Self-organised nano-arrays of p-phosphonic acid functionalised higher order calixarenes

Water-soluble p-phosphonic acid calix[n]arenes (n = 5, 6 or 8) have been synthesized in five steps in overall 68, 66, 67% yield, respectively, by the recently developed procedure for p-phosphonic acid calix[4]arene. The hydrogen bonding prowess of the phosphonic acids dominates their self assembly into nano-arrays in both solution and the gas phase. In DMSO, nano-arrays of p-phosphonic acid calix[6]arene are stable for over 24 h, with the solvent molecules slowly disrupting the hydrogen bonded network affording solvated monomeric units. In the gas phase, nano-arrays of around 20 calixarene units were observed for the p-phosphonic acid calix[n]arenes using MALDI-TOF-MS, and ESI-MS revealed the presence of heteroleptic nano-arrays for a 1:1 mixture of p-phosphonic acid calix[4,5]arenes.