Lignin-Assisted Photoreactions: Unveiling New Frontiers in Light-Induced Chemistry

Lignin, the most abundant aromatic biopolymer, is emerging as a mainstay of the upcoming revolution in sustainable materials processing. Despite the inherent challenges associated with the heterogeneous structure of lignin, significant progress has recently been made in developing innovative strategies to valorize this fascinating aromatic biopolymer to deliver industry-demanded products via photoreactions. The purpose of this review is to unravel insights into these creative approaches in lignin-assisted photoreactions, focusing on photopolymerization to construct functional polymeric materials and photoreduction to provide valuable chemicals, wherein lignin serves as a macromolecular photoinitiator and a reductive photocatalyst, respectively. The existing strategies for improving the photochemical quantum yield of lignin in photopolymerization and harnessing lignin macromolecules as photoresponsive polymers to facilitate electron transfer in photocatalytic reactions are also summarized. In the future, such photochemical lignin valorization concepts could potentially provide new possibilities for achieving a profitable value chain for integrated biorefinery processes.