Intramolecular excimer formation and complexing behavior of 1,n-bis(naphthalenecarboxy)oxaalkanes as fluorescent chemosensors for calcium and barium ions

Abstract 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.