Synthesis,characterisation,and study of the photophysical properties of highly stable imidazole-based novel solid-state fluorescent azo colourants

摘要

Novel solid-state fluorescent azo colourants derived from 5-amino-2-(4-dimethylaminophenyl) benzimidazole as electron donor were synthesised. The colourants were characterised by means of elemental analysis, ~1H NMR, and mass spectrometry. These colourants showed molar extinction coefficients in the range 12 000-48 000 dm~3 mol~(-1) cm~(-1). These compounds exhibited solid-state fluorescence under short UV (254 nm). Electron coupling originating from broad π-electron delocalisation and keto-enol form is responsible for the large Stokes shift as indicated by absorption and fluorescence spectra. These colourants were soluble in polar aprotic high-boiling solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulphoxide, whereas they were insoluble in other common organic solvents. Thermogravimetric analysis of solid-state fluorescent colourants showed that two of the colourants showed thermal stability in the range 230-240 ℃, whereas for the rest of the colourants it was found to be lower, and hence the two colourants could find application in the coloration of polymers.