Luminescent carbene-copper(i)-amide polymers for efficient host-free solution-processed OLEDs

Luminescent metallopolymers have attracted broad interest in the fields of healthcare and organic electronics. However, polymeric emitters based on earth-abundant metal complexes are scarce. Here, two series of Cu(i) polymers, PMAC-x and PCAAC-x (x = 1-3) have been developed using two kinds of Cu(i)-based carbene-metal-amide (CMA) complexes as side-chain emitter units to combine with a nonconjugated polystyrene backbone. These Cu(i) polymers emit via distinct thermally activated delayed fluorescence or dominant phosphorescence, inherited from the grafted Cu(i)-based CMA units. Particularly, the PMAC-x polymers exhibit high photoluminescence quantum efficiencies of up to 0.78, short emission lifetimes of down to 0.66 μs, and fast radiative rates of up to 106 s-1 in neat films. Thanks to the good encapsulation effect of the polystyrene backbone, these Cu(i) polymers not only demonstrate favorable moisture stability but also show significant aggregation-induced emission. The resultant host-free solution-processed organic light-emitting diodes (OLEDs) achieve outstanding electroluminescence performance with a record external quantum efficiency of 13.8% at a practical luminance of ∼100 nits, representing state-of-the-art device efficiency for metallopolymer-based OLEDs. This work not only presents the first example of CMA polymers but also provides the future direction of polymeric emitters from earth-abundant metal complexes for the OLED application.

Exfoliation of a Coordination Polymer Based on a Linear π-Conjugated Ligand into an Ultrathin Nanosheet for Glyphosate Sensing

Owing to the large-scale consumption of pesticides and their potential threats to the environment and human health, the development of sensing materials for pesticides has attracted considerable attention in recent years. In this work, a novel Cd(II)-based coordination polymer (CP) with the formula [Cd(H2O)2(L)]·DMF (Cd-1, DMF = N,N-dimethylformamide, H2L = 4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-benzoic acid) was synthesized under solvothermal conditions. Structural analysis revealed that coordination between central Cd2+ cations and the ligand L2- formed two-dimensional (2D) networks, which were further assembled by noncovalent hydrogen bonds into a three-dimensional (3D) supramolecular framework. Through ultrasonic treatment in isopropyl alcohol, Cd-1 was exfoliated to afford an ultrathin CP-based 2D nanosheet (Cd-1-NS) with a thickness of less than 1.8 nm. Compared to the bulk materials, the prepared Cd-1-NS exhibited enhanced fluorescence emission properties and superior sensing performance toward glyphosate (Glyph) in water with high selectivity, sensitivity, anti-interference, fast response, and good recyclability via the turn-off effect. The limit of detection (LOD) of Cd-1-NS for Glyph was as low as 41 nM (7 ppb) in the low-concentration range of 0-2.4 μM. In addition, the Cd-1-NS also showed excellent practicability and reliability for the detection of Glyph in real samples, including lake water, tap water, cabbage, and watermelon skin, and could realize the rapid visualized sensing of Glyph residues on the surfaces of vegetables and fruits.

Aggregation-Induced Enhanced Emission-Active Zinc(II) β-Diketiminate Complexes Enabling High-Performance Solution-Processable OLEDs

Earth-abundant and cheaper zinc-based organometallic molecules as luminophores are drawing significant research attention for solid-state lighting devices. In this paper, we report two air-stable zinc complexes, where the zinc is coordinated to two sterically encumbered β-diketiminate ligands in a tetrahedral geometry. In such a geometry, eight phenyl/aryl rings from the ligand backbones are oriented in a propeller shape, augmenting the restricted rotation of the putative rings. Such an architecture harnesses aggregation-induced emission behavior with an excellent solid-state emission property. The rigidity of these molecules reduces the possibility of non-radiative transitions and makes them excellent fluorescence emitters. Both molecules exhibit electroluminescence (EL) in the yellowish-green region of the visible spectrum. We have utilized these molecules as emitters to fabricate multilayered organic light-emitting diode (OLED) devices. The emitter Zn-I in host m-MTDATA exhibits EL with a maximum external quantum efficiency of 4.4%. Among the handful of zinc-based OLEDs, the performance of this emitter is very commendable with power and current efficacies of 15.2 lm W^-1 and 12.1 cd A^-1, respectively, along with a brightness of 2426 cd m^-2.

New red-emitting Schiff base chelates: promising dyes for sensing and imaging of temperature and oxygen via phosphorescence decay time

New complexes of Zn(ii), Pd(ii) and Pt(ii) with Schiff bases are prepared in a one-step condensation of 4-(dibutylamino)-2-hydroxybenzaldehyde and 4,5-diaminophthalonitrile in the presence of a metal salt. The complexes possess efficient absorption in the blue-green part of the spectrum with molar absorption coefficients up to 98 000 M-1 cm-1. The Pt(ii) complex shows very strong red phosphorescence in anoxic solutions at room temperature with a quantum yield of 65% in toluene which places it among the brightest emitters available for this spectral range. The phosphorescence of the Pd(ii) complex under the same conditions is very weak (Φ < 1%) but is enhanced to Φ > 10% upon immobilization into polymers. Optical thermometers based on self-referenced lifetime read-out are prepared upon immobilization of the dyes into gas-blocking poly(vinylidene chloride-co-acrylonitrile). At 25 °C, the materials based on Pd(ii) and Pt(ii) complexes show sensitivities of -2.1 and -0.52%τ/K, respectively. Application of the sensors for imaging of temperature on surfaces (planar optode) and for monitoring of fast temperature fluctuations (fiber-optic microsensor) is demonstrated. Immobilized into a gas-permeable matrix, the Pt(ii) complex also performs as a promising oxygen-sensing material. The new systems are also attractive for imaging of oxygen or temperature with the help of multi-photon microscopy, due to a good match with the biological optical window and much better brightness under two photon excitation compared to that of the conventional Pt(ii) meso-tetra-(pentafluorophenyl)porphyrin.