Dicarboxylic acid recognition of 1,8-bis(N,N'-diethylamidino)anthracene: NMR, X-ray, ESI-mass and fluorescence analyses of dicarboxylic acid binding complexes

Abstract

An ethyl-substituted diamidine, 1,8-bis(N,N'-diethylamidino)anthracene (1), for the recognition of dicarboxylic acids has been designed and synthesized. The complexation of diamidine 1 with dicarboxylic acids 3, 4 and α,ω−dicarboxylic acids 6 (C6-C11), showed the formation of 1:1 complexes in CH3CN. On the other hand, for the complexation with a monocarboxylic acid and α,ω−dicarboxylic acids 6 (C3-C5), formation of the amidinium 1·2H+ was observed. The crystal structures of the 1:1 complexes of the diamidine 1 and the α,ω−dicarboxylic acids 6 were obtained, and an unusual “U-shaped conformation” of 6 was observed. Furthermore, fluorescence spectra of the diamidine 1 showed “structural vibrational bands” derived from the anthracene unit after recognition of the α,ω−dicarboxylic acids (C6-C11). However, for the formation of the dissociated amidinium 1·2H+, broad fluorescence bands were observed (without a vibrational structure). Consequently, the stability of the formed complexes can be analyzed by the patterns (vibrational structures) of the fluorescence spectra.