Calix[2]thia[4]phyrin: An Expanded Calixphyrin with Aggregation-Induced Enhanced Emission and Anion Receptor Properties

The synthesis of
calix[2]­thia[4]­phyrin 3, a core-modified
expanded calixphyrin, by an efficient synthetic route is reported. 3 exhibits an aggregation-induced enhanced emission (AIEE)
phenomenon upon addition of increasing amounts of water. This is attributed
to the restricted intramolecular rotation of the meso-aryl rings present on the sp3 bridging carbons. SEM studies
revealed the formation of aggregation in an acetonitrile/water mixture
with an average diameter of the aggregate in the range 0.38–2.08
μm. The photoluminescence quantum yield of 3 in
9:1 water/acetonitrile is 5-fold higher than the quantum yield in
acetonitrile alone. Single-crystal X-ray analysis of 3 revealed a chairlike conformation stabilized by N–H···N
and C–H···π intramolecular hydrogen-bonding
interactions. Fluorine atoms on the meso-pentafluorophenyl
groups are involved in C–H···F intermolecular
hydrogen-bonding interactions to generate a two-dimensional supramolecular
assembly in the solid state. In the diprotonated state, 3 has affinity for anions and forms 1:1 complexes with SO42–, NO3–, Cl–, and ClO4– in solution. The tetrahedral
anions bind more strongly than the other anions. Single-crystal X-ray
structure studies of the ClO4– anion
complex with 3 revealed the formation of both 1:1 and
1:2 complexes in the solid state, with the host and the guest being
held together by N–H···O hydrogen-bonding interactions.