2:1 multiplexing function in a simple molecular system

Differential response for multiple ions: a smart probe to construct optically tunable molecular logic systems

A rhodamine-based optical probe has been designed through a one-pot synthetic protocol involving phenanthroline as a binding motif. The compound showed a bright pink coloration specifically upon the addition of Cu²⁺ and Hg²⁺ ions. However, the appearance of bright red fluorescence was observed only in the presence of Hg²⁺. Considering both, we can detect and discriminate these two ions even at ppb level concentration. Furthermore, these in situ generated metal complexes were utilized for the selective recognition of CN^- and I^- ions. Pre-coated TLC plates were developed for rapid on-site detection of these toxic ions even in remote places. Finally, on a single molecular probe based on differential opto-chemical interactions with different ions (Cu²⁺, Hg²⁺, CN^- and I^-), we were able to design numerous trivial (OR, NOR) and non-trivial (INHIBIT, IMPLICATION, COMPLEMENT, TRANSFER, NOT-TRANSFER) logic gates. Most fascinatingly, we can switch the logic response from one type to another by simply tuning only the optical output channel.

Light and Cation-Driven Optical Switch based on a Stilbene-Appended Terpyridine System for the Design of Molecular-Scale Logic Devices

A molecular system comprising a terpyridine moiety capable of coordinating with different cations and a photoswitchable stilbene unit has been utilized here for the fabrication of multiply configurable logic systems. Incorporation of a substituted stilbene unit into the terpyridine motif generates an intraligand charge-transfer-sensitive module whose absorption and emission spectral properties are highly sensitive to light as well as cations. On the basis of the optical response profile of the receptor in the presence of selected cations as well as light of a specific wavelength, we are able to demonstrate multiple Boolean logic functions such as INHIBIT, IMPLICATION, OR, NOR, and NAND, as well as various combinations of them. Of particular interest, we utilized the present system for the construction of security keypad locks and memory devices by maintaining a proper sequence of the stimuli and monitoring either absorption or emission spectral response at a specific wavelength as the output signal. In addition to various Boolean logic functions, the present system has also the ability to mimic fuzzy logic operations for generating an infinite-valued logic scheme depending on its emission spectral responses upon varying the concentration of cationic (Fe²⁺ and/or Zn²⁺) and anionic (CN^-) inputs.