Determination of HOMO and LUMO Level of Polythiophene, Poly(3-Thiophene Acetic Acid), Polypyrrole and Chlorophyll via Cyclic Voltammetry Method

Abstract

Cyclic voltammetry can be used to investigate the chemical reactivity of species ion via oxidation and reduction process. The purpose of this study is to determine the level energy of high occupied molecule orbital (HOMO) and low unoccupied molecule orbital (LUMO) in polythiophene (PT), Poly (3-thiophene acetic acid) (P3TAA), polypyrrole (PPY) and chlorophyll (Chlo) through oxidation and reduction of molecular ions by cyclic voltammetry method. PT, P3TAA, PPY and Chlo solutions were prepared in a solvent of acetonitrile at the concentration range of 10-2 to 10-4 M. The current-voltage measurements for these solutions are performed using cyclic voltammetry method on input voltage from -2.0 V to 2.0 V. The working electrode used is indium tin oxide (ITO). The result of voltammogram is showed that the activity of PT species were produced three oxidation and one reduction processes. The formal reduction potential, Eo¢ is 0.83 (positive) meaning that oxidation process was dominant. So that the reaction of PT species was exhibited irreversible electrochemical behavior. The reaction of P3TAA species was exhibited reversible electrochemical behavior, where the range value of oxidation, DEpa and reduction, DEpc were in range of 0.825 V to 1.120 V and -0.230 V to 0.131 V respectively. PYY species reaction was exhibited irreversible electrochemical behavior where two oxidation states occur within -0.145 V to -0.202 V and 0.870 V to 1.63 V respectively. The species activity of Chlo was exhibited irreversible electrochemical behavior where only the oxidation process was obviously appeared at range of 0.80 V to 0.95 V. The LUMO energy levels of PT, P3TAA PPY and Chlo were 5.84 eV, 5.34 eV, 1.10 eV and 3.85 eV respectively, while HOMO energy levels of PT, P3TAA PPY and Chlo were 4.61 eV, 4.25eV, 3.70 eV and 5.93 eV. The average value of energy gap of PT, P3TAA, PPY and Chlo were 1.23 eV, 1.08 eV, 2.23 eV and 1.10 eV respectively.