Density functional theory study on the “Molecular Taekwondo” process of pyrene-armed calix[4]azacrowns

New calixarene derivatives pyrene-armed calix[4]azacrowns L (L1 and L2) bearing a crown ether and an azacrown ether as two binding sites are calculated systemically using density functional theory (DFT). The optimized structures and electronic properties, such as HOMO and LUMO energies, band gaps of the free ligands L (L1 and L2), the complexes L/M+ (Ag+, K+ and Cs+) and the di-cation complexes L·Ag+·M+ have been performed at B3LYP/6-31G(d) and Lanl2DZ level. Natural bond orbital (NBO) analysis is discussed on the basic of the optimized geometric structures. The results demonstrate that metal-π and metal–metal ion repulsive interactions are main driving forces of the coordination and the influence of the solvent effect is significant. Moreover, the interesting “Molecular Taekwondo” processes evolving between Ag+–K+ and Ag+–Cs+ pairs have been studied through the fluorescence change. Time-dependent density functional theory (TD-DFT) calculations on the emission spectra of the ligand L1 and compounds L1/M+ are investigated and discussed, which further evidences the existence of the metal ion exchange process.