Electrochromism in Electrodeposited Polyamic thin films

Abstract

PAA was chemically synthesized from two starting materials, ODA and PMDA using acetonitrile as solvent. The chemically synthesized product was characterized using FTIR spectroscopy and UV/Vis spectroscopy. PAA was drop coated onto GCE and electrodeposited onto ITO electrode and characterized using electrochemical methods (cyclic voltammetry, square wave voltammetry), UV/Vis and UV/Vis Spectreelectrochemistry. The morphology of the prepared electrodes was studied using scanning electron microscopy (SEM). The electrodeposited PAA thin films were observed to have two redox couples with a formal of 266 mV and -283 mV (vs Ag/AgCI). The diffusion coefficient (De) determined from cyclic voltammetry was found to be 7.9x10-6 cm2/s and provide a measure of how fast charge is transported through the thin film. PAA showed a broad absorption peak at 214 nm due to the carbonyl chromophores within the polymer and shoulder peak at 293 nm from a quinoid-type chromophore. The calculated band gap of 4.23 eV indicated the polymer was optically transparent. Spectro-electrochemistry measurements were performed on the PAA thin films while applying a fixed potential, to evaluate electrochromic properties of the polymer. The polymer itself showed no electrochromic shift, but a decrease in absorbance was observed, as a function of applied potential. PAA was found to be optically transparent between 300 and 800 nm throughout all experiments. The analytical response of anthracene and naphthalene was studied at the ITO/PAA using spectro-electrochemistry. The characteristic analytical absorbance signal for anthracene was clearly identified at 375 nm when ITO/PAA electrode was polarised at -800 mV (vs Ag/AgCI). The calibration curve for anthracene showed a linear response from 4.95x10,4 M to 1.15x10,2 M. The analytical absorbance signal for naphthalene was observed at 225 nm was superimposed on the background absorbance of ITO itself. The calibration curve for naphthalene showed a linear response from 5.66 x 10'3 IV! to 1.07 X 10'2 M. The ITO/PAA showed a low detection limit and high sensitivity for anthracene and naphthalene, making it a suitable platform for spectro-electrochemical analysis of PAHs. The limit of detection was found to be comparable with other previously used methods, HPLC.