Optimizing Excited-State Energies and Electron Transfer Dynamics in Benzothiadiazole-Based Organic Photocatalysts for Improved Efficiency

Organic photocatalysts play a pivotal role in advancing green and sustainable chemistry by enabling efficient and selective photochemical transformations and reducing the need for traditional hazardous reagents and energy-intensive processes. This work uses the donor-acceptor natures, steric effects, and conjugation lengths of six benzothiadiazole (BTD) based organic dyes (PC1-PC6) to control their charge transfer (CT) and locally excited (LE) states. Thus, effective photosensitization and photoredox characteristics are brought about for photocatalytic applications. Additionally, theoretical research shows that the carbazole-linked-BTD with methyl (PC2 and PC3) demonstrates an effective CT feature in the T1 state. While the LE nature of the methyl-free carbazole-linked-BTD dye (PC1) is excellent. TPA-linked-BTD dyes (PC4-PC5), on the other hand, have good LE properties in the T1 state except for mono-TPA-linked-BTD derivative (PC6). For S1 state features, though, the tendency was in the reverse direction. In the S1 state, all the compounds (PC1-PC4) exhibit outstanding HLCT capabilities except the methylated BTD dyes that contain triphenylamine donors (PC5-PC6). The letter compounds possess CT nature in the S1 state. Overall, the donor’s strength and steric effect of the methyl group were found to tune the nature of S1 and T1 states of these photocatalysts with both photosensitization and photoredox qualities. Thus, A universal technique for screening BTD-based dyes has been developed, guided by theoretical insights and confirmed through practical validation. It demonstrates exceptional photocatalytic performance, outperforming traditional benchmark photocatalysts, and holds significant promise for advancing the field. With a wide spectrum of functional group tolerance, the catalysts can selectively oxidize both primary and secondary amine derivatives.