Efficient Synthesis of Fluorinated Phenanthrene Monomers Using Mallory Reaction and Their Copolymerization

The Mallory reaction of 1,2-diarylhexafluorocyclopentene (1, aryl = 3-bromophenyl; 2, aryl = 4-bromophenyl) under light irradiation (lambda = 365 nm) in the presence of iodide proceeded to give dibromophenanthrene derivatives, 3 and 4. Polycondensation of 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol)ester with the obtained monomers by Suzuki-Miyaura coupling afforded the phenanthrene-type copolymers Poly-3 and Poly-4 in high yields. For comparison, diphenylethene-type copolymers (Poly-1 and Poly-2) were also prepared analogously. UV-vis spectra of Poly-3 and Poly-4 in CHCl3 showed pi-pi* transition peaks at 380 and 354 nm, respectively, and additional shoulder peaks appeared at a longer wavelength in the film, suggesting the molecular assembly of the polymer molecules. In contrast, the spectra of Poly-1 and Poly 2 in solution were essentially unchanged as measured in the film, presumably owing to partial interruption of the pi-conjugation system in polymer main chains. The copolymers showed photoluminesence (PL) in both CHCl3 and the film.