Bis(triphenylamine) derivatives: Structure-dependent photophysical properties and electropolymerization ability

The series of bis(triphenylamine)s consisting of different aromatic central cores has been designed and synthesized. This was done to test the dependence of the electrochemical properties and electropolymerization ability on the central core of bis(triphenylamine). It was observed that the compound containing a 1,3-substituted phenylene core most easily electropolymerize on the electrode surface, while dyes containing thiophene and EDOT cores do not undergo electropolymerization. This was further explained by DFT calculations of SOMO orbitals, which revealed that the amount of charge at the 4′ position of the phenyl rings of the triphenylamine group varies depending on the central aromatic core. Electrochromic properties of obtained polymers were also tested. The polymers containing electron-withdrawing groups change their color from red via brown to blue, while the polymers obtained via electropolymerization of phenylene derivatives exhibited colorless↔brown↔blue transition. Electrochromic parameters, such as color contrast, long-term stability, response times and coloration efficiency were also investigated. It was found that the electropolymerized layer of derivative with benzooxadiazole as a central core exhibited the best long term stability and it was able to switch between neutral and oxidized states over 700 cycles without loss in color contrast. It was also observed that the photophysical properties also depend on the central core of the dye. The compounds containing electron-withdrawing cores were found to exhibit solvatochromic properties, while the shift of the emission maxima with the solvent polarity was smaller for compounds containing phenylene groups and negligible for compounds containing thiophene and EDOT cores.