Entwined dimer formation from self-complementary bis-acridiniums

Abstract

A dicationic tweezer incorporating two acridinium moieties linked by a 2,6-diphenylpyridine spacer was shown to self-assemble in an entwined dimer both in acetonitrile and water. The reaction was studied according to solvent polarity, temperature and concentration conditions. The entwined structure was confirmed in the solid state via single-crystal X-ray diffraction.

Self-complementary and narcissistic self-sorting of bis-acridinium tweezers

“…All 1 H NMR spectrum signals of 2•2Cl (DMSO-d6, 298 K) were assigned using 2D NMR experiments (see ESI). Comparison of the 1 H NMR spectrum of 2•2Cl (c = 3 x 10 -3 mol L -1 ) to our previously reported bis-acridinium receptor 1•2Cl showed analogous chemical shifts for the acridinium protons ((H1/8) = 7.98 , (H 2/7 ) = 7.88, (H 3/6 ) = 8.45 and (H 4/5 ) = 8.90 ppm, see 13 This observation suggests that the acridinium protons of 2·2Cl are not affected by the electronic environment of the aromatic ring (phenyl or pyridyl) at their 9-position. Moreover, the spectrum of 2·2Cl did not show any signals related to the presence of its corresponding dimer as observed in 1•2Cl thus suggesting the dimer formation is less energetically favoured for (2)2·4Cl than for (1)2·4Cl.…”

“…In comparison to 1•2Cl, the relative positions of the nitrogen atoms in the spacer of 2•2Cl should not alter the optimum distance for - stacking interactions (7.1 Å) between both acridinium units. 14 In the present work, we report (i) the synthesis of a new bis-acridinium tweezer, (ii) the characterization of its self-association into an entwined dimer in water and (iii) the study of a 1:1 mixture of this new tweezer with our previously reported one (1•2Cl) 13 resulting in a narcissistic self-sorting process.…”

“…As seen for the entwined dimer formed with 1•2Cl, the cone of anisotropy of these moieties within the dimer affect each other thus explaining the observed chemical shifts in the 1 H NMR spectrum of (2)2•4Cl. 13 Further evidence of the formation of the dimer (2)2•4Cl was given by DOSY experiments (see the ESI, Fig. S2.19).…”

“…12 We recently described the synthesis of a self-complementary bis-acridinium tweezer (1•2Cl) in a five-step synthesis (Scheme 1). 13 This tweezer has shown to self-assemble into an entwined dimer in acetonitrile and water. More especially, two acridinium moieties acting as electron-deficient recognition units were able to interact through - stacking interactions with the 2,6diphenylpyridyl spacer of a second tweezer.…”

“…Scheme 1 Molecular tweezer 1•2Cl dimerizing in water. 13 We envisioned that a new self-complementary tweezer incorporating a 1,3-dipyridylbenzene spacer (2•2Cl) could lead to interesting self-association processes governed by the different electronic properties of the spacer. In comparison to 1•2Cl, the relative positions of the nitrogen atoms in the spacer of 2•2Cl should not alter the optimum distance for - stacking interactions (7.1 Å) between both acridinium units.…”