Spectroscopic and Thermodynamic Studies of Charge- Transfer Complexes Formation Between Cytosine, Uracil and Thymine With Electronic Accepters

Abstract

Charge-transfer complexes of 2, 3-dichloro-5, 6-dicyano-1, 4-benzo quinone (DDQ), 2, 3, 5, 6-tetrabromo-1, 4-benzoquinone (Bromanil) and iodine as electronic acceptors with cytosine, uracil and thymine as electronic donors were studies and their electronic spectra were recorded. In each case one charge-transfer (CT) band was observed and recorded. These spectroscopic investigation make in ethanol solvent at four different temperatures (20, 25, 30 and 35°C). The values of equilibrium constant (KCT), molar extinction coefficient (εCT (, absorption band energy of chargetransfer complexes (hνCT) and the dissociation energy of the charge-transfer complexes excited state (W) were calculated and studied with discussed. The ionization potential of the donors (IP) were calculated and discussed from the charge-transfer complex band lowest energy. Thermodynamic parameters i. e. change in standard free energy (ΔG°), change in standard entropy (ΔS°) and change in standard enthalpy (ΔH°) for all these CT complexes were also calculated and discussed.