8-Arylxanthines as clickable fluorescent tags.

8-Arylxanthines have been extensively investigated due to their diverse biological activities. However, despite numerous studies focusing on their synthesis and biological effects, their fluorescence properties have remained largely overlooked. In this study, we demonstrate how the introduction of aromatic substituents can modulate and enhance the photophysical behavior of 8-arylxanthines, revealing their potential as fluorescent imaging tools. Taking into account the rapidly advancing applications of bioorthogonal chemistry, a series of click-active 8-arylxanthines bearing a propargyl functional group were designed and synthesized. Their photophysical and electrochemical properties were systematically evaluated. A lead compound (XN1) was identified that exhibited a high Stokes shift (65 nm) and fluorescence quantum yield (ΦF = 0.962), while showing no significant cytotoxicity across a range of cancer cell lines as well as healthy cells under the tested conditions. Our findings highlight the tunability of xanthine-based fluorophores and suggest that these derivatives hold significant promise for use in fluorescence-based imaging applications.