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 Ca²⁺ 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.

中文翻译：

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海藻酸钠的团簇触发发射和持久室温磷光

非常规生物大分子发光剂由于其基本的重要性和在不同领域的潜在应用而引起了广泛的兴趣。为了探索新型发光剂，并且更深入地了解它们的发射机理，我们研究了藻酸钠（SA）的发射行为，藻酸钠是一种由甘露糖醛酸（M）和古洛糖醛酸（G）组成的天然阴离子多糖。我们发现，SA水溶液的发光表现出明显的浓度增强发射和聚集诱导发射（AIE）特性。同时，M / G的比例也很重要。流变学测量揭示了溶液的不同状态，这与观察到的发射一致，表明链缠结和发射之间有很强的联系。而且，我们观察到非晶态SA固体中存在持续的室温磷光（RTP），即使在纯有机芳香族发光剂中也很少见。通过与Ca的配合，可以显着增强这种独特的发射²⁺离子。这些排放行为可以通过聚类触发排放（CTE）机制很好地合理化。即，发射是由于氧原子和羧酸酯单元的聚集引起的电子云重叠以及构象刚性而引起的。由于其生物相容性，固有发射以及持久的RTP，SA在防伪，加密，细胞内成像等方面显示出巨大的潜力。