Spectroscopic investigation of some electron withdrawing groups substituted TTF donor.

The structure optimization and spectroscopic properties for some derivatives of tetrathiafulvalene in both the neutral and ionized forms have been studied. The electron withdrawing groups like -CN, -CF3 and -CO2Me were considered to study the effect on structure, vibrational and electronic properties of tetrathiafulvalene. All the calculations were carried out at density functional theory incorporated with B3LYP exchange functional. The CAM-B3LYP exchange-correlation energy functional was also assessed for the determination of molecular structures. The normal coordinate analysis was performed to compute potential energy distributions of the normal modes which were used for the subsequent normal modes assignment. The temperature dependent Raman spectra have been presented showing the relative reduction in Raman intensity. The ionization of TTF-CN leads a very interesting effect. The IR spectrum of neutral TTF-CN contains a very strong CN stretching band at 2251 cm-1 while it is completely diminished in IR spectrum of TTF-CN cation. NBO analyses were also performed to study the electronic structure, second order perturbation and HOMO-LUMO and their energies. Some important thermodynamical parameters have been presented in which entropy calculation reveals below 50% contribution of vibrational motion in all the three molecules.