Phenothiazinium photosensitisers: V. Photobactericidal activities of chromophore-methylated phenothiazinium salts

The synthesis of chromophoric di- and trimethyl derivatives of azure A has been carried out along with the physicochemical profiling of the resulting derivatives. Structure–function relationships of the derivatives are proposed with a view to the development of novel photosensitisers with antimicrobial applications. All derivatives exhibited similar magnitudes of photosensitising efficacy in vitro to the standard dyes, azure A and toluidine blue O, but were generally more lipophilic in nature. Chromophoric methylation furnished more active photoantibacterials compared to the lead compounds, both against Gram-positive and Gram-negative organisms.