NAND molecular logic gate

Figure 5.1 Three compounds that were synthesized for studies in computing using electrostatic potentials. 1 is a molecular three-terminal junction that could be used as a molecular interconnect. 2 is a molecular-sized switch for which there is a corresponding equivalent of a source, drain and gate terminals of a bulk solid state FET. 3 is a can be an active OR or a passive NOR gate if positive logic is used or an AND or NAND gate if negative logic is used. ...

Tanaka and Iwata1561 have described an interesting system (14) that displayed all the hallmarks of a NAND logic gate at the molecular scale. The fluorescence of the heteroaromatic unit is quenched only when Ba2+ and SCN- ions are simultaneously present at suitably high concentrations. The fluorescence-quenching PET process comes into action only when the electron-rich SCN- is held near the fluorophore by coordination to an available site on the crown-complexed Ba2+ ion. 

NAND logic is also in the universal gate category, according to electronic engineers. The current inability of molecular-level counterparts to inherit this mantle has been mentioned previously in Section 2.5. NAND logic means that the output achieves the state 0 only when the inputs are both simultaneously 1. 

A NAND logic gate can be understood as an integration of NOT and AND gates where the output of the AND gate becomes the input to a NOT gate. Nice molecular examples are now available. 

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