Distinguishing different isomers of the photochromic CMTE molecule on the si(100) surface studied by STM

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 x 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.