Synthesis and Spectroscopy of Poly(9,9-dihexylfluorene-2,7-dlyl-co-9, 9-dihexylfluorene-3,6-diyl)s and Their Model Oligomers

A series of poly(9,9-dihexylfluorene-2,7-diyl-co-9,9-dihexylfluorene-3,6-diyl)copolymers of varying composition were synthesized by Suzuki polymerization. Their composition and properties were determined by NMR, UV-vis, and fluorescence spcctroscopy and cyclic voltammetry. The incorporation of 3,6-fluorene units gives distinct blue emissions and near-UV absorptions that are blue-shifted in a nonlinear fashion as the fraction of 3,6-units increases. Sequences of 2,7-fluorene units with different lengths punctuated by 3,6-units indicate the presence of distinct chromophores. In order to better understand these changes, dimer and trimer model co-oligomers of the 2,7- and 3,6-fluorene monomers were synthesized, and their spectral properties were compared with those of the copolymers. ZINDO calculations on the models showed excellent agreement of experimental and calculated absorption spectra.