Electrochromism Properties of Polyimides Possessing Triphenylamine Moieties with Different Substituents

Abstract

Two diamine monomers with methyl (CH3TPA) and methoxy (OCH3TPA) group substituents in the para position of the triphenylamine (TPA) moiety were synthesized by nucleophilic aromatic substitution using 4-fluoronitrobenzene with p-toluidine and p-anisidine, respectively. From these diamine monomers, electroactive polyimides (PI)s were prepared by the chemical imidization of poly(amic acid) solutions, which were prepared with 4,4′-oxydiphthalic anhydride (ODPA). 1H nuclear magnetic resonance and Fourier transform infrared spectroscopy confirmed that both PIs had been synthesized successfully. The measured inherent viscosity for ODPA-CH3TPA PI and ODPA-OCH3TPA PI was 0.42 and 0.49 dL/g, respectively. The glass transition temperatures for ODPA-CH3TPA PI and ODPA-OCH3PDA PI were 236°C and 238°C, respectively, and the thermal degradation temperature of both PIs was above 390°C. The band gaps of ODPA-CH3PDA and ODPA-OCH3PDA were 3.00 and 2.72 eV, respectively. The oxidation onset potential Eox of ODPA-CH3PDA PI and ODPA-OCH3PDA PI from cyclic voltammetry was 0.73 V and 0.65 V, respectively. The highest occupied molecular orbital and lowest unoccupied molecular orbital values differed according to the groups substituted into the triphenylamine moiety. After applying a voltage, the absorption peak intensity at 723 nm and 752 nm for ODPA-CH3TPA and ODPA-OCH3TPA, respectively, increased. The electrical properties varied according to the chemical structure of synthesized diamines.