Single-molecule chemistry

Single molecule chemistry induced by an STM is one of the new frontiers in surface chemistry, and it is beyond the scope of this chapter to treat this in any meaningful way. Only a brief discussion of one system is given to illustrate the relationship to many of the dynamic principles discussed here. The reader is referred to an excellent review article for recent status in this field [417]. 

As discussed in Section 4.4.1, 02 molecularly adsorbs onto Pt(lll) into two molec-ularly adsorbed states an 02 state centered at the bridge site and an 02 state centered at the fee hollow site. When an STM tip is positioned over an isolated 02 adsorbate, tunneling electrons from the tip induce dissociation of only that molecule without affecting the surrounding [153,326]. The instant of dissociation is readily 

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Pascual JI, Lorente N, Song Z, Conrad H, Rust HP (2003) Selectivity in vibrationally mediated single-molecule chemistry. Nature 423 525... 

Figure 3.1. Schematic of bond making/breaking process considered in this chapter (a) atomic adsorption/desorption/scattering, (b) molecular adsorption/desorption/scattering, (c) direct dissocia-tion/associative desorption, (d) precursor-mediated dissociation/associative desorption, (e) Langmuir-Hinschelwood chemistry, (f) Eley-Rideal chemistry, (g) photochemistry/femtochemistry, and (h) single molecule chemistry. Solid figures generally represent typical intial states of chemistry and dashed figures the final states of the chemistry.

While the importance of the breakdown of the BOA in thermal chemistry is still controversial, the time-reversed process of creating chemistry from hot electrons is well established. Because experiments are generally performed under conditions where there is no adiabatic chemistry, hot electron induced chemistry is easily identified and studied, even when the cross-section for the chemistry is very small. Typical scenarios involve photochemistry, femtochemistry and single molecule chemistry on surfaces. A few well-studied examples are discussed briefly in Section 4.8. Because a detailed discussion of these active fields would take this chapter far from its original purpose, they are only treated briefly to illustrate the relationship to other aspects of bond making/breaking at surfaces. 

Keywords Vibrational spectroscopy scanning tunneling microscopy and spectroscopy conductance inelastic conductance single-molecule chemistry controlled manipulation mode-selective reactivity. 

In this chapter, we review important concepts regarding vibrational spectroscopy with the STM. First, the basis of the technique will be introduced, together with some of the most relevant results produced up to date. It will be followed by a short description of experimental issues. The third section introduces theoretical approaches employed to simulate the vibrational excitation and detection processes. The theory provides a molecular-scale view of excitation processes, and can foresee the role of various parameters such as molecular symmetry, adsorption properties, or electronic structure of the adsorbate. Finally, we will describe current approaches to understand quenching dynamics via internal molecular pathways, leading to several kinds of molecular evolution. This has been named single-molecule chemistry. 

The few experiments available to date about single-molecule chemistry have provided a different view of understanding the complexities behind excitation and relaxation of vibrational in adsorbates. Certainly, more than a tool for technological processing, it will develop concepts and strategies for selectively studying catalytic reactions. 

Part V focuses on single molecule chemistry at metal surfaces. Herein the chapter by S. W. Hla and K. Braun describes how the STM can be used to induce single molecule reactions, starting from bond breaking all the way to bond formation. The chapter by N. Lorente deals with atomic scale vibrational spectroscopy studies and how they allow to obtain chemical information on individual molecules. 

Antonietti, M. and Landfester, K. (2001) Single molecule chemistry with polymers and colloids a way to handle complex reactions and physical processes Chem. Phys. Chem. 2(4), 207-10. 

Moemer WE (2007) Single-molecule chemistry and biology special feature new directions in single-molecule imaging and analysis. Proc Natl Acad Sci USA 104 12596-12602... 

Silbey, R. J., Single molecule Chemistry and Biology. Special Feature, Proc. Natl. Acad. Sci. 2007, 104, 12596 12602. 

The chapter starts with the synthesis aspects of dendronized polymer research, with details of the three synthetic pathways, assisted by reported examples that help to distinguish the difierent synthetic strategies in terms of their efficiency and fidehty towards generating dendronized polymers of respectable thickness and length. The responsivity of the dendronized polymers - which is an important feature of this unique class of polymers, and may lead to some interesting apphca-tions - is then discussed, followed by details of the single-molecule chemistry and use of dendronized polymers as building blocks for nanoconstruction purposes. 

Li ZY, Li B, Yang JL, Hou JG (2010) Single-molecule chemistry of metal phthalocyanine on noble metal surfaces. Acc Chem Res 43 954—962... 

Figure 3.1 Compilation of different chro-mophore families with regard to their utility for single-molecule chemistry, based on Web-of-Science database search. Flu-orophores with excitation in the green to red region of the visible electromagnetic spectrum are superior to blue and...

Single Molecule Chemistry and Physics An Introduction (NanoScience and Technology) by C. Wang (Author) and C. Bai (Author)... 

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