Hydrogen‐Bonded Cyclic Tetramer Formation of a Pyridylethynylimidazole‐Based Fluorophore

Abstract Supramolecular have promising application prospects owing to their catalytic, self‐healing, and stimulus‐responsive functions. Pyridylethynylimidazole‐based supramolecular synthons with fluorescent properties have been developed. 4‐(2‐Pyridylethynyl)‐5‐arylethynyl‐1 H ‐imidazole derivatives 1 with different substituents at the 4‐ and 5‐positions of the imidazole skeleton were prepared using a step‐by‐step Sonogashira coupling reaction. The fluorescence maxima of phenyl‐ and methoxyphenyl‐substituted derivatives 1a and 1c were independent of solvent polarity. On the other hand, ester‐ and cyano‐substituted 1b and 1d showed bathochromically shifted fluorescence maxima in highly polar solvents. In crystals, the 4‐(2‐pyridylethynyl)‐5‐arylethynyl‐1 H ‐imidazole derivatives formed a supramolecular cyclic tetramer structure via two hydrogen bonds: one was between N─H in imidazole and N in pyridine, and the other was between C─H in imidazole and N in imidazole. Introducing the pyridine ring as a hydrogen bond acceptor, in addition to the imidazole ring, promoted the unique cyclic tetramer structure formation.