The Ultrafast Temporal and Spectral Characterization of Electron Injection from Perylene Derivatives into ZnO and TiO₂ Colloidal Films

Abstract

The ultrafast injection dynamics, early recombination dynamics, and spectral signatures of four systematically varied dye-metal oxide hybrid systems were investigated using transient absorption spectroscopy techniques. First, photoinduced electron transfer from two different perylene derivatives into zinc oxide (ZnO) colloidal films is reported. Here, the electronic coupling of the perylene chromophore 2,5-Di-tert-butyl-perylene-9-yl-propionic acid (1) to the ZnO colloids was weaker than the electronic coupling of the chromophore 2,5-Di-tert-butyl-perylene-9-yl-acrylic acid (2). Second, the photoinduced electron transfer of the same two molecules attached to TiO2 colloids was measured and compared to the results for the ZnO colloids using the same techniques. The temporal traces at both the excited-state and the cationic state of the chromophores attached to the semiconductor surfaces were measured simultaneously and showed very good agreement, which indicated a direct injection into the semiconductor. The overall injection times for the ZnO samples was as short as 190 fs, which suggested a strong electronic coupling element for these systems. This injection time is short compared to reports on similar ZnO hybrid systems, but it is still longer than the injection times reported for the TiO2 hybrid systems. The transient absorption spectra of molecule 2 attached to TiO2 showed a large negative signal at 530–550 nm, which indicated the presence of a direct charge transfer state contribution in this system.

A surface science perspective on TiO2 photocatalysis

“…In most cases, modification of the optical properties of TiO 2 results simply from inclusion of the optical transitions of the surface modifier; however, in other cases the electronic states of TiO 2 can be affected by the modifier. For example, when the TiO 2 surface is decorated with: UV/vis-active oxides (such as WO 3 [141][142][143][144], SnO 2 [145], and Fe 2 O 3 [146] among many), metal clusters (such as Ag [147][148][149][150][151][152], Au [153][154][155][156][157] or Pt [154,[158][159][160][161][162]) possessing visible light active plasmonic transitions, or certain molecules (such as sensitizing dyes [163][164][165][166], stearic acid [167] or chlorophenols [168][169][170][171][172]) in which charge transfer (CT) states are generated from adsorption. The case of chlorophenols provides an example of how the absorptive properties of TiO 2 surfaces can be modified by molecular adsorption.…”

Photoinduced electron transfer processes in dye-semiconductor systems with different spacer groups

“…These systems allow a direct comparison with results from ultrafast laser spectroscopy experiments. 4,23,62,[77][78][79] Photoinduced ET in these systems has also been studied in great detail theoretically employing a semiempirical model, 50,53,59,80 thus allowing a comparison with results of our first-principles-based simulations.…”

Titanium Dioxide in Photocatalysis

“…The surface additives may be either organic such as dyes [137] and surfactants [138] or inorganic such as metallic ions and clusters [139,140] or metal oxides [141]. For bulk doping of TiO 2 , the most studied route is an n-type self-doping associated to the presence of Ti 3+ ions in the lattice.…”