl-1 H-imidazole] 29 show piezochromism, photochromism and thermochromism in the solid state and form inclusion compounds in various colors. Four inclusion compounds in two different colors: yellow and green, depending on the solvent molecules were found for 27 and two different colors: light yellow and colorless were obtained for 29. The fluorescence intensity for 27 substituted with MeO-group in the 4,5-phenyl rings is decreased and it is increased for 29 by changing phenyl rings to MeO-substituent in the 4,5-phenyl rings. Upon irradiation with UV light at room temperature, green solution of 29 turned into orange and colorless solution of 29 turned into light yellow. The photochemical properties of 27 and 29 and their derivatives were studied by irradiating basic and neutral degassed acetonitrile solutions with medium pressure xenon lamp and their photochemical quantum yields, ranging from 0.0011 to 0.0024, together with the corresponding fluorescence quantum yields, ranging from 0.52 to 0.90 and lifetimes, ranging from 1.03 to 1.42 ns were determined. These compounds are sensitive to different external stimulations, such as UV irradiation, heat, increasing pressure, and changing of the environmental pH, causing spectral changes. Our results suggest potential applications of these compounds in molecular photonics and sensing.