Arrangements of fluorophores in the salts of imidazole tethered anthracene derivatives with pyridinedicarboxylic acids influencing photoluminescence

Abstract

Self-assemblies of salts of 9-N-(3-imidazolylpropylamino)methylanthracene (Hanthraimida) with pyridinedicarboxylic acid and cocrystals with 1,3-dihydroxybenzenes were analysed to sort out their impacts on aggregation induced emissions in the solid state. Different structural features and proton transfers were observed in the salts and cocrystals. The salt of Hanthraimida with 2,6-pyridinedicarboxylic acid (H₂26pdc) had an unusual composition of 2[(H₃anthraimida)]²⁺[(26pdc)²⁻·2(H26pdc)⁻]·(H₂26pdc)·CH₃OH (1). This salt had hydrogen bonded anionic and neutral acid molecules that formed a chain-like arrangement, where the cations H₃anthraimida²⁺ were accommodated in two distinct supramolecular environments. On the other hand, the corresponding salt of 3,5-pyridinedicarboxylic acid (H₂35pdc) with Hanthraimida had a conventional composition of (H₃anthraimida)²⁺(35pdc)²⁻·4H₂O. The self-assembly of this salt had octameric water clusters that were hydrogen bonded to 35pdc²⁻ ions in its lattice. When such salts were prepared from solution in the presence of resorcinol, they yielded ionic cocrystals, namely [(H₃anthraimida)]²⁺[(26pdc)]²⁻·resorc·H₂O·CH₃OH (3) and 2[(H₃anthraimida)]⁺[(35pdc)]²⁻·2(resorc) (4). The self-assembly of the ionic cocrystal 3 had hydrogen bonded dimers of di-cations bridged by dicarboxylates. These dimers were bridged by water molecules to form chains, where resorcinol molecules were found as intervening molecules connecting such chains. Cocrystal 4 had two resorcinol guest molecules, one of which assembled with host ions to create space for the encapsulation of the other resorcinol molecule. DFT calculations were carried out on the neutral and ionic species to depict the possibilities of aggregation induced emissions in the solid state by 1–4. A change in the emission of the host caused by adding the two isomeric acids was indistinguishable in solution, but the corresponding solid samples of the salts had distinguishable emissions.