A Series of Energy-Transfer Copolymers Derived from Fluorene and 4,7-Dithienylbenzotriazole for High Efficiency Yellow, Orange, and White Light-Emitting Diodes

Eight random and alternating copolymers PF‐DTBTA derived from 2,7‐fluorene and 4,7‐dithienylbenzotriazole (DTBTA) were synthesized. Thin solid films of the energy‐transfer copolymers possess high absolute photoluminescence (PL) quantum yields (ΦPL) between 60−72%. Inserting PVK layer between anode and emissive layer could show higher electroluminescence (EL) performances due to PVK‐enhanced hole injection. Random copolymers PF‐DTBTA1−15, with DTBTA molar contents from 1% to 15%, displayed yellow EL spectra with high external quantum efficiency (EQEmax) up to 5.78%. PF‐DTBTA50, the alternating copolymer, showed an orange EL with EQEmax of 3.3%. The good ΦPL and EQEmax of the PF‐DTBTA50 with very high DTBTA content indicate that DTBTA is a high efficiency chromophore with very low concentration quenching effects in the solid state PL and EL processes. PF‐DTBTA0.03−0.1 could emit white EL due to partial energy transfer from fluorene segments to DTBTA units. Moreover, white EL devices, with forward‐viewing maximum luminous efficiency up to 11 cd/A and stable white EL spectra (CIE coordinates of (0.33, 0.43)) in high current range from 5 mA to 60 mA, could be realized from the non‐doped polymer with simple binary structure. Our results suggest that DTBTA has big potential to construct high performanced EL polymers or oligomers. 4,7‐Dithienylbenzotriazole, a highly fluorescent chromophore with low concentration quenching effect, is used to construct conjugated polymers with a D‐A binary chemical structure for high efficiency yellow, orange, and white light‐emitting diodes.