Browsing by Author "Yan, Han"
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Item Interfacial electron transfer of perylenes: Influence of the anchor binding mode(The Journal of Chemical Physics, 2024-01-21) Yan, Han; Harmer, Ryan; Zafar, Binish; Galoppini, Elena; Gundlach, LarsInterfacial electron transfer (IET) through saturated single-linker and dual-linker groups from a perylene chromophore into nanostructured TiO2 films was studied by ultrafast spectroscopy. Perylene chromophores with one and two propanoic acid linker groups in the peri and ortho positions were investigated. In comparison to previously studied perylenes bound via unsaturated acrylic acid linkers, the chromophores with saturated linkers showed bi-exponential IET dynamics. Two distinct transfer times were observed that indicate the presence of two concurrent binding modes. A comparison between ortho- and peri-substituted sensitizers resulted in slower IET dynamics and weaker electronic coupling for ortho substitution. Finally, IET from sensitizers with saturated linker groups is neither promoted nor hindered by a second linker group. This indicates that only one of the two linkers binds covalently to the surface. This study reveals the importance of the anchor-binding mode and design considerations of the linker for regulating IET.Item Photoinduced heterogeneous electron transfer : ǂb spectroscopic investigation on perylene chromophores on TiO2 colloids(University of Delaware, 2023) Yan, HanPhotoinduced heterogeneous electron transfer (HET) is fundamentally important in many physical, chemical, and biological processes, with a wide range of applications such as photocatalysis, sensors, dye-sensitized solar cells, photolithography, and artificial photosynthesis. In photoinduced HET, a photoexcited electron is transferred from a molecular donor state to multiple acceptor states in a semiconductor. These reactions can occur on time scales as short as a couple of femtoseconds. ☐ In this dissertation, HET is studied with ultrafast spectroscopy on HET systems comprised of perylene derivatives that are covalently bound to colloidal TiO2 surfaces. Perylene chromophores have been chosen for their electronic and optical properties, making them ideal model systems. The specific focus of this work involves the manipulation of the conformation and chemical structure of the linker group that attaches the perylene chromophore to the TiO2 surface. Ultrafast spectroscopy was employed to gain insights into dynamics, electronic coupling, vibrational states, and various effects such as vibronic, structural, and binding effects. ☐ Transient absorption and pump-degenerate four-wave mixing were the primary ultrafast spectroscopies used to study HET and the vibrational response of the system. The experimental results were compared with theoretical simulations from collaborators and revealed the importance of electronic-vibrational coupling on HET. Perylene chromophores with systematic changes in the substitution position and number of linker groups were compared, yielding unexpected results that were explained by vibronic effects, binding effects, as well as conformational effects.