In this project, we will explore quantum chemical calculations (density functional theory) together with photoredox catalysis and organic photochemistry to elucidate reaction mechanism during lignin depolymerization. We will calculate ground and excited state redox potentials of photoredox catalysts and substrates to control the reactivity and selectivity. Ground and excited state potential energy surfaces passing through various transition states and reaction pathways will also be investigated. Lignin is a heterogeneous aromatic biopolymer which is present in plant cell walls along with cellulose and hemicelluloses. There is a need to find mild, efficient and cost-effective ways to produce biofuel and commodity chemicals from lignin. Variety of delignification methods, i.e., physical, chemical, and biological are already known. Now a days, photoredox catalysis is becoming a powerful activation mode for the development of new strategies in chemical synthesis. This project in particular will focus on aryl-aryl bond breaking in the bonding linkage 5-5 which is much less explored. Therefore, computational methods together with photoredox catalysis will be very useful to design new efficient methods for delignification.