We report a theoretical study of single molecule conduction in open and closed conformations of photochromic dithienylethene molecules attached to metallic
leads. Photochromic molecules are attractive candidates for use in molecular electronics because of the switching between different states with different conducting behaviour. This opens the possibillity for optically controlled conduction.
Dithienylethene derivatives in solution transforms under UV irradiation from the open to the closed comformation, while the reverse process occurs under visible light. When attached to gold leads, however, the ring closure reaction
appears to be quenched, thus destroying the reversible switching mechanism. One theory as to why this happens is that the quenching arises from charge transfer from the molecular HOMO to the leads, due to strong coupling to the gold d-states, which lie close to the Fermi level.
We have therefore investigated the alignment of the molecular levels to the lead orbital-resolved density of states for gold and silver under finite bias for ring opening and closing reactions. We find that the HOMO
level coupling to the lead d-states is significantly weaker for the silver lead system. Therefore, provided the quenching has the electronic origin mentioned above, we predict the reaction to become reversible if the gold
leads are replaced by silver leads.
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