2,7-carbazole-based conjugated polymers for blue, green, and red light emission

Light-emitting 2,7-carbazole-based homopolymers and copolymers were prepared by Yamamoto or Suzuki cross-coupling reaction. Poly(N-(2-ethylhexyl)-2,7-carbazole) (PEHC), poly(N-octadecyl-2,7-carbazole) (PODC), and poly(N-(2-ethylhexyl)-2,7-carbazole-alt-4-heptyl-2,5-pyridine) (PCPy) emit blue light while poly(N-(2-ethylhexyl)-2,7-carbazole-alt-2,3-diheptyl-5,8-quinoxaline) (PCQ) and poly(N-(2 ethylhexyl)-2,7-carbazole-alt-3,3',4''',3""-tetramethyl-3",4"-dihexyl-2,2':5',2":5",2''':5''',2""-quinquethiophene-1",1"-dioxide) (PCPTO) emit green and red light, respectively. The fluorescence quantum yield in chloroform solution ranges from 25% for PCPTO to 83% for PCQ. All these 2,7-carbazole-based polymers do not show any evidence of excimer formation in the solid state. Most of these polymers exhibit a glass transition at ca. 60-70 degreesC with a degradation temperature above 385 degreesC. These new polymeric materials should allow the development of efficient blue-, green-, and red-light-emitting diodes with improved optical stability.