Optical properties of novel 2,3-dicyano-5-methyl-6H-1,4-diazepine dyes in the solid state

Novel nonplanar fluorescent dyes, 2,3-dicyano-7-methyl-6H-1,4-diazepines, were synthesized. The fluorescence intensity of 6-substituted 2,3-dicyano-5-[4-(diethylamino)styryl]-7-methyl-6H-1,4-diazepines in vapor-deposited film was on the order of the substituent at the 6-position: n-Bu, Et > t-Bu, H. That of 2,3-dicyano-5-[4-(dialkylainino)styryl]-6-ethyl-7-methyl-6H-1,4-diazepines in the solid state was on the order of the alkyl group: CH2(3,5-(di-tBu)C6H3) > Bn > Et. Thus, the fluorescence intensity in the solid state basically increased with the bulkiness of the substituents on the chromophoric system. X-ray structure analysis clearly showed that the substituent at the 6-position and the dialkylamino moiety should inhibit intermolecular interactions between the chromophores so as to enhance the fluorescence intensity in the solid state.