Solvent-Controlled Self-Assembled Oligopyrrolic Receptor

We report a fully organic pyridine-tetrapyrrolic U-shaped acyclic receptor 10, which prefers a supramolecular pseudo-macrocyclic dimeric structure ( 10) 2 in a less polar, non-coordinating solvent (e.g., CHCl 3). Conversely, when it is crystalized from a polar, coordinating solvent (e.g., N, N-dimethylformamide, DMF), it exhibited an infinite supramolecular one-dimensional (1D) "zig-zag" polymeric chain, as inferred from the single-crystal X-ray structures. This supramolecular system acts as a potential receptor for strong acids, e.g., p-toluenesulfonic acid (PTSA), methane sulfonic acid (MSA), H 2SO 4, HNO 3, and HCl, with a prominent colorimetric response from pale yellow to deep red. The receptor can easily be recovered from the organic solution of the host-guest complex by simple aqueous washing. It was observed that relatively stronger acids with p K a < -1.92 in water were able to interact with the receptor, as inferred from 1H NMR titration in tetrahydrofuran- d 8 (THF- d 8) and ultraviolet-visible (UV-vis) spectroscopic titrations in anhydrous THF at 298 K. Therefore, this new dynamic supramolecular receptor system may have potentiality in materials science research.