Conformational and Binding Effects on Interfacial Electron Transfer from Dual-Linker Sensitizers

Abstract

Interfacial electron transfer (IET) between novel dual-linker perylenes and TiO 2 was investigated by ultrafast spectroscopy and nonadiabatic quantum mechanics/molecular mechanics (QM/MM) simulations. The influence of the number of linkers (one vs two) and their substitution position (ortho vs peri) on IET was investigated. Perylene sensitizers derivatized with two acrylic acid linkers in the peri position, pDtBuPe-(C 2 H 2 COOH) 2 (bis-peri), and in the ortho position, oDtBuPe-(C 2 H 2 COOH) 2 (bis-ortho), were compared to their single-linker counterparts: pDtBuPeC 2 H 2 COOH (peri) and oDtBu-PeC 2 H 2 COOH (ortho). MM simulations of the bis-peri and bisortho sensitizers predicted that, in both cases, only one linker binds covalently to the {101} surface of anatase TiO 2 , while the second one binds weakly via vdW or hydrogen-bonding interactions. Results from QM/MM simulations corroborated experimental injection times for all compounds, thereby supporting single-linker binding to the surface for the dual-linker sensitizers. The study showed that, surprisingly, IET from bis-peri was significantly slower than that from peri. Theory attributes this behavior to small conformational changes caused by steric interactions. The degrees of freedom that are most strongly correlated with variations in IET times were identified by principal component analysis. Comparison between bis-ortho and ortho showed, as expected, that the dual-linker sensitizer injects faster than the single-linker variant. However, the influence of the substitution position on IET was much smaller than expected based on the difference in the static electronic structure. Finally, the strong effect of conformational changes on IET was also observed experimentally in modulations of IET due to coupling to vibrational modes, in excellent agreement with the QM/MM simulations. This study shows that small conformational changes and vibrational coupling can have a significant influence on IET even on the femtosecond time scale. The addition of linkers that differ in bonding strength and serve different functions opens up new avenues for controlling IET dynamics.

Morphology, Energy Level Alignment, and Charge Transfer at the Protoporphyrin IX–Semiconductor Interface

“…The strong excitation wavelength dependence for GaN indicates that the electron transfer from the S2 state to the substrate occurs at a time scale that is at least as fast as the thermalization time needed for relaxation from S2 to S1, which is determined to be on the order of a few femtoseconds by Marcelli et al for PPIX in solution. While charge transfer processes on the order of a few tens to hundreds of femtoseconds are regularly observed, ,− it is not certain what the specific time scale would be for the investigated systems. Additionally, the time scale for relaxation could be extended by the influence of surrounding molecules influencing the vibrational properties of the PPIX.…”

In Silico Optimization of Charge Separating Dyes for Solar Energy Conversion

“…GFN‐xTB has been optimized for a proper description of molecular geometries and frequencies and has proven reliable in a wide variety of systems [19] . The quantum propagation method has also been applied to describe the photoinduced electron injection in dye‐sensitized photoanodes [3,4b,18a,20] …”