Abstract
This paper demonstrates the structural and spectral characteristics of conjugated pyrazoles 3-(p-N,N dimethyl aminophenyl)-5-phenyl-1H-pyrazole (DAPP) and 3-(p-nitrophenyl)-5-phenyl-1H-pyrazole (NPP), with particular attention to the influence of functional group on their tautomeric behaviour and energy band gaps. The HOMO-LUMO transitions, frontier molecular orbitals, dipole moment, and electron charges distribution were computed using density functional theory (DFT) for each tautomer. The absorption and transmission spectra were experimentally obtained under certain solutions and concentration. The results showed that functional groups play a significant role in the formation of tautomers. Further, the energy gap for NPP was calculated experimentally and found to be 3.79 eV. The energy gap was increased substantially by replacing nitro group with N,N-dimethylamino group (DAPP) to be 3.99 eV. The theoretical calculations results were completely agreed with the experimental data, and proved for the first time, proton transfer from nitrogen to carbon with loss of aromaticity in pyrazole dye. (C) 2019 Elsevier B.V. All rights reserved.