Photoinduced electron transfer at liquid/liquid interfaces - Part II. A study of the electron transfer and recombination dynamics by intensity modulated photocurrent spectroscopy (IMPS)

The dynamics of photoresponses associated with heterogeneous quenching of z inc tetrakis(carboxphenyl)porphyrin (ZnTPPC) and ferrocene derivatives at t he water/1,2-dichloroethane interface were studied by intensity modulated p hotocurrent spectroscopy (IMPS). The contribution arising from the electron injection, recombination-product separation competition and the attenuatio n associated with the uncompensated resistance and interfacial capacitance (RC) time constant of the cell were deconvoluted in the frequency domain. T he flux of electron injection was described in terms of a competition betwe en the relaxation of the porphyrin excited state and the electron transfer step. Experimental results in the presence of ferrocene and diferrocenyleth ane confirmed that as the Galvani potential difference is increased, the ph enomenological electron transfer rate constant increases and the ZnTPPC cov erage at the liquid/liquid junction decreases. Furthermore, the recombinati on rate constant decreases with increasing potentials, while the product se paration rate constant did not show a clear potential dependence. Photocurr ent studies were extended to the electron donors dimethylferrocene and tria nisylamine, as well as to the electron acceptor tetracyanoquinodimethane. T he results obtained clearly indicate that the Gibbs energy of activation fo r the charge transfer process is affected by the Galvani potential differen ce. It is suggested that the electron transfer dynamics are dependent on th e local electric held generation by the specifically adsorbed ZnTPPC. The g eneral expressions for the frequency dependent photocurrents at liquid/liqu id interfaces are also introduced.