Chain microstructure and specific features of excitation energy transfer in solution and films of poly(9,9-dioctylfluorene) doped with 2,1,3-benzothiadiazole comonomer units

Highlights: • Copolyfluorenes of the same composition were obtained by Suzuki and Yamamoto methods. • The conjugation length of copolymers was estimated from Kerr effect data in solution. • The luminescent properties of both copolymers were quite different. • Differences in luminescent properties are due to variations of chain microstructure. • The Yamamoto type copolymer displays an efficient white electroluminescence. Spectral, luminescent and electro-optical properties of poly(9,9-dioctylfluorene), containing small quantity (1–2 mol%) of 2,1,3-benzothiadiazole comonomer units, obtained by means of either Suzuki or Yamamoto polycondensation reactions were studied and compared. The difference of luminescent properties of the two copolymers with nearly identical chemical compositions was explained by different molecular structure of their macromolecules. The films of Yamamoto type copolymer, containing, obviously, microblock sequences of 2,1,3-benzothiadiazole units, exhibit a nearly white electroluminescence (CIE x = 0.276, y = 0.274) with a high brightness (3747 cd/m² at 10 V), while the films of Suzuki type copolymer with randomly distributed isolated 2,1,3-benzothiadiazole fragments – green electroluminescence.