Light-powered molecular logic goes nonlinear

A unique way to increase the dimensions of molecular logic schemes is reported in PNAS (1). What is molecular logic? Does it promise the ultimate flexible electronics—a liquid computer? Not exactly, although switchable molecules could be used in logic components, perhaps augmenting traditional electronics (2). The field of molecular logic, however, is much broader than that (3, 4). A good way to appreciate the promise and motivation for molecular logic is to realize how biology uses highly developed chemical switches connected to sophisticated sensors and feedback loops (5). It is a powerful idea that robust information processing can be carried out in complex systems rather than perfectly arranged semiconductor switches. In biological systems, multiple input signals can be processed, and seemingly intelligent choices are expressed as the output. For example, this is seen in the way plants respond to excess sunlight—a process called nonphotochemical quenching that deactivates excited electronic states in light-harvesting complexes when reaction centers are running at capacity (6). Various input signals are used, including pH of the thylakoid lumen. A remarkable range of responses are coordinated: from rerouting electrons to chemically modifying carotenoids to gene regulation (7). These responses are invoked over an expanse of timescales to help protect nature’s solar cells. Biology is a rich ground of inspiration for sensors based on molecular logic. Examples have been reported where, instead of simply detecting the concentration of an analyte, the way the concentration is modulated in time is sensed. Such an instance is the report …