Abstract
Charge transport by tunnelling is one of the most ubiquitous elementary processes in nature. Small structural changes in a molecular junction can lead to significant difference in the single-molecule electronic properties, offering a tremendous opportunity to examine a reaction on the single-molecule scale by monitoring the conductance changes. Here, we explore the potential of the single-molecule break junction technique in the detection of photo-thermal reaction processes of a photochromic dihydroazulene/vinylheptafulvene system. Statistical analysis of the break junction experiments provides a quantitative approach for probing the reaction kinetics and reversibility, including the occurrence of isomerization during the reaction. The product ratios observed when switching the system in the junction does not follow those observed in solution studies (both experiment and theory), suggesting that the junction environment was perturbing the process significantly. This study opens the possibility of using nano-structured environments like molecular junctions to tailor product ratios in chemical reactions.
Highlights
Charge transport by tunnelling is one of the most ubiquitous elementary processes in nature
The break-junction techniques could provide a means to statistically quantify the photo-reaction kinetics of a single-molecule device connected between two electrodes, which may offer some new understanding beyond measuring an ensemble of molecules as in other spectroscopies
Benefiting from the well-distinguished conductance states, the reaction kinetics and reversibility could be studied via statistical analysis of the conductance–distance traces, and it is found that the reaction in the junction does not follow those observed in solution, which agrees well with the energy calculation
Summary
Charge transport by tunnelling is one of the most ubiquitous elementary processes in nature. We explore the potential of the single-molecule break junction technique in the detection of photo-thermal reaction processes of a photochromic dihydroazulene/vinylheptafulvene system. The switching of photochromic molecules is accompanied by changes in electronic, structural and/or chemical properties, making photoswitches versatile building blocks for potential applications in materials science, electronics and biotechnology[1,2,3]. Progress in this area requires detailed understanding of these molecules and various analytical techniques have been used to analyse the photoreaction process, such as ultraviolet–visible (UV–Vis) spectroscopy, fluorescence spectroscopy[4,5] and Raman spectroscopy[6,7]. Density functional transport calculations reproduce the relative conductance of these molecular states and identify a changing destructive interference effect as being responsible for the large span in conductance
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