Computational Study of the Precursor Spectroelectrochemistry of Guanine

Precursor spectroelectrochemical behavior of guanine is investigated based on UV-Vis absorption and fluorescence, and IR and Raman spectra of guanine and its radical cation in the presence of a model electrode, computed using (TD)M06/6-31++G** method. Effects of electrode potential ( ), molecule-electrode distance (d) and molecular orientations (θ) on this behavior are investigated. Results indicate that application of electric potential causes changes in the molecular structure and distribution of charge and spin densities, which consequently changes the electronic and vibrational characteristics of the system. Also, perturbation due to the applied electric potential, changes both the intensities and frequencies of the vibrational bands of the studied species. The absorption wavelength, and the peak intensity and width of the electronic spectra of guanine and its radical cation also show sensitivity to the applied electrode potential. Presence of solvent both as electrostatic medium and as explicit solvent (molecules) have significant effects on the spectroelectrochemical properties of guanine, and change the chemical activity of guanine radical cation formed by the electrode reaction. Furthermore, population and orbital analyses show that for all orientations, application of the electric potential by the electrode increases contribution of the inter-molecular (guanine→water) charge density displacement to the UV-Vis transitions.