Aggregation and photophysical properties of water-soluble sapphyrins

Aggregation and photophysical properties of three sapphyrins were studied by UV/Vis, emission, resonance light scattering and laser kinetic spectroscopies. The relative abundance of various types of aggregates depends mainly on the structure of sapphyrin, solvent and temperature. The formation of H-dimers is related to negative entropy and enthalpy changes and it is controlled mainly by electrostatic interactions between the positively charged sapphyrin unit and negative substituents. Excitation of the H-dimers leads to the formation of the triplet states of the sapphyrin monomers. The quantum yields of the singlet oxygen in methanol vary between 0.30-0.33 and are independent of substitution. (C) 2004 Elsevier B.V. All rights reserved.