Improving the fluorescence brightness of naphthalimide and nitrobenzoxadiazole dyes with cycloalkylamine auxochromes.

We have installed cycloalkylamino auxochromes on naphthalimide (5a - 5e) and nitrobenzoxadiazole (6a - 6e) dyes. Their photophysical characterization revealed that the cyclobutylamino auxochrome in both dyes (5b and 6b) demonstrated high quantum yield and fluorescence brightness compared to their azetidine counterparts (5 and 6) in aqueous solution. The computational studies were performed to substantiate the experimental photophysical results. Cytotoxicity assay in breast adenocarcinoma (MDA-MB-231) and non-cancerous human embryonic kidney 293 (HEK-293) cells indicated significant biocompatibility of cyclobutylamino auxochrome. Moreover, cellular imaging and photostability experiments demonstrated the practical application of cycloalkylamino auxochromes. [Display omitted] • Cycloalkylamine substituted naphthalimides (5a-5e) and 4-nitrobenzoxadiazole (6a-6e) were synthesized and compared with azetidine substituted counterparts (5 and 6) for their fluorescent properties. • Cyclobutylaminated derivatives of naphthalimides and 4-nitrobenzoxadiazole (5b and 6b) show enhanced quantum yields and fluorescence brightness in comparison to their azetidine counterparts (5 and 6). • Compounds 5b and 6b show better biocompatibility and excellent cell penetration in MDA-MB-231 breast cancer cells than their reference standards (5 and 6). [ABSTRACT FROM AUTHOR]