Study of molecular structures, electronic properties, spectroscopic analysis and thermodynamic properties of Azulene using first-principles calculations

Abstract

Abstract: Density Functional Theory investigation of Azulene was carried out on the azulene molecule at the B3LYP/6-311G++(d,p) level using Gaussian 09. The optimized geometry confirmed structural stability with consistent bond parameters having the longest bond length of 1.49 Å for C7-C5 shortest bond length of 1.08 Å for C13-H14 and the largest bond angle of 129.89° for C4-C1-C2 indicating slight angular distortion in the carbon framework. The optimized total energy of Azulene is −385.935 Hartree (-10501.291 eV) to be in the optimized geometric structure geometry. The calculated HOMO-LUMO gap with value 3.287 eV agreed well with the density of states having 3.257 eV suggesting that azulene is relatively stable and less prone to electron transfer under normal conditions. Mulliken charge analysis shows that all the hydrogen atoms have positive charges and all of the carbon atom except C5 and C7 corresponds to the negative charge. H8 and H11 exhibit the highest positive charge, while the C1 and C2 exhibit the highest negative charge. The global reactivity descriptors like ionization potential, electron affinity, chemical potential, electronegativity, hardness, softness, and electrophilic index are found to be 5.557 eV, 2.269 eV, -3.931 eV, 3.931 eV, 1.644 eV, 0.608 eV⁻¹ and 4.656 eV respectively. Molecular electrostatic potential, electrostatic potential and electron density analyses revealed distinct electron-rich and electron-deficient regions clarifying the molecule’s reactive sites. Vibrational assignments were consistent with characteristic C-H and C=C modes and thermodynamic parameters demonstrated temperature-dependent increases in heat capacities, internal energy, enthalpy, and entropy, accompanied by a decrease in Gibbs free energy with respect to increase in temperature.