Synthesis, Solid and Solution Studies of Paraquat Dichloride Calixarene Complexes. Molecular Modelling

the interaction of the herbicide paraquat dichloride (pq, substrate) with p-tert-butylcalix[6, 8]arenes (l, receptor) was investigated in both the solution and solid states. the isolated paraquat calixarene complexes were characterised by uv-visible, 1h nmr, esi-ms, luminescence and ir spectroscopies and elemental analysis. the stoichiometry of complexes 1 and 2 was 1:1 (1 herbicide:1 calixarene) and both revealed a biexponential luminescence decay with lifetimes depending on the size and the conformational particularity of the calixarenes. molecular modelling suggested that both calixarenes interact with the herbicide through cation-π interaction. pq is included in the p-tert-butylcalix[8]arene cavity, a situation favoured by its pinched conformation in polar solvent while it is partially included in the p-tert-butylcalix[6]arene cavity because of its in-out cone conformation. the theoretical results, in particular using mopac procedures, were in agreement with the experimental findings.