XNOR logic gate

The XNOR logic gate combines the NOT and XOR operations (Figure 12), both of which have molecular scale counterparts. Nevertheless, only one example of this type of behavior is known, and it comes from the same stable as the case in Section 11.8. Again it involves pseudorotaxane chemistry (see Chapters 7 and 8), produced this time from components 27 and 28. 71 ... 

Fig. 12 An XNOR logic gate and its corresponding truth table.

Tetrathiafulvalene-containing systems have also been reported. One such pseudorotaxane represents a redox-active system in which a similar molecular motion can be controlled by two different inputs. Reversible dethreading-rethread-ing cycles involving this product can be performed by either oxidation and consecutive reduction of the linear component or reduction and consecutive oxidation of the electron-accepting cyclophane tetracation. As such, the system corresponds to a further level of sophistication in systems of this type. Formally, the input (elec-trochemical)/output (absorption spectrum) characteristics of this assembly correspond to those of an XNOR logic gate. 

Table 2. Truth tables for a an NAND, b an NOR, c an XOR, and d an XNOR logic gate...

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