Synthesis, characterization and photophysical properties of novel 5,7-disubstituted-1,4-diazepine-2,3-dicarbonitriles

Three 5,7-disubstituted-1,4-diazepine-2,3-dicarbonitriles with bulky 2-(3,5-dibromophenyl)ethenyl, 2-(4- tert -butylphenyl)ethenyl and 2-(3,5-dibenzyloxyphenyl)ethenyl substituents were synthesized and characterized using UV–Vis, MS ES, elemental analysis and NMR spectroscopy. NMR data indicated that diazepine rings of all obtained compounds adopted 6 H -tautomeric form. In addition, trans -isomerism within styryl substituents was observed. Experimental data for diazepine derivative containing 2-(4- tert -butylphenyl)ethenyl substituents were verified by X-ray crystallography. The obtained compounds were subjected to photophysical studies. In the UV–Vis absorption spectra two characteristic bands were found. In the solvatochromic study, the first band maxima were located in the range of 384–418 nm, whereas second band maxima in the range of 313–345 nm. Fluorescence intensity of novel diazepine derivatives was rather low in all solvents used with the values of fluorescence quantum yield Ф F = 10 −4 for 2-(3,5-dibromophenyl)ethenyl, and 10 −5 for 2-(4- tert -butylphenyl)ethenyl and 3,5-(dibenzyloxyphenyl)ethenyl 1,4-diazepine-2,3-dicarbonitriles.