Semiconductor quantum dots (QDs) are intriguing light-harvesters and excited-state charge donors for solar energy conversion, due to their size-dependent optical properties and band-edge potentials, high oscillator strengths, and the possibilities of hot-carrier extraction and multiexciton generation. One strategy to exploit these properties is to tether QDs to electron- or hole-accepting semiconductor substrates via bifunctional molecular ligands. Interfacial charge transfer from photoexcited QDs to the semiconductor can initiate redox chemistry and/or the generation of electrical power. Electron-transfer (ET) reactivity at QD-molecule-semiconductor interfaces depends on the properties of molecular linkers or “bridge” molecules. We have reported on the influence of through-bridge distance and electronic coupling on ET dynamics and yields in dispersed QD-molecule-semiconductor heterostructures.1-3 This poster will present an extension of this effort to explore the influence of the length of linear mercaptoalkanoic acid (MAA) linkers on the dynamics and yield of ET from photoexcited CdSe QDs to TiO2 within nanocrystalline thin films. We hypothesized that, within the mesoporous films, the rate constants of ET may be limited either by through-bridge distance and electronic coupling or by through-space QD/TiO2 interactions. That is, prior results pertaining to interparticle ET within dispersed heterostructures may or may not translate to the thin films that are relevant to QD-sensitized solar cells and photocatalysts. Excited-state deactivation and ET were characterized by transient absorption spectroscopy on time scales of 10-8 to 10-5 s. Excitation of CdSe QDs yielded a transient bleach of the first excitonic absorption band, the intensity and lifetime of which varied substantially with the length of MAA linkers and the properties of the semiconductor substrate, suggesting that interfacial ET yields depend critically on properties of molecular linkers within thin-film architectures. Ongoing transient absorption measurements are expanding the scope of our work to address a range of properties of molecular linkers. Results from these experiments will be presented. 1. Dibbell, R.S.; Watson, D.F. J. Phys. Chem. C 2009, 113, 3139-3149. 2. Dibbell, R.S.; Youker, D.G.; Watson, D.F. J. Phys. Chem. C 2009, 113, 18643-18651. 3. Nevins, J.S.; Coughlin, K.M.; Watson, D.F. ACS Appl. Mater. Interfaces 2011, 3, 4242-4253.

Excited-state electron transfer from CdSe quantum dots to TiO2: Influence of the properties of molecular linkers on electron transfer within mesoporous films

251st National Meeting (2016)

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