sustainable afterglow room temperature phosphorescence (RTP) materials, especially afterglow room temperature phosphorescence structural materials, are crucial, but still difficult to achieve. Here, researchers from Nanjing University of Technology & Institute of Chemical Physics, Chinese Academy of Sciences & Northeast Forestry University and other units, developed an oxidation strategy to convert lignin into afterglow material with a lifetime of about 408 ms. Specifically, lignin is oxidized under the action of H2O2 to form aromatic chromophores and fatty acids. The related paper was published in Nature Communications under the title "Structural materials with afterglow room temperature phosphoresce activated by lignon oxidation".
Paper link:
https://www.nature.com/articles/s41467-022-33273-1
Plants are potential sources of renewable chemicals and materials. Lignin is one of its main components, accounting for 15-30% of the total mass, and is formed by the oxidative polymerization of parahydroxycinnamol monophenol produced by the phenylagen pathway. In addition, industrial lignin is a by-product of the pulp and paper industry, with a very large output (about 60-70 metric tons per year). The scientific community has already gained a good understanding of the need for lignin pricing, which has led to a large number of research published in the past few years. From a chemical point of view, lignin is mainly composed of para-hydroxyphenyl (H), guaiacinyl (G) and lilac group (S), and is mainly connected by β-O-4 and C-C bonds. This chemical structure gives lignin great potential as a core component of functional materials and aromatic compounds. In addition, lignin exhibits interesting biological activities, promoting applications in biomedical , agriculture and biomass conversion. Due to the aromatic structure, lignin can produce interesting light physical and chemical properties. Recently, the team of researchers demonstrated that afterglow RTP emission of lignin can be encapsulated in an polyacrylic matrix.
afterglow RTP material has a wide range of applications in electronic devices, optical sensing, biological imaging and information encryption. To achieve effective RTP, two key conditions need to be met. First, by promoting the ISC from S1 to Tn, triplet excitons can be effectively filled. Secondly, non-radiative inactivation of triplet excitons is inhibited and radiation transitions are promoted from the lowest excited state triplet state (T1) to the ground state (S0). So far, small molecules, polymers, supramoleculars, carbon dots and MOFs have been reported for effective afterglow RTP emission. In particular, the preparation of afterglow RTP materials from natural sources is particularly popular because of their abundant, sustainable, flexible and biocompatible nature. However, there are still two main challenges: (1) Converting sustainable lignin to afterglow RTP materials requires the use of petroleum-derived matrix (~95w/w%), which does not meet the requirements of a sustainable system. (2) Most afterglow RTP materials, including lignin source afterglow RTP materials, exist in the form of powder, crystal , thin film, liquid or porous materials. Afterglow RTP structural materials have high mechanical properties and are an important part of material science and technology.
Here, researchers have developed an oxidation method that converts lignin into sustainable afterglow RTP material without adding additional synthetic matrix. Specifically, the G units and S units of lignin are oxidized to form G acid and S acid (chromophore), and then locked by fatty acids (as a matrix, also due to lignin oxidation) through the hydrogen bond (Fig. 1a). As a result, the OL shows effective afterglow emission. More interestingly, driven by this discovery, an automatic production line was built to convert the natural structural material wood into RTP wood through in-situ oxidation of lignin naturally generated in the wood cell wall (Fig. 1b). Prepared RTP wood shows great potential in building afterglow sustainable furniture.
Figure 1 Schematic diagram of lignin oxidation RTP.
Figure 2 Afterglow RTP emission of OL.
Figure 3 Afterglow RTP mechanism of OL.
Figure 4 Preparation of RTP wood.
In summary, the researchers successfully converted lignin into a sustainable afterglow OL with a lifespan of about 408 ms.What’s more interesting is that driven by this discovery, an automatic production line was built to use natural lignin located in the wood cell wall to generate OL, converting natural wood into RTP wood. RTP wood was then successfully processed into Afterglow Furniture. This work not only demonstrates the sustainability of afterglow RTP materials, but also provides new afterglow RTP structural materials. From a broader perspective, this RTP wood has great potential in wood construction and light management equipment, given the sustainability and ease of processability of natural wood. (Text: Aquatic)
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