Synthesis of two new azo-azomethines; spectral characterization, crystal structures, computational and fluorescence studies

Abstract

This study describes the preparation, characterization and the photoluminescence properties of novel azo-azomethines (2-{(E)-[(4-ethylphenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol, HL1 and 2-{(E)-[(3-ethylphenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol, HL2 dyes). The dyes were characterized by elemental analysis, spectroscopic studies such as IR, H-1 and C-13 NMR, mass and fluorescence spectra. Molecular structures of the dyes were examined by X-ray diffraction analysis. The molecular structures are mostly similar, differing mainly in the position of the ethyl group and dihedral angles between aromatic rings. X-ray data revealed that both HL1 and HL2 favor phenol-imine tautomer in the solid state. An intramolecular phenol-imine hydrogen bond (O1 center dot center dot center dot N1) were observed in both compounds resulting in a S(6) hydrogen bonding motif. Molecular packing of both compounds are determined by pi center dot center dot center dot pi interactions. Quantum chemical investigation of mentioned molecules were performed by using DFT hybrid function (B3LYP) with 6-31+G(d) basis set. The compounds HL1 and HL2 gave intense light emissions upon irradiation by Ultra-Violet light. The photoluminescence quantum yields and long excited-state lifetimes of the compounds HL1 and HL2 were measured. The azo-azomethine dyes HL1 and HL2 have photoluminestence quantum yields of 34% and 32% and excited-state lifetimes of 3.21 and 2.98 ns, respectively. The photoluminescence intensities and quantum yields of these dyes were dependent on the position of alkyl group on the phenyl ring. (C) 2015 Elsevier B.V. All rights reserved.