Proton Catenates

For the [3]catenand 10, four successive protonation reactions are observed via absorption and luminescence spectroscopy [66]. Interestingly, after the first protonation step a nonsymmetrical proton catenate is formed, where one moiety is protonated and the other is free. In this case, luminescence quenching of the unproto-nated subunit by the protonated one is found, most likely by energy transfer. 

The effect of interlocking on the properties of molecules is dramatic. For example, the basicity of the 2,9-diphenyl-1.10-phenanthroline unit is enhanced by several orders of magnitude when it is present in a [2]catenand. The proton catenate displays a similar molecular structure to that of the corresponding copper(I) catenate, whereas that of the catenand is completely different. The special topology of the catenands and knots makes them unique ligands, with strong complexes being formed with a variety of metal ions. ° ... 

At the top of the ladder of the catenating power, thore are esters of strong protonic acids (superacids) like CF3SO3R, FSO3R, CISO3R, etc. 

For the [2]catenand 5, two clearly distinct protonation reactions are found, and it was demonstrated unambiguously that both protonated forms have a catenate structure [60, 67], i.e., the two dap fragments are arranged in an entwined structure identical to that involved for metal catenates. The driving force for this unexpected behavior is likely to be the nn electronic donor-acceptor interactions between phenathroline and anisyl fragments that can be established only in the catenate-type arrangement, and not in a open form. The luminescence properties of 5 and its protonated forms H-S" " and (H2).5 are reported in Table 9. 

As far as the external action is concerned, several external stimuli can be conveniently used to achieve rotation of one ring into the other some success has been achieved by chemical means like addition of protons [60, 89, 90], demetalation of catenates [90, 91] or change of solvent [85], but by far the most convenient system for its ease of control is a redox action which can be either chemically, electro-chemically, or photochemically induced. The latter method, based on light-induced electron transfer processes, could take advantage of the development of laser technology and grant a complete control both in the space and in the time domain. 

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