Effect of light on the poly-3-phenylthiophene properties

The electrochemical and photoelectrochemical behavior of a conducting polymer, poly-3-phenylthiophene (P3PhT), is studied in acetonitrile containing salts of tetrabutylammonium (TBA) and lithium. Like other thiophene polymers, P3PhT may or may not be doped cathodically in the presence of salts of TBA or lithium, respectively. In general, the photoelectrochemical behavior of P3PhT resembles that of polybithiophene and poly-3-methylthiophehe. In particular, P3PhT is photoactivated when exposed to light at negative potentials. Depending on the system in which measurements are taken (in the presence of salts of lithium or TBA), P3PhT undergoes photoelectrochemical undoping or photoelectrochemical cathodic doping, respectively, which is confirmed by measuring electrochemical impedance. However, the photoelectrochemical processes on P3PhT (at least in solutions containing lithium salts) proceed much slower than those on other thiophene polymers we studied earlier. The concentration of doping ions in P3PhT in the presence of lithium salts is higher than that in the presence of TBA salts even in the undoped state. This is due to a specific interaction between Li+ and the phenyl group in P3PhT.