Ab initio molecular orbital study of the complexing behavior of N-ethyl-1-naphthalenecarboxamide as fluorescent chemosensors for alkali and alkaline earth metal ions

N -ethyl-1-naphthalenecarboxamide (1NEa) was synthesized as a reference compound of the 1, n -bis(1-naphthalenecarboxamido)oxaalkanes (1NSN and 1NLN) having two naphthalene rings as fluorescent chemosensors for metal ions using intramolecular excimer emission. However, large changes in the fluorescence spectra of 1NEa having only one naphthalene ring as well as 1NSN and 1NLN were observed with the addition of some metal ions. Therefore, the ab initio molecular orbital calculations (Gaussian 98) using both the Hartree–Fock SCF and density functional theory methods with 6-31G and 6-31+G(d) basis sets were carried out for 1NEa and its metal complexes to investigate the complexing behavior. The results of the molecular orbital calculations suggest that 1NEa can form a complex with a metal ion by coordination with both the carbonyl oxygen of the amide group and π-electrons of the naphthalene ring.