Efficient blue organic light-emittng diodes based on pyrene phenanthrimidazole and D-π-A chromophore

Robust luminogens as cutting-edge tools for efficient light emission in recent decades

Blue luminogens play a vital role in white lighting and potential metal-free fluorescent materials and their high-lying excited states contribute to harvesting triplet excitons in devices. However, in TADF-OLEDs (ΔEST < 0.1 eV), although T1 excitons transfer to S1via RISC with 100% IQE, the longer lifetime of blue TADF suffers from efficiency roll-off (RO). In this case, hybridized local and charge transfer (HLCT) materials have attracted significant interest in lighting owing to their 100% hot exciton harvesting and enhanced efficiency. Both academics and industrialists widely use the HLCT strategy to improve the efficiency of fluorescent organic light-emitting diodes (FOLEDs) by harvesting dark triplet excitons through the RISC process. Aggregation-induced emissive materials (AIEgens) possess tight packing in the aggregation state, and twisted AIEgens with HLCT behaviour have a shortened conjugation length, inducing blue emission and making them suitable candidates for OLED applications. TTA-OLEDs are used in commercial BOLEDs because of their moderate efficiency and reasonable operation lifetime. In this review, we discuss the devices based on TTA fluorophores, TADF fluorophores, HLCT fluorophores, AIEgens and HLCT-sensitized fluorophores (HLCT-SF), which break through the statistical limitations.

Ultrasound-Assisted Synthesis of Chalcone: A Highly Sensitive and Selective Fluorescent Chemosensor for the Detection of Fe3+ in Aqueous Media

The chalcone compound DHPO was synthesized through a chemical reaction between 1-(2-hydroxyphenyl)-ethanone and 3,4-dimethoxy benzaldehyde under ultrasound irradiation. The interaction between the DHPO compound and several metal ions was studied using fluorescence behavior, revealing that the chalcone function as a "turn on and turn off" switch fluorescent sensor, for selectively and sensitively detecting Fe3+ ions. The process of fluorescence quenching and complexation of DHPO with Fe3+ ion was further studied using methods such as Benesi-Hildebrand, Stern-Volmer plot, and job plot.

Neat synthesis of isothiazole compounds, and studies on their synthetic applications and photophysical properties

Ammonium thiocyanate-promoted simple, rapid and eco-friendly neat synthesis of isothiazoles is developed for the first time.

Blue organic light-emitting diodes with hybridized local and charge-transfer excited state realizing high external quantum efficiency

Donor-spacer-acceptor (D-π-A) materials CAPI and CCAPI, with hybridized local and charge transfer (HLCT) emissive states, have been synthesized. The twisting D-π-A architecture promotes the partial separation of HOMO and LUMO, leading to an enhanced % CT component, and the anthracene moiety in CAPI and CCAPI increases the conjugation length, leading to an enhanced % LE component. The non-doped device with CCAPIb shows the blue emission (450 nm) with maximum current efficiency (η c), power efficiency (η p), and external quantum efficiency (η ex) of 16.83 cd A-1, 15.32 lm W-1, and 12.0%, respectively, as well as exciton utilization efficiency (EUE) of 95% with a luminance of 32 546 cd m-2 and a roll-off efficiency of 0.53%. The new design strategy has great potential for developing high-performance blue electroluminescent materials.

En Route Towards the Control of Luminescent, Optically-Active 3D Architectures

π-Extended systems are key components for the development of future organic electronic technologies. While conceiving molecules with improved properties is fundamental for the evolution of materials science, keeping control over the 3D arrangement of molecules represents an ever-expanding challenge. Herein, a synthetic protocol to replace carbon atoms of π-systems by dissymmetric phosphorus atoms is reported; in particular, it allowed for conceiving new fused phosphapyrene derivatives with improved properties. The presence of dissymmetric phosphorus atoms precluded the formation of excimers. X-ray diffraction revealed that, meanwhile, strong intermolecular interactions are taking place in the solid state. The phosphapyrenes photoluminesce in the visible region with high quantum yields; importantly, they are CD-active. In addition, the unique non-planar features of phosphorus atoms allowed for the control of the 3D arrangement of molecules, rendering lemniscate-like structures. Based on our discoveries, we envisage the possibility to construct higher-order, chiral 3D architectures from larger phosphorus-containing π-systems.

Asymmetrically twisted phenanthrimidazole derivatives as host materials for blue fluorescent, green and red phosphorescent OLEDs

The electroluminescent properties of asymmetrically twisted phenanthrimidazole derivatives comprised of fluorescent anthracene or pyrene unit namely, 1-(1-(anthracen-10-yl)naphthalen-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (ANSPI), 1-(1-(pyren-1-yl) naphthalene-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (PNSPI), 4-(2-(4-(anthracen-9-yl) styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (ASPINC) and 4-(2-(4-(pyren-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (PSPINC) for blue OLEDs have been analyzed. The asymmetrically twisted conformation interrupt π-conjugation effectively results in deep-blue emission. The pyrene containing PSPINC based non-doped blue device (476 nm) shows maximium efficiencies (current efficiency (ηc)-4.23 cd/A; power efficiency (ηp)-2.86 lm/W; external quantum efficiency (ηex)-3.48%: CIE (0.16, 0.17) at 3.10 V. Among the doped blue devices, An(PPI)2:ASPINC shows high efficiencies (ηc-12.13 cd/A; ηp-5.98 lm/W; ηex-6.79%; L-23986 cd m-2; EL-458 nm) at 3.15 V with CIE (0.15, 0.17) than An(PPI)2:PSPINC based device which is inconsistent with non-doped device performances. The green and red PhOLEDs show higher efficiencies with Ir(ppy)3: ASPINC (ηc-50.6 cd/A; ηp-53.4 lm/W; ηex-17.0%; L-61581 cd m-2; EL-501 nm, CIE (0.31, 0.60) at 3.32 V and (bt)2Ir(dipba): ASPINC (ηc-15.2 cd/A; ηp-16.5 lm/W; ηex-14.5%; L-13456 cd m-2; EL-610 nm), CIE (0.63, 0.36) at 3.20 V, respectively. The complete energy transfer between the host and dopant molecules improved the efficiency of PHOLEDs.