A series of novel carbazole-iridium copolymers have been designed and synthesized by the combination of blue-emitting acrylate carbazole M1 with hole transporting property and yellow-emitting cyclometalated iridium complex M2 containing 2-phenylpyridine as main ligand and acrylic acid as auxiliary ligand. The results showed that the blue carbazole host resulted in an efficient energy transfer to the yellow iridium complex guest, and when the feed molar ratio of M1 to M2 was 99:1, the emission spectrum of the copolymer presented a broad peak emission which can cover the whole visible range from 400 to 700 nm to obtain a nearly white copolymer material with the CIE coordinates of (0.30, 0.31), as a consequence of polymerized units luminescence, host-guest energy transfer and conjugation degree. Nevertheless, the host-guest energy transfer resulted in green emission about 524 nm of copolymer as the proportion of iridium complex monomer increased. The fluorescence quantum yields of the copolymers were significantly improved compared to the iridium complex monomer. 相似文献
Summary: A series of novel copolymers with fluorene‐alt‐carbazole segments and β‐diketonate moieties coordinating to iridium were synthesized by Suzuki polycondensation, and characterized by 1H NMR, 13C NMR, and GPC. In the absorption spectra of the copolymers, metal‐to‐ligand charge‐transfer transitions coming from iridium complex increased in intensity with increasing content of Ir complex in copolymers. The photoluminescence spectra of the copolymers were dominated by emission from the iridium complex with peak at ca. 620 nm even at the feed ratio of the complex as low as 0.5 mol‐%. The electrochemical investigation indicated that the incorporation of carbazole and iridium complex units reduce the barrier for both hole and electron injection compared with the polyfluorene. The light‐emitting diodes using the copolymers as emission layer under different device configurations were fabricated. The devices with 2‐(4‐biphenylyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole (PBD) show significantly higher external quantum efficiencies than those without PBD. A saturated red‐emitting polymer light‐emitting diode with emission peak at 628 nm, the maximum external quantum efficiency of 0.6% at the current density (J) of 38.5 mA · cm−2, and the maximum luminance of 541 cd · m−2 at 15.8 V was achieved from the device ITO/PEDOT/PFCzIrpiq3 + PBD (40%)/Ba/Al.
Novel copolymers with fluorene‐alt‐carbazole segments and iridium coordinating to β‐diketonate in the main chain. 相似文献
Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation there appears, however, an additional emission peak at around 2.3 eV, leading to both a color instability and reduced efficiency. The incorporation of the carbazole units has been proven to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate two series of alternating fluorene/carbazole oligomers and copolymers poly[2,7-(N-(2-methyl)-carbazole)-co-alt-2,7-m(9,9-dimethylfluorene)], namely, PFmCz (m = 1,2) and gain a detailed understanding of the influence of carbazole units on the electronic and optical properties of fluorene derivatives. The electronic properties of the neutral molecules, HOMO-LUMO gaps (Delta(H-L)), in addition to the positive and negative ions, are studied using B3LYP functional. The lowest excitation energies (E(g)s) and the maximal absorption wavelength lambda(abs) of PFmCz (m = 1,2) are studied, employing the time-dependent density functional theory (TD-DFT). The properties of the two copolymers, such as Delta(H-L), E(g), IPs, and EAs were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n = 0). The outcomes showed that the carbazole unit is a good electron-donating moiety for electronic materials, and the incorporation of carbazole into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of both the absorption and photoluminescence emission peaks. Most importantly, the HOMO energies of PF1Cz and PF2Cz are both a higher average (0.4 eV) than polyfluorene (PF), which directly results in the decreasing of IPs of about 0.2 eV more than PF, indicating that the carbazole units have significantly improved the hole injection properties of the copolymers. In addition, the energy gap tends to broaden and the absorption and emission peaks are gradually blue-shifted to shorter wavelengths with an increase in the carbazole content in the copolymers. This is due to the interruption of the longer conjugation length of the backbone in the (F1Cz)(n) series. 相似文献
