New NIR dyes based on quinolizino [1,9-hi]phenoxazin-6-iminium chlorides: synthesis, photophysics and antifungal activity

Abstract

A series of new quinolizino[1,9-hi]phenoxazinium dyes built on julolidine and naphthalen-l-amine derivatives or anthracen-1-amine were prepared. The N-terminal of these quinolizino[1,9-hi]phenoxazinium chlorides contains aromatic or aliphatic substituents, along with the functionalities such as chloro, hydroxyl and carboxyl. The photophysical behaviour of these compounds was studied in anhydrous ethanol and aqueous medium under acidic and basic conditions. These fluorophores display absorption and emission maxima up to 675 and 712 nm, respectively, can serve as alternative sensing tools in biological assays.All the quinolizino[1,9-hi]phenoxazinium chlorides were evaluated against the yeast Saccharomyces cerevisiae in a broth microdilution assay. It was found that their antifungal activity depended on the substituent at 14-amino position in benzo[a]quinolizino[1,9-hi]phenoxazin-14(5H)-iminium chlorides, and also on the addition of a fused benzene ring, which occurs in naphtho[2,3-a]quinolizino[1,9-hi]phenoxazin-14(51)-iminium chloride. The highest activity, with a MIC of 0.78 mu M, was obtained for benzo[a]quinolizino[1,9-hi]phenoxazin-14(5H)-iminium chloride with a 3-chloropropyl substituent at the 14-amino position of the heterocycle core.