Amino-functionalized nitrothiophenes: A combined computational study of solvation effects, electronic structure, and NLO properties

This study presents an integrated computational investigation of two structurally related thiophene derivatives, 2,4-dinitrothiophene (DNTh) and its amino-functionalized analogue, 2-amino-3,5-dinitrothiophene (ADNTh), with an attempt at explicit understanding effects donor-acceptor engineering can exert on electronic, solvation as well as nonlinear optical (NLO) properties. Theoretical calculations including density functional theory (DFT) and time-dependent DFT (TD-DFT), and molecular dynamics (MD) simulations in conjugation with wavefunction-based descriptions such as NBO, QTAIM, ELF, RDG showed that significant lowering of HOMO-LUMO gap accompanied with strong intramolecular charge transfer (ICT) resulted from amino substitution leading to dramatic enhancement in first-order hyperpolarizability. An increase in both the polarity and possible delocalization of ADNTh was evaluated via electrophilic site maps and density of states analyses. Radial distribution functions and dielectric study have indicated a preferred orientation of hydrogen bonding and increased ordering of the solvent for Acetonitrile. The computed IR, Raman, UV–Vis, photoluminescence, and NMR spectral data showed high correlation with the pertinent experimental measurements, thus proving the approach theoretically valid in this case. Hirshfeld surface analysis further supports enhanced molecular interactions in ADNTh systems. In this context, it can be inferred that intentional donor group substitution highly tunes the optical, electronic, and nonlinear optical properties of π-conjugated heterocyclic systems; thus helping to set up design rules for the rational engineering of advanced functional materials toward photonic devices, organic electronics components, or molecular sensing applications.