Tuning of Imidazo[2,1-b][1,3,4]thiadiazole derivatives using electron-donating and electron-withdrawing groups for improving optoelectronic and NLO properties – a computational study

Imidazo[2,1-b][1,3,4]thiadiazole is a promising scaffold for developing optoelectronic materials. In this study, 12 imidazo[2,1-b][1,3,4]thiadiazole derivatives (ITDs) with an A-π1-π2-π3-D architecture have been computationally designed by incorporating four electron-withdrawing diazenyl-thiadiazole groups (R1) with varying numbers of cyano groups and three electron-donating groups (R2), namely pyrene, phenoxazine and diethylamino groups. Their optoelectronic and nonlinear optical (NLO) properties have been investigated computationally at the CAM-B3LYP/6-31++G(d,p) level in chloroform. ITD3d has exhibited the lowest HOMO–LUMO energy gap of 3.25 eV and a red shift of 202 nm in its simulated UV–visible absorption maximum compared with the parent molecule. The diethylamino and 2-(tricyanoethenyl)-5-diazenyl-1,3,4-thiadiazole group have efficiently enhanced the absorption maximum. ITD1d has shown the highest mean linear polarisability <α> in the gas phase and solvent phases, at 106.52 × 10−24 esu and 128.73 × 10−24 esu, respectively. ITD3d has exhibited the highest first-order hyperpolarisability (βtotal) of 957.82 × 10−30 esu and 1243.73 × 10−30 esu ­and mean second-order hyperpolarisability <γ> of 6.83 × 10−33 esu and 11.19 × 10−33 esu in the gas phase and solvent phases, respectively. These findings highlight the potential of the designed ITDs as NLO materials.