Conclusions And Further Considerations

There is one additional modification that is needed to make practical circuits. The rotation of each benzene ring would induce an alternating current in the circuit due to the changing relationship between the loop (benzene ring) and the magnetic field. This can be thought of in terms of a commercial ac electrical generator. A solution to this oscillation in current is to use molecular rectifier molecules. Rectifier molecules like the ones proposed by Aviram and Ratner (A&R) could be used to convert the alternating current to direct current.15 The placement of these rectifier molecules is shown in Figure 14. For details on the type of molecules that could be used and their proposed

Figure 14. Modified nanologic circuit schematic showing placement of molecular rectifiers.

mechanism for rectification please refer to the A&R publication.

Planarity is crucial to the proposed electrical properties of the circuit. Linking more than one circuit together using a hexatriene molecule, appears to be an effective way to limit the motion of the molecule according to the results of our simulations, especially for three or more circuits. The fact that different frequencies of light can stimulate specific rings bearing specific substituents makes possible the creation of complex circuits (logic gates, counters, etc.) through the use of multiple interconnected nanologic circuits. According to our results, the more circuits that are connected together, the more rigid the structure will be, and the more planar each nanologic circuit molecule within the structure will be.

When considering other possibilities in maintaining planarity for the circuit, we suggest another alternative to linking multiple structures together. Another way to keep the molecule flat is to place it onto a substrate. The ideal substrate will be a non-conductive surface, which will allow the nanologic circuit to stick to it preferably through hydrogen bonding or other noncovalent interactions. Furthermore, the distance between the nanologic circuit and the substrate should not be so small as to interfere with the rotation of the benzene rings. After some time and consideration, we decided to use a sheet of boron nitride.' A sheet of boron nitride is similar in structure to a sheet of graphite, with each boron being bound to 3 surrounding nitrogen atoms and each nitrogen being bound to 3 surrounding boron atoms. The lone pair electrons from each nitrogen atom can form hydrogen bonds with the hydrogen atoms on each of the polymers in the nanologic circuit molecule. A sheet of boron nitride (BN) was constructed and minimized using Hyperchem 5.01. The nanologic circuit molecule was then imported into Hyperchem in its geometry optimized state, and oriented and placed ~1.5 A above

' The use of boron nitride as a substrate was suggested to us by Dr.David Lindquist at the University of Arkansas at Little Rock.

the plane of the BN sheet. Then the whole structure was allowed to geometry optimize using the MM+ Molecular Mechanics parameter set, and the Polak-Ribiere optimization

Figure 15. A sheet of boron nitride (542 atoms) as a substrate with the nanologic circuit molecule hydrogen bonded to it in the geometry-optimized conformation.

method under Hyperchem. A picture of this optimized system can be found in Figure 15.

Molecular dynamics simulations were performed using the optimized system as a starting point. The MM+ parameter set under Hyperchem was used. The system was started out at 0 K and allowed to slowly heat up to room temp (298 K), after which it was allowed to equilibrate. Production runs were performed only after the system was equilibrated. We were interested in three things: to observe the amount of bending that would occur in the system, second, to observe if there would still be enough room for rotation of the benzene rings, and third to see if the nanologic molecule would remain on the substrate. This research is still not yet concluded. However, preliminary results suggest that this substrate/circuit molecule system does not flex very much, and it seems as though the hydrogen bonding between the nanologic molecule and the nitrogen atoms on the BN sheet is strong enough to keep the molecule onto the substrate. It is not yet clear though whether the benzene rings still undergo proper rotation, and more work needs to be done to determine this.

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