Synthesis, structure, spectral and luminescence properties of the tetracoordinated diphenylboron and zinc complexes with 1,3,4-oxadiazole and 1,2,4-triazole ligands

Abstract

The new diphenylboron 1c, 2c and zinc 1d, 2d complexes with 2-(2-hydroxyphenyl)-5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole 1a and 1-phenyl-3-methyl-1,2,4-triazole 2a as the chelating ligands and O-ethyl derivatives 1b, 2b of these ligands have been synthesized and their UV–Vis and photoluminescence studied. Molecular structures of the chelate diphenylboron complexes 1c and 2c were determined by X-ray single-crystal diffraction. Spectroscopic properties of all the compounds, including excited state intramolecular proton transfer (ESIPT) rearrangements observed in ligands 1a and 2a were analyzed using DFT and TD DFT calculations. The emission spectra of ligands 1a, 2a contain a moderate intensity band (φ 0.07, 0.19) in DMSO and two low intensity bands (φ 0.002–0.012) in other solvents. 2-(2-Ethoxyphenyl)-5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole 1b and all the complexes exhibit significant fluorescence both in polar and non-polar solvents in the blue region of the spectrum, 1b: φ 0.84–0.96, λflmax 363–406 nm; 1c,d, 2c,d: φ 0.43–0.65, λflmax 429–457 nm. The displayed spectral characteristics make these complexes promising for the use as blue emitters in the design of light-emitting organic diodes.