Reversible Solvatochromism of Polydiacetylenes Based on Extensively Hydrogen-Bonded Tubular Arrays

Abstract

Since the pioneering discovery by Wagner, polydiacetylenes (PDAs) and their solvatochromic properties (typically blue-to-red or purple transitions) have been the subject of extensive research efforts. Without exception, PDAs have been found to undergo irreversible solvent-induced color changes, and no cases exist in which initial blue states of the PDAs are regenerated after solvent removal. Herein, we describe the first example of a reversibly solvatochromic PDA that is derived from a macrocyclic diacetylene (MCDA) containing four carboxylic acid moieties. Infrared spectroscopic studies confirmed the synergetic interplay of intra- and intermolecular hydrogen-bonding interactions to control the reversibility. The weak intramolecular hydrogen bonds allowed a solvent-induced distortion of the PDA backbone (purple state) by releasing unpolymerized monomers, while the strong and networked intermolecular hydrogen-bonding interactions ensured the rigidity of the tubular channels and served as the driving forces for the recovery of the initial conformation (blue state).