Photochromic Switches Incorporated in Bridging Ligands: A New Tool to Modulate Energy-Transfer Processes

The thoughful construction of molecular switches has led to a gamut of supramolecular systems that can be used in molecular electronics. These include molecules based on thienylethenes, spiropyrans, fulgides, dithienylphenanthrolines, and diazafluorenes. This article reviews the recent developments made in the synthesis and characterization of all these systems, thereby allowing a comparative study to validate the viability of these switchable molecules on a nanoscale. Also, the drawbacks of each class are demonstrated and, at the same time, the remedies for further improvisation are prescribed. We have made an honest attempt to present an exhaustive account of all the different photochromic switches developed by us hitherto. New photochromic bridging ligands with covalently bound 2,2′‐bipyridine or phenanthroline coordinating moieties have been prepared. The bridging ligand, with a dithienylethene switching moiety, shows remarkable energy‐transfer properties from the donor to the acceptor unit (see Figure). The open form induces an efficient energy transfer, while the switching unit in the closed form acts as a trap for the same process.