Sequence-definition in stiff conjugated oligomers

The concept of sequence-definition in the sense of polymer chemistry is introduced to conjugated, rod-like oligo(phenylene ethynylene)s via an iterative synthesis procedure. Specifically, monodisperse sequence-defined trimers and pentamers were prepared via iterative Sonogashira cross-coupling and deprotection. The reaction procedure was extended to tetra- and pentamers for the first time yielding a monodisperse pentamer with 18% and a sequence-defined pentamer with 3.2% overall yield. Furthermore, three novel trimers with a 9H-fluorene building block at predefined positions within the phenylene ethynylene chain were synthesised in 23–52% overall yields. Hence, it was confirmed that a functionality of interest can be incorporated selectively at a pre-defined position of these monodisperse oligomers. All respective intermediate structures were fully characterised by proton and carbon NMR, mass spectrometry, size-exclusion chromatography, and IR spectroscopy. Additionally, thermal and optical transitions are reported for the different oligomers.