Molecules with multiple light-emissive electronic excited states as a strategy toward molecular reversible logic gates

A variety of molecule-based logic gates have been developed where chemical and/or physical inputs promote molecular changes integrating up to two logic gates and focusing on Boolean interpretations derived from irreversible gates. However, reversible logic has its uses in quantum computing, low-power CMOS, and optical and DNA computing. In this paper, we demonstrate the integration of three logic gates (viz., an XOR gate and two complementary INHIBIT gates) in a single molecule as a strategy toward developing molecules that can operate in a reversible logic mode by exploiting the four light-emissive electronic excited states. The fluorescence emission from two homologous but inherently different charge-transfer states can be applied toward a conservative XOR gate in such a way that the 11 and 10 outputs can be used to derive the 01 and 10 inputs. This provides an alternative to existing molecular irreversible logic gates, an approach that has raised an enormous expectation, but which contain less information in their output than is present in their inputs. In a complementary way, a half-subtractor based on a combination of the XOR gate and one of the INHIBIT gates was thus produced.