PHOTORESPONSIVE COMPONENTS FOR USE AS VARIABLE RESISTORS FOR APPLICATIONS IN MOLECULAR-SCALE ELECTRONICS

Molecular electronics, an emerging interdisciplinary field spanning physics, chemistry, and materials science, holds promise for extending Moore's law beyond the anticipated limits of conventional silicon-based electrical circuits. A major theme within the field concerns the design and fabrication of simple molecules able to duplicate the essential features of macroscopic electronic components, both passive (e.g., conducting wires) and active (e.g., capacitors). Here, we propose to integrate a photo-responsive switch into a molecular-scale circuit in such a way that the switch can be opened by illumination with a laser pulse. As with a normal switch, the electronic properties will change dramatically once opened and this situation will be tested in several logical circuits. Whilst opening of the switch is very fast, subsequent closure will be slow and can be followed in real time. This situation will permit the electronic properties to be monitored during closure. The operating principle involves restricted rotation around a carbon-carbon bond and the switch will be adapated to stabilise a charge-separated state formed under visible light illumination. Thus, the bridge in a donor-bridge-acceptor molecule will be optimised for fast through-bond electron transfer when the donor absorbs a photon. A second pulse, delivered at a different frequency, will open the switch and convert the bridge to a poor conductor. Charge recombination will be slow, because of the unfavourable conformation, and the charge-separated state will be available for chemical applications.