Effects of solvent and structure on the photophysical and photochemical properties of dye-onium salts have been studied in this report. It is shown that in solution the ion pairs can exist in such different forms as contact ion pair, solvent-separated ion pair or free solvated ions. Solvent polarity influences not only the spectral properties of different forms, but the equilibrium between them as well, leading to change of physicochemical properties of the ion pairs. Ion pairs with different structure of either dye anion or onium cation have different properties. The greater the thermodynamic driving force, the faster the photoinduced electron transfer reaction is. The ion pair system has been modeled using the Molecular Modeling technique, providing some important information for understanding the physicochemical behaviors of the ion pair systems.

Key words: SOLVENT EFFECT, STRUCTURAL EFFECT, ION PAIRS