A comprehensive studies on photophysical and electrochemical properties of novel D-π-A thiophene substituted 1,3,4-oxadiazole derivatives for optoelectronic applications: A computational and experimental approach

Abstract

In the present paper, optoelectronic properties of three newly synthesised thiophene substituted 1,3,4-oxadiazole derivatives namely, Ethyl 4-(5-(5-(4-(4-ethoxycarbonyl (phenyl)) phenyl)-1,3,4-oxadiazol-2-yl) thiophen-2-yl) benzoate [TNO] , 2-(4-(5-(5-hexylthiophen-2-yl)thiophen-2-yl)phenyl)-5-(5-(5-(5-hexylthiophen-2-yl) thiophen-2-yl)thiophen-2-yl)-1,3,4-oxadiazole [TKO] , and 2-(4-(4-vinylphenyl) phenyl)-5-(5-(4-vinylphenyl)thiophen-2-yl)-1,3,4-oxadiazole [TSO] have been explored by a combination of fluorescence spectroscopic techniques and theoretical calculations. The absorption and emission spectra of all the organic fluorescent molecules were recorded in fourteen solvents of different polarity. The ground (µ g ) and excited state dipole moments (µ e ) of all the probes were calculated experimentally by solvatochromic shift method. The ground state dipole moment (μ g ) of all the organic probe molecules in gaseous phase and in different solvents were also estimated theoretically by using the integral equation formalism of polarizable continuum model (IEF-PCM) from ab initio computations by using Gaussian 09 W software and the results are compared. It is observed that, the estimated values of excited state dipole moments are larger than the ground state dipole moments. This suggests that, the redistribution of the electron densities is more polar in excited state than the ground state. Further, the HOMO–LUMO energy level values of all the probes were estimated using Density Functional Theory (DFT). The electrophilic and nucleophilic sites were also recognised with the help of Molecular Electrostatic Potential MESP 3D plots by using TD-DFT computational analysis. The specific and non-specific interactions between the solute–solvent were analysed by multiple linear regression analysis using Kamlet-Abound-Taft and Catalan parameters. Further, the Global Chemical Reactivity Descriptor (GCRD) parameters like, chemical hardness (η), chemical potential (µ), softness (S), electronegativity (χ), and electrophilicity index (ω) were calculated. Electrochemical properties of the probes were investigated (HOMO-LUMO) by using cyclic voltammetry (CV) and is supported by DFT calculations. From the experimental and theoretical observations, we suggest that the organic probe molecules TNO, TKO, and TSO may be considered as potential candidates for OLED, solar cells, chemosensor, and detection of explosives applications in the future.