Optical and Electrochemical Properties of Indotricarbocyanine Dyes Promising for Photodynamic Therapy

Abstract

The influence of the molecular structure of indotricarbocyanine dyes on their spectral luminescent and redox properties has been studied. The introduction of a chloro-orthophenylene bridge into the polymethine chain results in a significant hypsochromic shift of the absorption and fluorescence spectra, whereas a change in the substituents structure at the indolenine terminal groups affects the spectra insignificantly. The electrochemical properties of the polymethine dyes have been studied by cyclic voltammetry. The oxidation and reduction potentials of the dyes have been determined and the corresponding energies of the highest occupied and lowest unoccupied molecular orbitals have been calculated. The reduction of the dye molecules is an irreversible process, whereas the reversibility of the oxidation process depends on the structure of the polymethine chain and the nature of the counterion. The introduction of a chloro-ortophenylene bridge into the polymethine chain leads to a significant increase in the reversibility of the oxidation reaction of dyes due to a growth in the stability of dication-radicals. The oxidation of bromide ions has been shown to occur at smaller values of the potential compared to the oxidation of the dyes with substituted polymethine chain, which probably results in a decrease in the reversibility of the electrochemical oxidation of these dyes in the presence of bromide ions in solution.