Novel distyryloxadiazole-containing poly(fluorene)s and poly(p-phenylene)s with efficient energy transfer in solid state for poly(fluorene)s

Abstract 4-Bromocynnamic acid ( 1 ) was condensed with hydrazine hydrate in polyphosphoric acid to afford 2,5-di( p -bromostyryl)-1,3,4-oxadiazole ( 2 ). Two new series of soluble distyryloxadiazole-containing polyfluorenes ( PF-OXD ) and poly- p -phenylenes ( PP-OXD ) with various compositions were synthesized by Suzuki coupling utilizing 2 as a comonomer. These polymers showed optical band gaps of 2.85–2.90 eV and photoluminescence (PL) quantum yields in solution of 0.30–0.62. The solutions of polymers PF-OXD emitted blue light with PL maximum at 434–462 nm that was red shifted with the increase of the distyryloxadiazole content in the polymer. Thin films of polymers PF-OXD emitted intense green light with PL maximum around 520 nm as a result of the efficient energy transfer from the fluorene to the distyryloxadiazole segments even though the content of the latter in the polymer was 2 mol%. Polymers PP-OXD behaved as blue light emitting materials both in solution and solid state with PL maximum at 450–473 nm. Thin films of PF-OXD displayed excellent color stability even after being annealed at 100 °C for 24 h. The PL maximum of PP-OXD thin films was slightly blue shifted by 5 nm following this annealing.