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Heterogeneous Electron-Transfer Dynamics through Dipole-Bridge Groups.

ABSTRACT: Heterogeneous electron transfer (HET) between photoexcited molecules and colloidal TiO2 has been investigated for a set of Zn-porphyrin chromophores attached to the semiconductor via linkers that allow to change level alignment by 200 meV by reorientation of the dipole moment. These unique dye molecules have been studied by femtosecond transient absorption spectroscopy in solution and adsorbed on the TiO2 colloidal film in vacuum. In solution energy transfer from the excited chromophore to the dipole group has been identified as a slow relaxation pathway competing with S2-S1 internal conversion. On the film heterogeneous electron transfer occurred in 80 fs, much faster compared to all intramolecular pathways. Despite a difference of 200 meV in level alignment of the excited state with respect to the semiconductor conduction band, identical electron transfer times were measured for different linkers. The measurements are compared to a quantum-mechanical model that accounts for electronic-vibronic coupling and finite band width for the acceptor states. We conclude that HET occurs into a distribution of transition states that differs from regular surface states or bridge mediated states.

SUBMITTER: Nieto-Pescador J

PROVIDER: S-EPMC5418589 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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Heterogeneous Electron-Transfer Dynamics through Dipole-Bridge Groups.

Nieto-Pescador Jesus J Abraham Baxter B Li Jingjing J Batarseh Alberto A Bartynski Robert A RA Galoppini Elena E Gundlach Lars L

The journal of physical chemistry. C, Nanomaterials and interfaces 20151216 1

Heterogeneous electron transfer (HET) between photoexcited molecules and colloidal TiO<sub>2</sub> has been investigated for a set of Zn-porphyrin chromophores attached to the semiconductor via linkers that allow to change level alignment by 200 meV by reorientation of the dipole moment. These unique dye molecules have been studied by femtosecond transient absorption spectroscopy in solution and adsorbed on the TiO<sub>2</sub> colloidal film in vacuum. In solution energy transfer from the excite ...[more]

PMID: 28479939

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Project description:The electrochemical response of different morphologies (microstructures) of vertically aligned graphene (VG) configurations is reported. Electrochemical properties are analysed using the outer-sphere redox probes Ru(NH3)6 2+/3+ (RuHex) and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), with performances de-convoluted via accompanying physicochemical characterisation (Raman, TEM, SEM, AFM and XPS). The VG electrodes are fabricated using an electron cyclotron resonance chemical vapour deposition (ECR-CVD) methodology, creating vertical graphene with a range of differing heights, spacing and edge plane like-sites/defects (supported upon underlying SiO2/Si). We correlate the electrochemical reactivity/response of these novel VG configurations with the level of edge plane sites (%-edge) comprising their structure and calculate corresponding heterogeneous electron transfer (HET) rates, k 0. Taller VG structures with more condensed layer stacking (hence a larger global coverage of exposed edge plane sites) are shown to exhibit improved HET kinetics, supporting the claims that edge plane sites are the predominant source of electron transfer in carbon materials. A measured k 0 eff of ca. 4.00 × 10-3 cm s-1 (corresponding to an exposed surface coverage of active edge plane like-sites/defects (% θ edge) of 1.00%) was evident for the tallest and most closely stacked VG sample, with the inverse case true, where a VG electrode possessing large inter-aligned-graphene spacing and small flake heights exhibited only 0.08% of % θ edge and a k 0 eff value one order of magnitude slower at ca. 3.05 × 10-4 cm s-1. Control experiments are provided with conventional CVD (horizontal) grown graphene and the edge plane of highly ordered pyrolytic graphite (EPPG of HOPG), demonstrating that the novel VG electrodes exhibit ca. 3× faster k 0 than horizontal CVD graphene. EPPG exhibited the fastest HET kinetics, exhibiting ca. 2× larger k 0 than the best VG. These results are of significance to those working in the field of 2D-carbon electrochemistry and materials scientists, providing evidence that the macroscale electrochemical response of carbon-based electrodes is dependent on the edge plane content and showing that a range of structural configurations can be employed for tailored properties and applications.

Dataset Information

Heterogeneous Electron-Transfer Dynamics through Dipole-Bridge Groups.

Publications

Heterogeneous Electron-Transfer Dynamics through Dipole-Bridge Groups.

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