This thesis reports new methods using both reductive and oxidative quenching cycles in photoredox catalysis for organic synthesis aiming at the synthesis of quinoline and ullazine derivatives, the synthesis of aryl thiols and the oxidation of lignin model compounds. In Chapter 1, we have compared reported approaches of transition metal catalyzed and photoredox catalyzed valorization of lignin subunits and discussed the advantages and disadvantages of the methods. We have also discussed the results of our photocatalytic approach on the oxidation of lignin model compounds. In Chapter 2, we have developed a novel method for the synthesis of quinoline and ullazine derivatives. The organic dye Rhodamine 6G (Rh-6G) can undergo a consecutive pho...