4Pyridylethynyl

4-Pyridylethynyl is a chemical substituent used in organic synthesis that consists of a pyridine ring connected to an ethynyl (–C≡C–) spacer through the 4-position of the ring. In this arrangement the pyridine ring is attached at its para position to the alkyne, creating a rigid, linear linker that can couple to other molecular fragments.

The substituent provides both a pyridyl donor site and an alkyne handle. The pyridine nitrogen can act as a Lewis base and coordinate to metal centers, while the ethynyl moiety enables effective conjugation with adjacent aromatic or aliphatic groups. This combination makes 4-pyridylethynyl a versatile building block in materials science, coordination chemistry, and medicinal chemistry.

Synthesis commonly proceeds via a Sonogashira coupling using 4-halo­pyridines (such as 4-bromopyridine or 4-iodopyridine) and a terminal alkyne, in the presence of palladium catalysts and copper co-catalysts. Alternative routes include direct lithiation or other cross-coupling methods that form the C–C triple bond adjacent to the pyridyl ring.

Applications include the preparation of conjugated polymers, organic light-emitting diodes, and dye molecules where a pyridyl unit is desired for coordination or electronic coupling. It is also used to introduce pyridyl coordination sites into metal–organic frameworks and supramolecular assemblies. The term is sometimes found as pyrid-4-yl ethynyl or 4-pyridylacetylene in the literature.