HOMO-LUMO Energy Levels and the Bandgaps to Understand Porpc Photocatalytic Activity

Abstract

A dye-sensitized solar cell (DSSC) assembly can be used not only to harvest solar energy but also to purify water using suitable dye-sensitizers. Here, we theoretically investigated four dye-sensitizers, namely, PORPC-1, PORPC-2, PORPC-3, and PORPC-4 for photocatalytic water purification using PBE, B3LYP, PBE0 functionals, and ∆SCF, TD-DFT and GW methods to characterize their activity trends. The energy levels of highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) were elucidated using gas-phase and aqueous phase calculations to understand charge injection ability and the dye-regeneration process. However, PBE, B3LYP, PBE0, and TD-DFT methods fail to predict the best sensitizers. The ∆SCF coupled with the implicit solvation method and the GW method HOMO-LUMO energies corrected for aqueous environment effect predicted PORPC-2 and PORPC-4 as the best sensitizers. Thus, it emphasized the importance of aqueous environment effect in simulation. However, none of these methods accurately predicted the photocatalytic performance trend of all the four dye-sensitizers. Hence, we have used the dye-molecular aggregation assembly pattern in an aqueous environment to further probe into activity trends and found that the PORPC-3 and the PORPC-4 prefer J-aggregate assembly, whereas the PROPC-1 and the PORPC-2 adopt H-aggregate assembly pattern. Therefore, the synergistic effect of the HOMO-LUMO energy levels and the aggregate assembly pattern determine the photocatalytic performance of the dye-molecules, and the activity trend is PORPC-4>PORPC-2>PORPC-3>PORPC-1, agreed well with the experimental findings. Acknowledgements This study was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Nos. NRF-2017R1E1A1A01074266, NRF-2015M1A2A2057129, and NRF-2016M1A2A2937151).