No abstract

A novel electroactive star-shaped rod-coil copolymer composed of a benzene core and three symmetrically positioned tetraaniline-b-poly(ethylene glycol) arms, (TAni-b-PEG)3 rod-coil block copolymer, is synthesized successfully and characterized using Fourier transform infrared spectroscopy (FTIR), UV-vis, (1)H NMR, and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Uniform and high-quality (TAni-b-PEG)3 thin films onto indium tin oxide-coated glass surface are fabricated simply from its DMF solution. Resulting (TAni-b-PEG)3 copolymer thin films possess excellent electrochromic properties with a high optical contrast of 73.3%, superb coloration efficiency of 318.5 cm(2) C(-1) at 750 nm. Very short switching times, that is, 2.11 s and 2.14 s for coloring and bleaching times, respectively, are observed as well. The mechanism of these impressive electrochromic properties of (TAni-b-PEG)3 thin films possessed is proposed based on the atomic force microscopy investigation, star-shaped molecular geometry, synergetic electronic and ionic conductivity and amphiphilic self-assembly feature of (TAni-b-PEG)3 copolymer, which can self-assemble to form cylinder pattern consisting of quick pathways for electronic charges and ionic species, respectively.

Phosphorescent molecular aggregates show promise in realizing efficient and stable organic light‐emitting diodes (OLEDs) operating at high brightness level, which is highly desired for future lighting and display applications. Herein, four tetradentate Pd(II) complexes are prepared with judicious ligand design, and their electrochemical and photophysical properties are thoroughly examined. The studies indicate that slight structural changes of ligands can modify the hole and electron transporting capabilities, and alter the horizontal emitting dipole ratios of aggregates in amorphous film, the latter of which are sensitive to the thin‐film deposition conditions including the deposition rate and the choice of the templating layer. An optimized OLED device using Pd3O8‐Py5 aggregates exhibits a peak external quantum efficiency (EQE) of 37.3% and a reduced efficiency roll‐off with high EQEs of 36.0% and 32.5% at 1000 and 10 000 cd m−2, respectively. Moreover, such an efficient device demonstrates a long measured LT95 (time to 95% of the initial luminance) lifetime of over 500 h with an initial brightness of 17 304 cd m−2 corresponding to an estimated LT95 lifetime of 48 246 h at 1000 cd m−2.

A series of N-heterocyclic carbene (NHC)-based tetradentate Pd­(II) complexes employing phenylcarbene (Ph-NHC)-, benzocarbene (Ph/NHC)-, and pyridinocarbene (Py/NHC)-containing ligands were designed and synthesized. The NHC-based Pd­(II) complexes could be prepared by a metalation of the corresponding hexafluorophosphate ligand with Pd­(OAc)2 using K2CO3 as base in dioxane at 110 °C in 36–66% yields. All the Pd­(II) complexes are air-stable and not sensitive to moisture, and PdON5N-tt exhibits a thermal decomposition temperature (T d) of up to 416 °C. The electrochemical and photophysical properties of the Pd­(II) complexes are systematically investigated through experimental research and theoretical calculation. Their reduction potentials, frontier orbitals, and excited-state properties can be efficiently tuned through the ligand modification of the NHC moieties and also perturbed by the alkyl substituents on the pyridine and phenyl rings. Differential pulse voltammetry curves show two obvious reduction peaks for all the Pd­(II) complexes involvement with the electron-deficient alkyl pyridine and NHC moieties. Time-dependent density functional theory and natural transition orbital calculations reveal that the T1 excited-state properties are strong admixed metal-to-ligand charge-transfer (3MLCT)/ligand-centered (3LC) with some intraligand charge-transfer (3ILCT) characters for PdON5 analogues, admixed 3MLCT/3LC characters for PdON7p analogues, and admixed 3MLCT/3ILCT for PdON5N-tt. The Pd­(II) complexes emit deep-blue light in various matrixes and exhibit narrow emission spectra with a dominant peak at 437–439 nm and FWHM of 34–48 nm in dichloromethane solution and PMMA film. The Pd­(II) complexes show a PLQY and excited-state lifetime of 1–11% and 1.1–40 μs in dichloromethane, and 5–25% and 2.6–51 μs in PMMA film.

No abstract