Photoinduced proton exchange between molecular switches

The identification of strategies to establish communication between independent molecules is an essential requirement for the development of operating principles to manipulate information at the molecular level. In this context, we have devised a strategy to exchange signals between pairs of complementary molecular switches. It is based on the photoinduced ring closing of a merocyanine to produce a spiropyran with the concomitant release of a proton. The liberated proton is captured by either one of two pyridine derivatives with the formation of their conjugate acids. This transformation induces a significant increase in chemical shift for the resonances of the pyridyl protons and, in one instance, also a pronounced color change. The overall process is fully reversible and the pair of communicating molecules reverts to the original state in the dark. Relying on this mechanism, an optical input is transduced into a detectable spectroscopic output after the controlled intermolecular exchange of protons. A simple analysis of the signal transduction operated by the communicating molecular switches reveals that a binary digit is passed unaltered from the input to the output even although the nature of the signal carrying the information changes at each step. Furthermore, the different nature of input and output implies that the state of the ensemble of molecules can be probed non-destructively at any point in time. The timescales of the switching steps, however, are seriously limited by the slow reaction kinetics. The photoinduced transformation occurs within minutes, but the thermal reaction reverts the switch state only after several hours.