Efficient synthesis of discrete oligo(fluorenediacetylene)s toward chain-length-dependent optical and structural properties

Discrete oligomers are perfect candidates for understanding the structure-dependent properties of polymers. Herein, a series of discrete conjugated oligo(fluorenediacetylene)s (D-oFDAs) with a degree of polymerization (DP) up to 10 were obtained by purification with automated flash column chromatography from polydisperse polymers. It is found that the chain length can affect not only photophysical properties but also crystalline properties. As the DP of D-oFDAs increased, the longer conjugation length caused red shifts in their optical spectra and weaker crystallinity. The effective conjugation length has been extrapolated to be as long as 9 fluorenediacetylene units. Moreover, the oligomers can form uniform films by solution casting for the fabrication of light-emitting diodes, showing that the octamer has the most efficient electroluminescence (EL) properties. When the crystal of the dimer was exposed to 254 nm UV light, only part of the sample was polymerized via a 1,4-addition reaction. Significantly, the simple, scalable and effective strategy provides opportunities to further optimize the structure with diverse blocks and side chains for precisely building macromolecular architectures.