Influence of electron-withdrawing substituents on photoelectrochemical surface phenomena at phthalocyanine thin film electrodes

The influence of electron-withdrawing substituents on the photoelectrochemical properties of phthalocyanines is shown in a comparison between hexadecafluorophthalocyaninatozinc(II) (FI6PcZn) and the unsubstituted phthalocyaninatozinc(II) (PcZn). The role of surface states in the photoelectrochemistry of both materials has been investigated by time-resolved photocurrent measurements in the millisecond range. The charging and discharging of surface states could clearly be seen as spikes at the beginning and the end of illumination. Surface states were filled with photogenerated electrons at PcZn and with photogenerated holes at F16PcZn. In the steady state under illumination only cathodic photocurrents were detected at PcZn, while at F16PcZn both cathodic and anodic photocurrents were observed. An adsorption step of electroactive species prior to the charge transfer was derived from the dependence of the steady state photocurrents on the electrolyte concentration for both materials. The concentration dependence of the charging and discharging currents, however, showed that charge transfer from surface states to the electrolyte occurs at PcZn, while at F16PcZn the surface states only represent recombination centres. Copyright (C) 1999 John Wiley & Sons, Ltd.