Synthesis and complexation properties of fluorescent calix[4]arene derivatives

Calixarenes are macrocyclic oligomers consisted of four or more phenolic residues linked by methylene bridges in the ortho position. By their relatively easy functionalization, a vast number of efficient receptors for various ionic and neutral species have been prepared [1]. Calixarenes bearing fluorescent moieties could be considered as potential sensitive fluorimetric ion sensors due to the high sensitivity of fluorimetry [2, 3]. In the scope of this work novel fluorescent antracene- and diphenylantracene-based calix[4]arene derivatives 1 and 2 were designed and synthesized. Their complexation with alkali- metal cations was investigated as well. Antracene and diphenylantracene moieties were introduced at a lower calixarene rim and served as fluorescent groups positioned close to the cation-binding site. Due to the low solubilities of the prepared calix[4]arene derivatives in solvents of moderate permittivities, their complexation was studied in methanol–dichloromethane and acetonitrile– dichloromethane solvent mixtures (φ = 0.5). Stability constants of the corresponding complexes were determined (in some cases only assessed) by means of fluorimetry, UV spectrophotometry, and isothermal microcalorimetry. The latter technique also provided information on reaction enthalpies and entropies. The obtained thermodynamic quantities were discussed regarding the structural characteristics of the ligands and solvation properties of the solvents used.