Appropriately Conjugated Poly[oligo(N-phenyl-2,7-carbazolylene)-alt-diphenylsilylene]s

A series of poly[oligo(2,7-carbazolylene)-alt-diphenyisilyiene]s were synthesized by Suzuki couplings by combination of basic monomers, dibromo(oligocarbazole)s, bis(dioxaborolanyl)oligocarbazoles, bis(dioxaborolanylcarbazolyl)diphenylsilanes, and bis(dioxaborolanylphenyl)diphenylsilanes. The polymers consist of the conjugated units of the dimer, trimer, pentamer, heptamer, and nonamer of the N-[p-(2-ethylhexyloxy)phenyl]carbazole-2,7-diyl and the connecting diphenylsilylene portion between the oligomer units. All of the polymers had moderate number-average molecular weights of about 14000 g/mol and good solubility in toluene. The absorption and emission maxima of these polymers in CHCl3 were in the ranges of 339-381 and 409-413 nm, respectively. A red-shift was observed as the length of the oligocarbazole unit increased less than 6 (heptamer). Poly(pentamer) and poly(heptamer) showed quantitative fluorescence quantum yields in CHCl3. The full width at half-maximum in photoluminescence spectra of these polymers in the solid state became narrower as the conjugation length got longer. The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of all of the polymers were located at about -5.6 and -2.6 eV, respectively. Investigations of polymeric light-emitting diodes having a configuration of ITO/PEDOT(PSS)/polymer/CsF/Al suggested that poly(pentamer) and poly(heptamer) had higher performances of L-max (> 8000 cd/m(2)) and eta(max) (> 0.5 cd/A) than the other poly(oligomer)s.