Stéphane Rigaut, Corinne Lagrost, Karine Costuas and colleagues from CNRS-University of Rennes have prepared a photo/electrochromic multifunctional switching system, based on Irie's dithienylethene photochromic unit ([Cl(dppe)₂Ru]⁺ where dppe = 1,2-bis(diphenylphosphino)ethane). The switch is reversible, and a change of structure (corresponding to different physical properties) can be triggered both by light and by altering electric potential. 

Rigaut explains that metallic systems are 'excellent candidates' for developing multifunctional switches 'because they give rise to electrochromism with strong optical contrast, high coloration and low switching potential. Also they can lead to the establishment of synergetic properties when associated with specific organic systems.'

The organometallic ruthenium unit promotes a strong electronic coupling between the metal centers and the conjugated organic ligands. This leads to a molecular switch with multicolor electrochromism, electrocyclization at a remarkably low voltage, and photo/electro control of electronic communication within a molecular wire. 

Rigaut predicts that understanding and controlling the interactions between molecules when grafted onto a surface will be crucial for the creation of molecular devices. A second crucial factor, adds Rigaut, will be understanding and control of the connections between these molecular components and the macroscopic metal components which transmit information to the more traditional electronic components. 

Rachel Cooper