Synthesis and spectral luminescence properties of 2-aryl-5-methyl-1,3,4-oxadiazoles and zinc(ii) 2-(2-hydroxyphenyl)-5-methyl-1,3,4-oxadiazole complex

Abstract

2-Aryl-5-methyl-1,3,4-oxadiazoles were synthesized by reflux of equimolar amounts of acyl hydrazides with triethyl orthoacetate in o-xylene. The obtained oxadiazoles, except for 2-(2-hydroxyphenyl)-5-methyl-1,3,4-oxadiazole, luminesce with a high quantum yield in polar and nonpolar solvents (λ^fl_max = 300-339 nm, ϕ = 0.11–0.63). 2-(2-Hydroxyphenyl)-5methyl-1,3,4-oxadiazole emits intensely only in highly polar aprotic DMSO (λ^fl_max = 346 nm, φ = 0.15), whereas its chelate complex with Zn^II luminesces in all solvents with a high quantum yield in a longer-wavelength range of the visible spectrum (λ^fl_max = 413–419 nm, φ = 0.36–0.55).