Molecular-scale holes

Osmosis is the movement of solvent molecules through a semipermeable membrane. The membrane is a thin, pliable sheet of material, perforated with molecular-scale holes. The holes are large enough to allow water molecules to pass back and forth through the membrane, but too small to allow the passage of solute molecules or hydrated ions hence, the membrane is semipermeable. 

Figure 9. (a) Schematic representation of the five-module format of a photoactive triad which is switchable only by the simultaneous presence of a pair of ions. This design involves the multiple application of the ideas in Figure 1. The four distinct situations are shown. Note that the presence of each guest ion in its selective receptor only suppresses that particular electron transfer path. The mutually exclusive selectivity of each receptor is symbolized by the different hole sizes. All electron transfer activity ceases when both guest ions have been received by the appropriate receptors. The case is an AND logic gate at the molecular scale. While this uses only two ionic inputs, the principle established here should be extensible to accommodate three inputs or more, (b) An example illustrating the principles of part (a) from an extension of the aminomethyl aromatic family. The case shown applies to the situation (iv) in part (a) where both receptors are occupied. It is only then that luminescence is switched "on". Protons and sodium ions are the relevant ionic inputs.

Spectral hole-burning and molecular-scale information processing... 

Self-assembled monolayers can possess a chiral surface (see previous section) or well-defined holes on a molecular scale ( nanopores ). In the following section we indicate a recent methodology for the synkinesis of nanopores. Their use as receptor sites has as yet been extremely limited. This situation, however, is changing rapidly. 

In the context of designing molecular-scale wires, the Dexter mechanism is more relevant since it provides direct information on the propensity of the connector to conduct electrons. This mechanism involves the simultaneous transfer of an electron, by way of bridging LUMOs, and a positive hole, via the bridging HOMOs, from donor to acceptor [102]. It is a relatively short-range effect (Fig. 2.11) and, to be eflRcient, requires orbital overlap between donor and acceptor. The rate constant... 

The dual-mode sorption model considers the glassy solid to consist primarily of an equilibrium-densified matrix with a small volume fraction of uniformly distributed molecular-scale gaps, or holes, throughout the matrix. Gaps that are smaller in size than a penetrant molecule may be locally redistributed during the... 

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