Synthesis,photophysical properties,and application of optical brighteners based on stilbene-oxadiazole derivatives

A series of symmetrical optical brighteners based on stilbene-oxadiazole derivatives were prepared by the simple synthetic route of a condensation reaction between 4,4′-dicarboxystilbene and N,N′-carbonyldiimidazole reagent, forming stilbene 4,4′-ethene-1,2-diyldibenzohydrazide as a key intermediate. The obtained compounds were characterised by analysis of nuclear magnetic resonance, mass spectrometry, and elemental analysis data. The absorption maximum wavelength, fluorescence emission wavelength, and fluorescence quantum yield were measured in N,N-dimethylformamide solution at room temperature, and the fluorescence properties of the prepared compounds in the solid state were observed and measured. The compounds exhibited bluish and greenish fluorescence emission, with the fluorescence quantum yield in the range 0.2–0.8; the effects of substituents on the emission spectra of these compounds were interpreted. The prepared compounds were applied as optical brighteners to polyester and polyamide-6 fabrics at various concentrations, and their CIE whiteness index and fastness properties were studied.