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.