New dyes based on amino-substituted acridizinium salts--synthesis and exceptional photochemical properties

The novel amino-substituted acridizinium salts 5a and 5b represent a new class of cyanine dyes which exhibit intense color along with efficient fluorescence properties. These dyes show moderate solvatochromism in their absorption and emission spectra. The absorption and emission shifts of the two chromophores display a reasonable correlation with solvent parameters such as donor and acceptor number. It was found that the dyes 5a and 5b interact with DNA, with quenching of the band intensies accompanied with a red shift of the absorption and emission bands. Moreover, irradiation of salts 5a and 5b in the presence of DNA results in DNA damage. Solution photolysis of acridizinium salt 5a gave the head-to-tail dimers as the major products (>95%), whereas the acridizinium salt 5b afforded the anti-head-to-tail dimer along with both head-to-head isomers. The latter are thermally labile and rapidly revert to the monomer.