Fluorescent ratiometry of tetrahomodioxacalix[4]arene pyrenylamides upon cation complexation

C-1,2-alternate tetrahomodioxacalix[4]arene pyreneamides were synthesized. Pb2+ coordination gave a quenched monomer and excimer fluorescence emission, while upon Ca2+ ion binding, the receptor provides an enhanced excimer and declined monomer emission with ratiometric response. The excimer emission spectra changes are rationalized by frontier molecular orbitals that the effective Py-Py* interaction induces emission intensity increases upon Ca2+ ion complexation, whereas there is no such interaction observed upon Pb2+ binding.