Computational Study of Cresyl Violet Covalently Attached to the Silane Coupling Agents: Application to TiO2-Based Photocatalysts and Dye-Sensitized Solar Cells

Abstract

The covalent attachment of photosensitizing dyes to TiO2 using silane coupling agents (SCAs) is a promising strategy for enhancing the photocatalytic activity of TiO2-based photocatalysts and the photovoltaic conversion of dye-sensitized solar cells (DSSCs). This approach can control the geometry and orientation of the photosensitizing dye on the TiO2 surface. In this study, a density functional theory (DFT) and time-dependent DFT (TD-DFT) investigation was carried out on cresyl violet (CV) covalently attached to SCAs with a terminal oxirane group (OTES–Cn) to reveal the influence of OTES–Cn on the geometry of the photosensitizing dyes. The potential of CV covalently attached to OTES–Cn (CV–OTES–Cn) to act as a photosensitizing dye was also analyzed. The hydroxyl group formed by the epoxy-opening reaction between CV and OTES–Cn strongly influenced the geometry of CV–OTES–Cn, which was attributed to a CH–O interaction. Additionally, TD-DFT, frontier molecular orbital and molecular electrostatic potential calculations revealed that CV–OTES–Cn has excellent optical properties and electron injection ability. In particular, the characteristics of the unbent conformation of CV–OTES–Cn are expected to contribute significantly to the photocurrent in TiO2-based photocatalysts and DSSCs. These findings enhance the understanding of the covalent attachment strategy using SCAs and contribute to improving TiO2-based photocatalysts and DSSCs.

DFT and TD‐DFT Study on Azobenzene‐Based Dye Covalently Attached to Silane Coupling Agents: Toward Dye‐Sensitized TiO2 Catalyst and Dye‐Sensitized Solar Cell Applications

“…However, note that the CB level of Ti 6 O 15 H 6 obtained by the FMO calculations using CPCM in EtOH is À 2.72 eV. [5] MEPs of isolated MPDNA-OTES and MPDNA-OTES adsorbed on the TiO 2 cluster were evaluated to verify the abovementioned results (Figure S10). [7a] In the case of isolated MPDNA-OTES, the highest nucleophilic reaction sites are located in the diazenyl moiety, and the hydrogen atoms of the hydroxyl group and secondary amine moieties demonstrate electrophilic potential.…”

“…As reported in a previous study, the CHÀ O interaction and the steric hindrance caused by the 1-naphthylamine moiety result in two conformers with different torsion and dihedral angles for the secondary amine moieties (CÀ CÀ NÀ C dihedral angle, Figure 4). [5] In the case of E-MPDNA-OTES, the CÀ CÀ NÀ C dihedral angles of the conformers A1 and A2 were evaluated to be 154.2 and 99.6°, respectively. The considerable distortion of conformer A1 was clearly because of the CHÀ O interaction and the steric hindrance of the 1-naphthylamine moiety, which was supported by the energy difference ΔE (based on the sum of the electronic and thermal energies) of 9.8 kJ/mol obtained via the frequency analysis.…”

“…Herein, cluster-sized TiO 2 (namely, Ti 6 O 15 H 6 (anatase TiO 2 (101) surface model)) was employed because of its low computational cost and relatively high computational accuracy and optimized at the B3LYP/6-31G*/LanL2DZ level of theory. [5] SCAs can adsorb on metal oxides in monodentate, bidentate, tridentate, and ladder-like binding modes. [17] The calculated monodentate, bidentate, and tridentate binding models of OTES adsorbed on the TiO 2 cluster was shown in Figure S6.…”

“…J sc is also affected by the regeneration efficiency of the oxidized dye (η reg ). The driving force of dye regeneration (~G reg ) plays a role in the determination of η reg and is expressed by the following equation: [14,19] DG reg ¼ E redox À E dye , (5) where E redox denotes the redox potential of I À /I 3 À (À 4.8 eV) in an electrolyte solution. [7a,12,15] For E-MPDNA-OTES,~G reg of A2 was lower than that of A1.…”

“…[4] Recently, our group has focused on silane coupling agents (SCAs) and reported density functional theory (DFT) and timedependent DFT (TD-DFT) studies of cresyl violet (CV) covalently attached to a series of SCAs (such as 4-(triethoxysilyl)butane-1,2-epoxide (OTES), Figure S1) with a terminal oxirane group, and CV covalently attached to OTES is abbreviated as CV-OTES. [5] Organic dyes are covalently attached to SCAs because of the following reasons: (i) SCAs serve as anchors for the formation of a covalent bond between TiO 2 and organic dyes and (ii) they form self-assembled monolayers (SAMs), which can be attributed to the generation of a siloxane network. [6] The aligned orientation of SAMs based on SCAs can potentially control the geometry and orientation of a dye adsorbed on the TiO 2 surface.…”