Electron-donating substituents allow boosted fluorescence emission wavelengths of Dihydropyridopyrazine functionalized xanthene

Abstract

Fluorescent dyes are pivotal tools in biological imaging, environmental sensing, and biomedicine. Long-wavelength dyes, particularly those in the second near-infrared (NIR-II) region, are highly sought after for their enhanced fluorescence quantum yields, excellent photostability, and broad chemical tunability. Despite their potential, systematic strategies for designing such dyes remain limited. In this work, we present an effective approach for extending the emission wavelengths of xanthene-based dyes by replacing the bridging oxygen atom in the heteroanthracene core with various substituents, including -C(CH₃)₂, -Si(CH₃)₂, and -P(O)Ph. These modifications yielded three xanthene-based derivatives with promising NIR-II fluorescence. Theoretical calculations were employed to investigate the structural and electronic properties of the four dyes. Our results reveal that the phosphorus oxide substitution led to a remarkable fluorescence emission at 1864 nm. These findings provide important insights into the design principles for developing second near-infrared fluorescent dyes with potential applications in advanced imaging and sensing technologies.