Glycosylation-Enhanced Luminescence of Nonaromatic Amino Acids

Nonaromatic amino acids with intrinsic photoluminescence (PL) have drawn growing attention due to their crucial role in the luminescence of natural proteins. Nevertheless, the faint luminescence significantly constrains the mechanism exploration of biomolecules as well as their practical applications. We here report a serendipitous finding of synergetic PL enhancement by coupling both weakly emissive nonaromatic amino acids and sugars via glycosidic bonds. Namely, glycosylation drastically boosted the quantum yields of nonaromatic amino acids from 0.3% to as high as 9.2%, accompanied by the emergence of pro-nounced persistent room temperature phosphorescence (p-RTP). This synergistic PL enhancement arises from the ingenious integration of the electron-rich oxygen clusters present in sugar with the charge separation characteristics of amino acids. Driven by amino acids, ample electrons supplied by the sugar rings are directionally induced to promote electron delocaliza-tion, as well as subsequently enhanced absorption, resulting in a more efficient excitation process. Furthermore, the ultrafast femtosecond to nanosecond transient absorption (fs-TA, ns-TA) spectroscopy and theoretical calculations further reveal the importance of hybridization of the locally excited (LE) and the charge transfer (CT) states for PL enhancement and p-RTP features. These results not only provide a universal strategy for constructing efficient nonconventional luminophores but also shed new light on the underlying mechanism of biological autofluorescence.