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

Abstract

Eight random and alternating copolymers PF-DTBTA derived from 2,7-fl uorene and 4,7-dithienylbenzotriazole (DTBTA) were synthesized. Thin solid fi lms of the energy-transfer copolymers possess high absolute photoluminescence (PL) quantum yields ( Φ PL ) 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 effi ciency (EQE max ) up to 5.78%. PF-DTBTA50, the alternating copolymer, showed an orange EL with EQE max of 3.3%. The good Φ PL and EQE max of the PF-DTBTA50 with very high DTBTA content indicate that DTBTA is a high effi ciency 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 fl uorene segments to DTBTA units. Moreover, white EL devices, with forward-viewing maximum luminous effi ciency 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.

White Polymer Light‐Emitting Devices for Solid‐State Lighting: Materials, Devices, and Recent Progress

“…However, the realization of single white light‐emitting polymers is synthetically challenging. The principal strategy for the molecular design of such single white‐emitting polymers involves the covalent tethering of chromophores with either two complementary colors (blue and yellow) or three primary colors (blue, green and red) to the main or side chain, or employing hyperbranched or cross‐linked molecular framework. By fine‐tuning the chromophore content through controlling the feed ratio of monomers during copolymerization, simultaneous emission of all incorporated chromophores can be attained by managing energy transfer or charge trapping, which subsequently results in continuous broad EL spectra for the white light.…”

Red, Green, and Blue Light‐Emitting Polyfluorenes Containing a Dibenzothiophene‐S,S‐Dioxide Unit and Efficient High‐Color‐Rendering‐Index White‐Light‐Emitting Diodes Made Therefrom

“…The absorption spectra for the films closely correspond to those in solution, other than for minor red‐shifts and broadening of peaks and a more obvious long wavelength (≈515 nm) absorption in PPF‐SO15‐DHTBT1. For example, the absorption peaks at ≈440 nm and 515 nm for PPF‐SO15‐BT10 and PPF‐SO15‐DHTBT10 are some 10 nm red‐shifted in comparison to those in solution; such shifts can be ascribed to film packing effects that increase conjugation and the local dielectric constant 42. A more detailed assessment of the spectral features shows that neither replacement of dialkyl with dialkoxy‐phenyl substituents (PF to PPF) nor subsequent incorporation of SO units (PPF to PPF‐SO) has much effect on the characteristic PF π–π* transition at ≈390 nm.…”

Efficient Blue Light-Emitting Diodes Based on Conjugated Polymers with Fluorinated Silole Chemically Doped in Fluorene–Carbazole Main Chain

“…All manipulations involving air-sensitive reagents were performed under an atmosphere of dry argon. Bis[2-(3-fluorophenyl-)ethynyl]dimethylsilane, 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9,9-dioctylfluorene, and 2,7-dibromo-N-9-heptadecanylcarbazole were prepared according to the reported procedures [20,35,36]. …”