Research progress on the luminescence of biomacromolecules

Luminescent materials show great potential in various applications. Traditional aggregation-induced emission (AIE) luminogens are mostly produced by complex organic synthesis and have poor hydrophilicity and biocompatibility, which limit their practical applications. Therefore, it is of great significance to develop fluorescent materials with good hydrophilicity and biocompatibility, and biomacromolecules with these properties have attracted our attention. Partial biomacromolecules can generate unique new fluorophores during the gelation process to obtain hydrogels with good fluorescence properties. In addition, biomacromolecules can be modified with fluorescent groups to obtain fluorescent materials with excellent performance, thus improving the hydrophilicity and biocompatibility of fluorophore. In particular, grafting aggregation-caused quenching (ACQ) luminogens onto biomacromolecules can even effectively inhibit the aggregation and self-quenching of luminogens. It is well known that aromatic biological macromolecules such as green fluorescent protein have intrinsic fluorescence. Intrinsic fluorescence is also observed in nonaromatic biological macromolecules without traditional chromophores such as chitosan, cellulose and sodium alginate. The luminescence of nonaromatic biomacromolecule can be rationalized by the clustering-triggered emission (CTE) mechanism, namely, clustering of nonconventional chromophores and subsequent electron overlap and conformation rigidification are accountable for the emssion. In this review, fluorescence gels obtained from biomacromolecules, biomacromolecules modified with fluorophores, and the intrinsic luminescence of biomacromolecular luminogens are assessed. This review will help to develop low-cost, biocompatible luminescent materials and has great significance for comprehending the luminescence of nonconventional luminophores and expanding the application of luminescent compounds.