Evaluation of darrow red-organosilane composite as a photosensitizer for application in dye-sensitized zinc oxide photocatalysts: DFT and TD-DFT studies.

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Density functional theory (DFT) and time-dependent DFT (TD-DFT) studies of darrow red covalently attached to 3-glycidyloxypropyltrimethoxysilane (DR-GPTMS) were conducted, and it was shown that DR-GPTMS can be applied as a photosensitizer in dye-sensitized zinc oxide (ZnO) photocatalysts. The frontier molecular orbital (FMO) levels of DR-GPTMS simulated using a conductor-like polarizable continuum model in water were suitable for electron injection from photoexcited DR-GPTMS to ZnO. Additionally, the oxidized DR-GPTMS produced by electron injection can be regenerated using triethanolamine. UV-visible absorption spectra, FMOs, and density of states spectra of DR-GPTMS adsorbed on the Zn2O3 cluster were also investigated to understand the mechanism of electron injection. The results suggest that DR-GPTMS induces good visible-light absorption and efficient electron injection to ZnO. DFT and TD-DFT calculations were performed using the Gaussian 09W package (Gaussian, Inc., Wallingford, CT, USA). The density of states spectra was obtained using GaussSum (3.0.2). The B3LYP/6-31G** level of theory was employed for all calculations except for the UV-visible absorption spectra simulation. In calculations involving ZnO, the LanL2DZ or SDD basis set was assigned to the zinc atoms. TD-DFT calculations were performed at the eight different functionals (B3LYP, PBE0, M06-L, M06, M06-2X, M06-HF, CAM-B3LYP, and ωB97XD) with the 6-31+G** basis set. A conductor-like polarizable continuum model (CPCM) using water was employed determining the solvent effect.