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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.

1, n -Bis(1-naphthalenecarboxy)oxaalkanes (1NP n N, n =1–6) and 1, n -bis(2-naphthalenecarboxy)oxaalkanes (2NP n N, n =1–6) as fluorescent sensors by excimer emission (EX) for metal ions were synthesized. We investigated the relationship between the length of the polyether chain and the metal ion recognition of NP n N (NP n N=1NP n N or 2NP n N, n =1–6) in acetonitrile solution, and the influence of the naphthalene substitution position (α-position or β-position) for metal ion recognition. Changes in the fluorescence spectra of NP n N ( n =1–3) were not observed by the addition of alkali and alkaline earth metal salts. However, the spectra of NP n N ( n =4–6) were changed by the addition of calcium and barium salts. Especially in NP n N ( n =5, 6), the changes in the shape and intensity of the fluorescence spectra were great. The values of log K for Ca 2+ and Ba 2+ were 2NP6N>1NP6N>2NP5N>1NP5N. In the cases of same length of the polyether chain, 2NP n N is an excellent fluorescent chemosensor for Ca 2+ and Ba 2+ , better than 1NP n N.