A diverse structural behaviour of boronated ortho-phthalaldehydes: A crystal structure of 1,3-dihydro-1,3-dihydroxy-4-formylbenzo[c][2,1]oxaborole

Two isomeric boronated ortho-phthalaldehydes 3- and 4-[B(OH)₂]-1,2-C₆H₃(CHO)₂ have been prepared and their specific behavior in solution under various conditions has been investigated using NMR spectroscopy. The former compound undergoes a ring-chain tautomeric rearrangement to form a cyclic structure of 1,3-dihydro-1,3-dihydroxy-4-formylbenzo[c][2,1]oxaborole predominating in acetone-d₆ solution and characterized by X-ray diffraction.     

2‐(Methoxy­carbonyl)phenyl­boronic acid

The structure of the title compound, 2(CH₃OCO)C₆H₄B(OH)₂ or C₈H₉BO₄, involves two crystallographically independent conformers, A and B, in a 1:2 ratio; mol­ecules of conformer A are located on a crystallographic mirror plane. The most striking difference between the two independent mol­ecules is the opposite orientation of the methoxy­carbonyl groups, while the conformations of the boronic acid groups vary more subtly. Mol­ecules of both types are ordered to produce a specific hydrogen‐bonding network that can be inter­preted in terms of a layer lying parallel to (100). Within the layer, B mol­ecules are linked with each other by two different O—H⋯O bonds to form an infinite chain where two centrosymmetric dimeric motifs can be distinguished.     

TADF Invariant of Host Polarity and Ultralong Fluorescence Lifetimes in a Donor-Acceptor Emitter Featuring a Hybrid Sulfone-Triarylboron Acceptor**

10H-Dibenzo[b,e][1,4]thiaborinine 5,5-dioxide ( SO2B )—a high triplet (T₁=3.05 eV) strongly electron-accepting boracycle was successfully utilised in thermally activated delayed fluorescence (TADF) emitters PXZ-Dipp-SO2B and CZ-Dipp-SO2B . We demonstrate the near-complete separation of highest occupied and lowest unoccupied molecular orbitals leading to a low oscillator strength of the S₁→S₀ CT transition, resulting in very long ca. 83 ns and 400 ns prompt fluorescence lifetimes for CZ-Dipp-SO2B and PXZ-Dipp-SO2B , respectively, but retaining near unity photoluminescence quantum yield. OLEDs using CZ-Dipp-SO2B as the luminescent dopant display high external quantum efficiency (EQE) of 23.3 % and maximum luminance of 18600 cd m⁻² with low efficiency roll off at high brightness. For CZ-Dipp-SO2B , reverse intersystem crossing (rISC) is mediated through the vibronic coupling of two charge transfer (CT) states, without involving the triplet local excited state (³LE), resulting in remarkable rISC rate invariance to environmental polarity and polarisability whilst giving high organic light-emitting diode (OLED) efficiency. This new form of rISC allows stable OLED performance to be achieved in different host environments.     

An ortho‐lithiated derivative of protected phenylboronic acid: an approach to ortho‐functionalized arylboronic acids and 1,3‐dihydro‐1‐hydroxybenzo[c][2,1]oxaboroles

2‐(2′‐Bromophenyl)‐6‐butyl‐[1,3,6,2]dioxazaborocan, prepared readily by the esterification of 2‐bromophenylboronic acid with N‐butyldiethanolamine (BDEA), undergoes Br/Li exchange using BuLi/THF at ? 78 °C. A resulting intermediate proved useful in synthesis of various ortho‐functionalized arylboronic acids. Specifically, reactions with benzaldehydes provide a convenient access to 1,3‐dihydro‐1‐hydroxy‐3‐arylbenzo[c][2,1]oxaboroles that exhibit a remarkably high rotational barrier around the C? aryl bond. In addition, the molecular structure of sterically hindered 1,3‐dihydro‐1‐hydroxy‐3‐(2′, 6′‐dimethoxyphenyl)benzo[c][2,1]oxaborole is reported. Copyright © 2007 John Wiley & Sons, Ltd.