14818
J. Phys. Chem. C 2007, 111, 14818-14822
Distinguishing Different Isomers of the Photochromic CMTE Molecule on the Si(100) Surface Studied by STM A. Bellec, M. Cranney, Y. Chalopin, A.J. Mayne,* G. Comtet, and G. Dujardin Laboratoire de Photophysique Mole´ culaire, CNRS, Bat. 210, UniV Paris Sud, 91405 Orsay, France ReceiVed: May 24, 2007; In Final Form: July 27, 2007
The adsorption of the cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (CMTE) molecule on the clean Si(100)-2 × 1 surface was studied using scanning tunneling microscopy at room temperature. These molecules belong to the class of photochromic dye molecules that undergo reversible photoisomerization between the open and closed isomers when irradiated with light. This is the first observation of individual photochromic molecules on a surface where it is possible to identify the two photoisomers. By changing the ambient lighting conditions prior to deposition, the relative proportion of the two forms of molecules observed on the silicon surface can be changed. The deduction is that the triangular form corresponds to the closed isomer, and the three-lobed form corresponds to the open isomer.
1. Introduction Photochromic dye molecules undergo reversible photoisomerization when irradiated with light.1 Such functionalized molecules could have potential applications in molecular electronics for building molecular size memories or switches.2-4 Photochromic behavior was first observed in azo compounds,5 and more recently, a number of different classes of molecules have beensynthesizedthatshowaphotochromiceffect: diarylethenes,6-8 spiropyran molecules,9 and fulgides.10-11 Indeed, a recent study has shown that the mechanical properties of crystals of diarylethenes are reversibly modified by the photoisomerization, such that the crystals can be used to move attached nanoobjects.12 Irreversible switching has been observed in breakjunction experiments of a fluorinated diarylethene on gold. One of the reaction directions is quenched because of the presence of the gold surface.13 The cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (CMTE) molecule belongs to the family of diarylethenes, and its photoisomerization behavior has been studied in solution and in the solid phase.14-15 The CMTE molecule in its open isomer possesses three adjacent double bonds that permit a ultraviolet-photon induced (
