Electronic Coupling–Decoupling-Dependent Single-Molecule Interfacial Electron Transfer Dynamics in Electrostatically Attached Porphyrin on TiO2 Nanoparticles

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• 作者：Bharat Dhital ; Vishal Govind Rao ; H. Peter Lu
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 9, 2016
• 年：2016
• 卷：120
• 期：22
• 页码：12313-12324
• 全文大小：710K
• 年卷期：0
• ISSN：1932-7455

文摘

Factors controlling the interfacial electron-transfer (ET) dynamics in molecule–semiconductor systems have been intensively investigated in recent years. Here, we study dynamics of interfacial ET on Zn(II) meso-tetra (N-methyl-4-pyridyl) porphine tetrachloride (ZnTMPyP)–TiO₂ nanoparticle (NP) system using single-molecule photon-stamping spectroscopy while electrostatically controlling the coupling between ZnTMPyP and TiO₂ NP by changing the surface charge of the TiO₂ NP. The single-molecule fluorescence trajectories show strong fluctuation and blinking between bright and dark states providing clear indication for the binding affinity between ZnTMPyP and the TiO₂ NP via electrostatic interaction. By changing the surface charge on the TiO₂ NP, positive or negative, we are able to change the coupling between ZnTMPyP and the TiO₂ NP, which is revealed from the dominant dark states distribution in fluorescence trajectories and shorter fluorescence lifetime of ZnTMPyP attached on negatively charged TiO₂ NP surface compared to positively charged TiO₂ NP surface. The observed difference in fluorescence trajectories and lifetime of ZnTMPyP can be qualitatively accounted for by considering the change in purely electronic coupling factor caused by the positively or negatively charged TiO₂ NP surface in electrostatically bound dye-sensitized TiO₂ systems. Strong binding interaction between ZnTMPyP and negatively charged TiO₂ NP is further observed by higher fluorescence anisotropy compared to ZnTMPyP on positively charged TiO₂ NP.