Influence of structural and solvation factors on the photodestruction and efficiency of singlet oxygen generation by luminophores based on iodo- and bromosubstituted zinc(II), cadmium(II) and boron(III) dipyrromethenates

Abstract

A comparative analysis of the influence of the molecular structure and medium properties on the photostability and efficiency of singlet oxygen generation by luminophores based on iodo- and bromosubstituted zinc(II), cadmium(II) and boron(III) dipyrromethenates is presented. It has been established that photodestruction of halogen-substituted complexes [ZnL2], [CdL2], and [BF2L] includes the initial stages of dehalogenation of luminophores and is a process of photosensitization, the efficiency of which depends both on the molecular structure of the chelates and on the medium properties. Based on experimental and literature data, the mechanism of 1O2 generation with the participation of iodo- and bromosubstituted dipyrromethenates [ZnL2], [CdL2] and [BF2L] was proposed and substantiated. It was shown that the indices of photostability and generation of singlet oxygen by heteroligand boron chelates [BF2L] are approximately 33 and 8 times higher, respectively, than the corresponding characteristics of homoligand complexes [ZnL2] and [CdL2]. The influence of the halogenation features is manifested in an increase of the photodegradation efficiency upon the transition from 2-monoiodo- to 3,5-dibromo- and 2,6-dibromosubstituted dipyrromethenates of zinc(II), cadmium(II) and boron(III) due to a decrease in the probability the transition to a triplet excited state and a decrease in the efficiency of singlet oxygen generation. The combination of the high photostability rates and singlet oxygen generation provides a good practical potential for the use of iodo- and bromosubstituted zinc(II), cadmium(II), and boron(III) dipyrromethenates as PDT agents.