We report the in situ observation of photochemical reactions on individual nano objects of solid catalysts using single-molecule, -particle fluorescence spectroscopy. The use of high-resolution imaging techniques with suitable fluorogenic probes enables us to determine the location of the catalytically active sites that are related to the structural heterogeneities on the surface of the solid catalyst and the temporal fluctuation of photochemical reactivity. Recent developments of single molecule spectroscopy will extend the range of applications by adding new tools. Advanced �nanoscopy� techniques such as two or three-dimensional stimulated emission depletion microscopy and photoactivated localization microscopy/stochastic optical reconstruction microscopy have achieved optical imaging at high spatial resolution beyond the optical diffraction limit (around half the wavelength of the light in the lateral direction). This feature should be highly advantageous and useful in exploring the active sites heterogeneously distributed over the materials. However, it should be noted that the localization accuracy might be less than that expected from a certain S/N ratio due to �distorted� field distributions of the emitter in the vicinity of metal nanostructures. Another important aspect is that molecular adsorption/ desorption kinetics are strongly associated with the surface structures of the catalysts. The molecular recognition and transformation on specific surfaces should play a crucial role in controlling reaction efficiency and selectivity. The combination of fluorescence microscopy with several microscopic techniques such as TEM, SEM, AFM, Raman microscopy, and optical absorption microscopy will become extremely powerful approaches to gain structural and dynamic information on broad spatial and temporal ranges. We believe that single-molecule, -particle approaches will serve as the basis for designing and identifying new materials for applications in a variety of areas including biomedicine, catalysis, and optoelectronics.

Single-molecule, single-particle approaches for exploring the structure and kinetics of nanocatalysts

247th National Meeting (2014)

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