Luminescent organic materials with high photostability are essential in optoelectronics, sensor, and photocatalysis applications. However, small organic molecules are generally sensitive to UV irradiation, giving rise to chemical decompositions. In this work, we demonstrate two novel CN-substituted twodimensional sp 2 -carbon-linked conjugated polymers (2D CCPs) containing a chromophore triphenylene unit. The Knoevenagel polymerization between 2,3,6,7,10,11-hexakis(4-formylphenyl)triphenylene (HFPTP) and 1,4-phenylenediacetonitrile (PDAN) or 2,2′-(biphenyl-4,4′-diyl)diacetonitrile (BDAN), provides the crystalline 2D CCP-HFPTP-PDAN (2D CCP-1) and 2D CCP-HFPTP-BDAN (2D CCP-2) with dual pore structures, respectively. 2D CCP-1 and 2D CCP-2 exhibit the photoluminescence quantum yield (PLQY) up to 24.9 and 32.3%, which are the highest values among the reported 2D conjugated polymers and πconjugated 2D covalent organic frameworks. Furthermore, compared with the well-known emissive small molecule tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), both 2D CCPs show superior photostability under UV irradiation for 2 h, profiting from the twisted and rigid structures of the CN-substituted vinylene linkages. The present work will trigger the further explorations of novel organic emitters embedded in 2D CCPs with high PLQY and photostability, which can be useful for optoelectronic devices.

In this work, we report on the synthesis and photophysical investigation of a new star-shaped triazine-carbazole derivative 2,4,6-tris­(3-(3,6-di-tert-butyl-9H-carbazol-9-yl)­phenyl)-1,3,5-triazine. Comparative study of the photophysical properties of the newly synthesized emitter along with its para-substituted isomer 2,4,6-tris­(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)­phenyl)-1,3,5-triazine was performed. While para-linkage caused higher oscillator strength of the lowest energy absorption band and high fluorescence quantum yield, the meta-linkage resulted in stronger charge transfer character as well as higher triplet energy. Delayed emission of meta-isomer was found to be 3 orders of magnitude more intense than that of para-isomer. Temperature dependent measurements of meta-isomer confirmed the thermally activated delayed fluorescence origin of its delayed fluorescence with the activation energy of 0.07 eV. Organic light emitting diode containing this emitter dispersed in bis­[2-(diphenylphosphino)­phenyl] ether oxide with emission spectrum peak at 475 nm was fabricated. Commission Internationale de l’Éclairage color coordinates corresponded to a sky-blue emission color (0.16, 0.23). The turn-on voltage of the electroluminescent device was found to be in the range of 5–6 V with a maximum external quantum efficiency of 9.5%. These results confirm the importance of the linking pattern between donor and acceptor moieties in the molecular design of thermally activated delayed fluorescence emitters.

Herein, a simple way of tuning the optical and structural properties of porphyrin‐based hydrogen‐bonded organic frameworks (HOFs) is reported. By inserting transition metal ions into the porphyrin cores of GTUB‐5 (p‐H8‐TPPA (5,10,15,20‐Tetrakis[p‐phenylphosphonic acid] HOF), the authors show that it is possible to generate HOFs with different band gaps, photoluminescence (PL) life times, and textural properties. The band gaps of the resulting HOFs (viz., Cu‐, Ni‐, Pd‐, and Zn‐GTUB‐5) are measured by diffuse reflectance and PL spectroscopy, as well as calculated via DFT, and the PL lifetimes are measured. Across the series, the band gaps vary over a narrow range from 1.37 to 1.62 eV, while the PL lifetimes vary over a wide range from 2.3 to 83 ns. These differences ultimately arise from metal‐induced structural changes, viz., changes in the metal‐to‐nitrogen distances, number of hydrogen bonds, and pore volumes. DFT reveals that the band gaps of Cu‐, Zn‐, and Pd‐ GTUB‐5 are governed by highest occupied/lowest unoccupied crystal orbitals (HOCO/LUCO) composed of π‐ orbitals on the porphyrin linkers, while that of Ni‐GTUB‐5 is governed by a HOCO and LUCO composed of Ni dorbitals. Overall, our findings show that metal‐insertion can be used to optimize HOFs for optoelectronics and small‐molecule capture applications.

Materials exhibiting thermally activated delayed fluorescence (TADF) have been extensively explored in the last decade. These emitters have great potential of being used in organic light-emitting diodes because they allow for high quantum efficiencies by utilizing triplet states via reverse intersystem crossing. In small molecules, this is done by spatially separating the highest occupied molecular orbital from the lowest unoccupied molecular orbital, forming an intramolecular charge-transfer (iCT) state and leading to a small energy difference between lowest excited singlet and triplet states (ΔE ST ). However, in polymer emitters, this is harder to achieve, and typical strategies usually include adding known TADF units as sidechains onto a polymer backbone. In a previous work, we proposed an alternative way to achieve a TADF polymer by repeating a non-TADF unit, polymerizing it via electron-donating carbazole moieties. The extended conjugation on the backbone reduced the ΔE ST and allowed for an efficient TADF polymer. In this work, we present a more in-depth study of the shift from a non-TADF monomer to TADF oligomers. The monomer shows non-TADF emission, and we find the delayed emission to be of triplet−triplet annihilation origin. An iCT state is formed already in the dimer, leading to a much more efficient TADF emission. This is confirmed by an almost two-fold increase of photoluminescence quantum yield, a decrease in the delayed luminescence lifetime, and the respective spectral lineshapes of the molecules.

A comprehensive study of the optical properties of CsPbBr 3 perovskite multiple quantum wells (MQW) with organic barrier layers is presented. Quantum confinement is observed by a blue-shift in absorption and emission spectra with decreasing well width and agrees well with simulations of the confinement energies. A large increase of emission intensity with thinner layers is observed, with a photoluminescence quantum yield up to 32 times higher than that of bulk layers. Amplified spontaneous emission (ASE) measurements show very low thresholds down to 7.3 μJ cm −2 for a perovskite thickness of 8.7 nm, significantly lower than previously observed for CsPbBr 3 thin-films. With their increased photoluminescence efficiency and low ASE thresholds, MQW structures with CsPbBr 3 are excellent candidates for high-efficiency perovskite-based LEDs and lasers.

Organic light‐emitting materials exhibiting thermally activated delayed fluorescence (TADF) show great promise for improving display applications. Recently, intermolecular effects between emitting molecules have been given more attention, revealing strong solid‐state solvation or aggregation induced changes of sample performance. Implications of this on device performance are not yet fully covered. In this work, a thorough investigation of a novel TADF emitter, methyl 2,3,4,5,6‐penta(carbazol‐9‐yl)benzoate (5CzCO2Me), is provided. Steady‐state emission spectra reveal a luminescence redshift with increasing emitter concentration in a small molecule host. In all investigated concentrations, the emission profile remains the same; thus, the redshift is attributed to the solid‐state solvation effect. The highest photoluminescence quantum yield (PLQY) is achieved in the 20 wt% sample, reaching 66%. The best organic light‐emitting diode (OLED) in terms of current–voltage–luminance and external quantum efficiency (EQE) parameters is the device with 60 wt% emitter concentration, reaching maximal EQE values of 7.5%. It is shown that the emitter transports holes and that charge‐carrier recombination does not take place on the bandgap of the host, but rather, a mixed host–guest concentration‐dependent recombination is seen. The hole‐transporting properties of 5CzCO2Me allow for a new dimension in tuning the device performance by controlling the emitter concentration.

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