We have designed and prepared a calixarene-capped azobenzene (CCA) dimer for the uptake and controllable release of pyridinium-, ammonium-, and imidazolium-derived guest compounds. By virtue of the trans-cisphotoisomerization reaction of its azobenzene core, CCA possesses two geometrically distinct �open� and �closed� forms that can be produced in response to light.In the absence of any guest species, photoirradiation of CCA with an array of UV-emitting LEDs provides superior trans-to-cis conversion (80%) compared to other photochemical methods. We also have carried out numerous kinetics experiments for the cis to trans reversion of CCA and found that HCl dramatically accelerates this reaction and Cu2+ ion moderately accelerates it. An investigation into the mode and mechanism of this rate enhancement is underway. In terms of host-guest chemistry, trans-CCA binds weakly with a range of mono- and dications, although by 1H NMR there is little difference between the biding in the trans and cis forms. The solvent incompatibility of the nonpolar CCA host with polar guests has restricted our selection of guest species. We are addressing this challenge by (1) investigating a range of different counterions for each guest, and (2) synthesizing a functionalized analog of CCA that includes solubility-enhancing groups along the lower rims of each calixarene hemisphere.

Enhanced control of the <i>trans-cis</i> equilibrium in a calixarene-capped azobenzene dimer

247th National Meeting (2014)

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Enhanced control of the trans-cis equilibrium in a calixarene-capped azobenzene dimer