Electronic absorption,vibrational spectra,non-linear optical properties,NBO analysis and thermodynamic properties of 9-[(2-hydroxyethoxy) methyl] guanine molecule by density functional method

The Fourier transform infrared (FT-IR) and FT-Raman of 9-(2-hydroxyethoxy) methyl] guanine (9-2HEMG) have been recorded in the regions 4000–100 and 4000–400 cm⁻¹, respectively. A complete assignment and analysis of the fundamental vibrational modes of the molecule were carried out. The observed fundamental modes have been compared with the harmonic vibrational frequencies computed using DFT (B3LYP) method by employing 6-31G(d,p) and 3-21G basis sets. The vibrational studies were interpreted in terms of potential energy distribution. The first order hyperpolarizability (β₀) and related properties (α, μ and Δα) of this molecular system are calculated using B3LYP/6-31G(d,p) method based on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the σ* and π* antibonding orbitals and second-order delocalization energies (E(²⁾) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. UV–vis spectrum of the compound has been recorded and electronic properties such as excitation energies, oscillator strength and wavelength are calculated by TD-DFT and CIS methods using B3LYP/6-31G (d,p) basis set. Molecular electrostatic potential (MEP) and HOMO–LUMO energy levels are also constructed. The thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (C_p,m), standard entropies (S_m) and standard enthalpy changes (H_m) increase with rise in temperature.