Chemistry Reference
In-Depth Information
that keep the components together, thereby allowing switching of energy- or
electron-transfer processes. Two-component systems of this type are reminiscent
of plug/socket electrical devices and, like their macroscopic counterparts, must be
characterized by: (1) the possibility of connecting/disconnecting the two
components in a reversible way, and (2) the occurrence of an electron or electronic
energy flow from the socket to the plug when the two components are connected.
Hydrogen-bonding interactions between ammonium ions and crown ethers are
particularly convenient for constructing molecular-level plug/socket devices,
since they can be switched on and off quickly and reversibly by means of acid-base
inputs.
A plug/socket system that deals with the transfer of electronic energy is
illustrated in Fig.
7
[
57
]. The absorption and fluorescence spectra of a CH
2
Cl
2
solution containing equal amounts of binaphthocrown ether 4 and amine 5 indicate
Fig. 7 Molecular-level plug/socket system for energy transfer based on the reversible acid-base
driven threading-dethreading motions in the hydrogen bonded pseudorotaxane 4
5H
+
(CH
2
Cl
2
;
room temperature). The acid-driven threading of compound 6, incorporating a bulky benzyl group,
through the macrocyclic cavity of 4 does not occur [
57
]
