Amides as modifiable directing groups in electrophilic borylation

Amide directed C-H borylation using ≥two equiv. of BBr3 forms borenium cations containing a R2N(R')C[double bond, length as m-dash]O→B(Ar)Br unit which has significant Lewis acidity at the carbonyl carbon. This enables reduction of the amide unit to an amine using hydrosilanes. This approach can be applied sequentially in a one-pot electrophilic borylation-reduction process, which for phenyl-acetylamides generates ortho borylated compounds that can be directly oxidised to the 2-(2-aminoethyl)-phenol. Other substrates amenable to the C-H borylation-reduction sequence include mono and diamino-arenes and carbazoles. This represents a simple method to make borylated molecules that would be convoluted to access otherwise (e.g. N-octyl-1-BPin-carbazole). Substituent variation is tolerated at boron as well as in the amide unit, with diarylborenium cations also amenable to reduction. This enables a double C-H borylation-reduction-hydrolysis sequence to access B,N-polycyclic aromatic hydrocarbons (PAHs), including an example where both the boron and nitrogen centres contain functionalisable handles (N-H and B-OH). This method is therefore a useful addition to the metal-free borylation toolbox for accessing useful intermediates (ArylBPin) and novel B,N-PAHs.

Novel carbazole- and dioxino[2,3-b]pyrazine-based bipolar hosts for red PhOLEDs with a high brightness

The target compounds offer new synthetic ideas for red bipolar host materials.

4-Diphenylaminocarbazole: Switching Substituent Position for Voltage Reduction and Efficiency Enhancement of OLEDs

Simple but exceptionally efficient 4-diphenylaminocarbazole host material, 4-DPACz, is presented and compared with its positional isomer, 1-DPACz. The shift of diphenylamino substituent from the 1-position to 4-position of carbazole resulted in an increase in the HOMO energy level as well as an increase in triplet energy level. Having a high triplet energy level (2.76 eV) and well-matched HOMO energy level (-5.61 eV), 4-DPACz showed reduced driving voltage and higher efficiencies for solution-processed green PhOLEDs compated to PVK as well as 1-DPACz. Maximum luminous, power, and external quantum efficiencies reaching to 47.9 cd A^-1, 25.2 lm W^-1, and 14.3%, respectively, were achieved with a device configuration of [ITO/PEDOT:PSS/4-DPACz:Ir(mppy)₃/TPBi/CsF/Al]. Additional enhancement of efficiencies of 4-DPACz was verified when incorporating another dopant, Ir(Si-bppy)₂(acac), resulting in 59.1 cd A^-1, 29.5 lm W^-1, and 15.8%. Furthermore, reduced efficiency roll-off was clearly observed for 4-DPACz compared with PVK. Such improved device characteristics of 4-DPACz were attributed to its high hole mobility and charge balance inside the emitting layer therof. The excellent results using such a simple-structured 4-DPACz could promote various applications of this 4-DPACz unit as a building block structure for further possible oligomeric, dendritic, and polymeric materials.

Highly Efficient Phosphorescent Furo[3,2-c]pyridine Based Iridium Complexes with Tunable Emission Colors over the Whole Visible Range

A series of highly efficient phosphorescent Ir complexes with tunable emission colors over the whole visible range have been designed and synthesized based on furo[3,2-c]pyridine ligand. By mainly varying the molecular structures of the C-chelated blocks, the emission maxima of these complexes can be obviously tailored from 477 to 641 nm while keeping the considerable photoluminescence quantum yields (PLQYs) (0.55-0.78 at wavelength of 475-560 nm and 0.10-0.34 at wavelength of 590-640 nm). Correspondingly, the phosphorescent organic light-emitting diodes (OLEDs) achieve high-performance greenish-blue, green, greenish-yellow, orange, red, and deep-red electrophosphorescence, revealing state-of-art external quantum efficiences (EQEs) of 20.0% (46.6 cd/A), 31.8% (89.0 cd/A), 19.9% (71.9 cd/A), 16.6% (38.9 cd/A), 12.0% (16.7 cd/A), and 8.5% (7.3 cd/A) as well as Commision Internationale de L'Eclairage (CIE) coordinates of (0.25, 0.48), (0.30, 0.58), (0.43, 0.54), (0.62, 0.37), (0.66, 0.32), and (0.70, 0.29), respectively. The results clearly demonstrate the great potential of furo[3,2-c]pyridine based phosphors used for full-color OLED displays.

Two novel phenanthrene-based host materials in red and green organic light-emitting devices with low efficiency roll-off

Two novel phenanthrene-based host materials showed significant differences due to the different moieties at the same position of the phenanthrene backbone.

Self-Host Blue Dendrimer Comprised of Thermally Activated Delayed Fluorescence Core and Bipolar Dendrons for Efficient Solution-Processable Nondoped Electroluminescence

A self-host thermally activated delayed fluorescence (TADF) dendrimer POCz-DPS for solution-processed nondoped blue organic light-emitting diodes (OLEDs) was designed and synthesized, in which the bipolar phosphine oxide carbazole moiety was introduced by alkyl chain to ensure balanced charge transfer. The investigation of physical properties showed that the bipolar dendrons not only improve the morphological stability but also restrain the concentration quenching effect of the TADF emissive core. The spin-coated OLEDs featuring POCz-DPS as the host-free blue emitter achieved the highest external quantum efficiency (7.3%) and color purity compared with those of doped or nondoped devices based on the parent molecule DMOC-DPS, which indicates that incorporating the merits of encapsulation and bipolar dendron is an effective way to improve the electroluminescent performance of the TADF emitter used for a solution-processed nondoped device.

Intermolecular interactions boost aggregation induced emission in carbazole Schiff base derivatives

The structure–property relationship was discussed and we found that the C–H⋯π interactions and H⋯H interactions played a significant role in AIE performance.

Highly efficient triazine/carbazole-based host material for green phosphorescent organic light-emitting diodes with low efficiency roll-off

Two novel triazin/carbazole-based host materials were designed and synthesized, which demonstrated outstanding EL performance with maximum CE, PE and EQE of 69.3 cd A⁻¹, 54.2 lm W⁻¹ and 21.9%, respectively.

Metal-Catalyzed Cyclization Reactions of 2,3,4-Trien-1-ols: A Joint Experimental-Computational Study

Controlled preparation of tri- and tetrasubstituted furans, as well as carbazoles has been achieved through chemo- and regioselective metal-catalyzed cyclization reactions of cumulenic alcohols. The gold- and palladium-catalyzed cycloisomerization reactions of cumulenols, including indole-tethered 2,3,4-trien-1-ols, to trisubstituted furans was effective, due to a 5-endo-dig oxycyclization by attack of the hydroxy group onto the central cumulene double bond. In contrast, palladium-catalyzed heterocyclization/coupling reactions with 3-bromoprop-1-enes furnished tetrasubstituted furans. Also studied was the palladium-catalyzed cyclization/coupling sequence involving protected indole-tethered 2,3,4-trien-1-ols and 3-bromoprop-1-enes that exclusively generated trisubstituted carbazole derivatives. These results could be explained through a selective 6-endo-dig cumulenic hydroarylation, followed by aromatization. DFT calculations were carried out to understand this difference in reactivity.