Abstract:

As the main source of the fluorescence of plant cell walls, lignin is a natural macromolecular fluorescent material. However, the elusive luminescence mechanism and regulation behavior have seriously hindered the high-value application of lignin fluorescence. In this review, the research progress of lignin fluorescence was summarized in terms of the chemical structure and coupling state of lignin fluorophores. Meanwhile, the research strategy for lignin fluorophores and the scientific problems existing in this field were also summarized, respectively. Firstly, due to the inner - filter effect and the existence of fluorescence quenchers in lignin, it was inconclusive to conclude the chemical structure of lignin fluorophores by comparing the fluorescence intensity and emission wavelength between model compounds and lignin. Secondly, it was limited to analyze the chemical structure of lignin fluorophores alone because of the interactions between lignin fluorophores. The real luminescent group of lignin was the aggregation coupling state between these fluorophores. Furthermore, based on the study of lignin microstructure aggregation behavior and aggregation-induced luminescence theory, the effect and mechanism of lignin aggregation behaviors, including inter-and intra-micellar aggregation, on their fluorescence were clarified from macroscopic aspects. Future research should focus on the optimization of the correlation model of lignin aggregation and fluorescence behavior. Meanwhile, the coupling mechanism between lignin fluorophores should be uncovered from the molecular level. Finally, it was believed that lignin fluorescence was not only simply a study of the photophysical property but also a comprehensive investigation including the chemical structure, microstructure regulation and excited-state energy transfer of lignin. There was still a lot of challenging work to get insights into the mechanism of the fluorescence of lignin, which would further promote the study of lignin in other directions.

Key words: biomass, lignin fluorescence, nanostructure, aggregation (effect), functional material

摘要：

木质素是植物细胞壁荧光的主要来源，是一种天然高分子荧光材料，但木质素的荧光机理和调控机制不明确，制约了其荧光特性的高值利用。本文从木质素荧光团化学结构的筛选和木质素荧光团间聚集耦合态的研究两方面出发，系统地综述了木质素荧光的研究现状，并分别对其研究思路和存在的科学问题进行了总结和凝练。分析表明，首先，由于木质素的自吸收效应和荧光淬灭剂的存在，仅从荧光强度和发射波长两方面筛选与真实木质素荧光相近的模型物作为其荧光团的结论存在一定局限性；其次，木质素荧光团间存在相互作用，单独分析木质素荧光团的化学结构意义有限，木质素真实发光基团是这些荧光团间的聚集耦合态；再次，在木质素微结构聚集行为研究和聚集诱导发光理论的基础上，已从宏观层面明确了木质素胶团间和胶团内两种基本聚集行为对其荧光的影响规律和作用机制，今后的研究应完善木质素聚集荧光行为的关联模型，并从微观分子层面深入揭示木质素荧光团间的耦合机制；最后，木质素荧光并非是一个单纯的光物理性质研究，更是一个由木质素化学结构解析、木质素微结构调控、木质素激发态能量转移等多方向交叉形成的综合性课题，揭示木质素荧光机制仍然是一个具有挑战性的工作，进而会对木质素其他方向的研究起到促进作用。

关键词: 生物质, 木质素荧光, 纳米结构, 聚集（作用）, 功能材料