One‐Step Borylation of 1,3‐Diaryloxybenzenes Towards Efficient Materials for Organic Light‐Emitting Diodes

Abstract

The development of a one‐step borylation of 1,3‐diaryloxybenzenes, yielding novel boron‐containing polycyclic aromatic compounds, is reported. The resulting boron‐containing compounds possess high singlet‐triplet excitation energies as a result of localized frontier molecular orbitals induced by boron and oxygen. Using these compounds as a host material, we successfully prepared phosphorescent organic light‐emitting diodes exhibiting high efficiency and adequate lifetimes. Moreover, using the present one‐step borylation, we succeeded in the synthesis of an efficient, thermally activated delayed fluorescence emitter and boron‐fused benzo[6]helicene.

Directly Diphenylborane‐Fused Porphyrins

“…[1] While the porphyrinylboranes are kinetically stable owing to the steric protection of the large aryl groups,t hey display only marginally perturbed optical and electrochemical properties because of their twisted conformations.T oe nhance electronic interactions between ap orphyrin and ab oron atom, we envisioned diphenylborane-fused porphyrins 1M and 2Ni (Scheme 1), in which the meso-boron atom is embedded in afused skeleton to force the p-orbital of the boron atom to strongly interact with the p-electronic network of the porphyrin. One of the trimethylsilyl groups in 3Ni is convertible into aB Br 2 group by an Si-B exchange reaction with BBr 3 [4] and then the second C À Bbond can be formed by an intramolecular bora-Friedel-Crafts reaction [5] at the nucleophilic meso-carbon atom. [2] As imple synthetic route to 1M would involve an initial installation of ab oron atom at the meso-position and as ubsequent oxidative fusion reaction.…”

“…[3] However,s uch an oxidative route is not suitable for the synthesis of 1M because ar equired intermediate, meso-diphenylborylporphyrin, would be unstable even under ambient conditions.H ence, we designed an ew synthetic route toward 1Ni via the key intermediate 3Ni bearing an unsubstituted meso-position and two trimethylsilylphenyl groups (Scheme 1). One of the trimethylsilyl groups in 3Ni is convertible into aB Br 2 group by an Si-B exchange reaction with BBr 3[4] and then the second C À Bbond can be formed by an intramolecular bora-Friedel-Crafts reaction [5] at the nucleophilic meso-carbon atom. Finally,aring-closing Si-B exchange reaction at the other trimethylsilyl group should furnish 1Ni (see Scheme S1 in the Supported Information for detailed plausible mechanism).Porphyrin 3Ni was synthesized from 3,7-diiodoporphyrin [6] by Negishi cross-coupling reaction with 2-trimethylsilylphenylzinc chloride [7] in the presence of aP d 2 (dba) 3 /2dicyclohexylphosphino-2',6'-diisopropoxybiphenyl (Ruphos) catalysis.…”

“…[4] and then the second C À Bbond can be formed by an intramolecular bora-Friedel-Crafts reaction [5] at the nucleophilic meso-carbon atom. Finally,aring-closing Si-B exchange reaction at the other trimethylsilyl group should furnish 1Ni (see Scheme S1 in the Supported Information for detailed plausible mechanism).…”

Polycyclic Aromatic Hydrocarbon Derivatives toward Ideal Electron-Transporting Materials for Organic Light-Emitting Diodes

“…The other one is the phenanthroline unit, and high μ e s of (5.8–4.4) × 10 –3 cm 2 /(Vs) have been demonstrated for diphenanthroline derivatives with moderate triplet energy around 2.4 eV . Moreover, a potential way to balance charge mobility with high triplet energy may be the recently emerged heteroatom embedded polycyclic aromatic compounds. , Boron-containing polycyclic aromatic compounds have receives a lot of attention recently. One example is 5,9-dioxa-13b-boranaphtho­[3,2,1-de]­anthracene, which possesses a high triplet energy of 2.97 eV .…”

“…Moreover, a potential way to balance charge mobility with high triplet energy may be the recently emerged heteroatom embedded polycyclic aromatic compounds. , Boron-containing polycyclic aromatic compounds have receives a lot of attention recently. One example is 5,9-dioxa-13b-boranaphtho­[3,2,1-de]­anthracene, which possesses a high triplet energy of 2.97 eV . Owing to the existence of the electron-deficit B atom, it is reasonable to envisage that derivatives based on this unit can be used as ETMs with high T 1 and high mobilities.…”