Reconfigurable Molecular Logic

In all the above cases each species was attributed with one specific logic label, but in certain circumstances one can change the coding to define different logic expressions from the same molecule. This is called as reconfigurable logic. A logic expression of a molecular gate can be changed with an optical expression by simply monitoring the gate at a different wavelength when significant input-induced spectral shifts are present. The phenomenon is known as wavelength reconfigurable logic. A DNA-binding dye 4',6'-diamidino-2-phenylindole(DAPI) (20) signals AT base pairing with a shift in the fluorescence emission spectrum. The signaling follows Watson-Crick base-pairing rules. The dye with its two phosphate receptor sites functions as a molecular NAND gate with nucleotides as inputs (Baytekin 2000). TRANSFER logic is equivalent to a YES (referring to inputj), whereby input2 is not involved with the output. Reconfiguration of molecular logic gates can also be achieved by considering different types of outputs. For example, molecule 21 has four states that are distinguishable by means of absorption and emission maxima as well as emission quantum yield and lifetime. So there is no classification until operating conditions are restricted. For this compound, if the absorbance at 440 nm is taken as the output a NAND logic function can be attributed while a 2-input INHIBIT gate, if emission is taken as the output (Rurack 2001). Extending the wavelength-reconfigurable logic leads to the idea of superposition of logic gates. This function inherits the multichannel nature of polychromatic light to obtain different, simultaneous logic expressions from the same species. All the 4 single-input functions YES, NOT, PASS0, PASS1 can be demonstrated with a non-modular chromophore-receptor system 22 (Fig. 12.8), a single H+ chemical input., and light transmittance output at carefully chosen wavelengths, because of large H+ induced displacement of the absorption band. All the 4 wavelengths can be observed simultaneously (de Silva 2002).

Fig. 12.8. Molecules exhibiting reconfigurable switching (20), TRANSFER logic (21), and SUPERPOSED logic respectively (22)

20

Fig. 12.8. Molecules exhibiting reconfigurable switching (20), TRANSFER logic (21), and SUPERPOSED logic respectively (22)

The complexity in the logic operations is also achieved using supramolecular systems with fluorophore-spacer-receptor configuration. Different logic operations such as NOT, OR etc can be integrated with this supramolecule (de Silva 1999).

Was this article helpful?

0 0
Brain Blaster

Brain Blaster

Have you ever been envious of people who seem to have no end of clever ideas, who are able to think quickly in any situation, or who seem to have flawless memories? Could it be that they're just born smarter or quicker than the rest of us? Or are there some secrets that they might know that we don't?

Get My Free Ebook


Post a comment