Synergistic Photoluminescence Enhancement in Nonaromatic Amino Acids and Sugars via Glycosylation

Abstract

Nonaromatic amino acids with intrinsic photoluminescence (PL) have drawn growing attention due to their crucial role in the luminescence of natural proteins. However, the weak luminescence significantly constrains the study of specific photophysical processes, emission mechanism of biomolecules, and their applications. Here, a serendipitous finding of synergistic PL enhancement by coupling nonaromatic amino acids and sugars via glycosidic bonds is reported. For example, the crystals of glucose, L-serine, alongside their corresponding disaccharide and dipeptide are weakly emissive, while glycosylation drastically boosts the quantum yields of L-serine crystals from 0.3% to as high as 9.2%, accompanied by the emergence of pronounced 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. Furthermore, the ultrafast femtosecond to nanosecond transient absorption spectroscopy and theoretical calculations further reveal the importance of hybridization of locally excited and charge transfer 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.