Nonconventional biomacromolecular luminogens have attracted extensive interest due to their fundamental importance and potential applications in diverse areas. To explore novel luminogens and, moreover, to gain deeper insights into their emission mechanism, we study the emission behaviors of sodium alginate (SA), a natural anionic polysaccharide composed of mannuronic (M) and guluronic acids (G). We find that the luminescence from aqueous SA solutions exhibits distinct concentration enhanced emission and aggregation-induced emission (AIE) characteristics. Meanwhile, the ratio of M/G also matters. Rheological measurements reveal the distinct regimes of the solutions, which are consistent with the observed emission, indicative of strong association between the chain entanglement and emission. Moreover, we observe persistent room temperature phosphorescence (RTP) in the amorphous SA solids, which is a rare case even in pure organic aromatic luminogens. Such unique emission can be remarkably enhanced via coordination with Ca ions. These emission behaviors can be well rationalized by the clustering-triggered emission (CTE) mechanism. Namely, the emission is caused by the electron cloud overlap due to the clustering of oxygen atoms and carboxylate units, together with conformation rigidification. Owing to its biocompatibility, intrinsic emission, and, moreover, persistent RTP, SA shows great potential for anticounterfeiting, encryption, intracellular imaging, and so on.

It is a textbook knowledge that protein photoluminescence stems from the three aromatic amino acid residues of tryptophan(Trp), tyrosine (Tyr), and phenylalanine (Phe), with predominant contributions from Trp. Recently, inspired by the intrinsic emission of nonaromatic amino acids and poly(amino acids) in concentrated solutions and solids, we revisited protein light emission using bovine serum albumin (BSA) as a model. BSA is virtually nonemissive in dilute solutions (≤0.1 mg mL−1), but highly luminescent upon concentration or aggregation, showing unique concentration‐enhanced emission and aggregation‐induced emission (AIE) characteristics. Notably, apart from well‐documented UV luminescence, bright blue emission is clearly observed. Furthermore, persistent room‐temperature phosphorescence (p‐RTP) is achieved even in the amorphous solids under ambient conditions. This visible emission can be rationalized by the clustering‐triggered emission (CTE) mechanism. These findings not only provide an in‐depth understanding of the emissive properties of proteins, but also hold strong implications for further elucidating the basis of tissue autofluorescence.

Intrinsic emission and persistent room temperature phosphorescence from amorphous nonaromatic polymers are observed, which can be well rationalized by the CTE mechanism.