The
Mallory reaction of 1,2-diarylhexafluorocyclopentene
(1, aryl = 3-bromophenyl; 2, aryl = 4-bromophenyl)
under light irradiation (λ = 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 π–π*
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 π-conjugation system in polymer main chains. The copolymers
showed photoluminesence (PL) in both CHCl3 and the film.