PHOTOINDUCED ELECTRON-TRANSFER IN THE ION-PAIR COMPOUND (XTON) - INFLUENCE OF IONIC ASSOCIATION

The influence of the ionic dissociation equilibrium on the photochemic al and photophysical properties of xanthene dye onium salts (XTOn) was studied. The dissociation constants (K-D) determined by conductivity verify that the ionic association states directly influence the change s in the absorption spectral shape, and the ratio I-532/I-445 reflects the degree of dissociation of the system. The results of static fluor escence quenching and dynamic lifetime quenching experiments demonstra te that the electron transfer of XTOn is mainly intra-ion pair electro n transfer; the quenching rate constants of intra-ion pair electron tr ansfer approach 10(12)-10(13) s(-1) M(-1), which is well above the rat e limit controlled by diffusion. The effects of substituents and solve nts show that the process of electron transfer is controlled by the de gree of association, and the efficiency of photosensitized initiation may be improved further by a shift in the equilibrium.