(9-Phenyl-9H-carbazol-2-yl)boronic acid

Technical Specifications

Product Description & Scientific Applications

(9-Phenyl-9H-carbazol-2-yl)boronic acid is an arylboronic acid in which boron is bonded at the 2-position of a carbazole that carries a phenyl group on its nitrogen (the 9-position).

Suzuki–Miyaura coupling. In palladium-catalysed Suzuki–Miyaura cross-coupling the boronic acid is the nucleophilic partner, transferring the 9-phenylcarbazol-2-yl group to an aryl or heteroaryl halide to form a new carbon–carbon bond. Carbazole-2-boronic acids serve in this role: a carbazole-2,7-diboronic acid, for example, couples with an aryl bromide to give the 2,7-diarylcarbazole.

The 2-position. The carbazole's 3,6-positions are the ones that readily react with electrophiles, so the 2-position is not the default site of functionalisation; a pre-formed 2-boronic acid gives direct access to the carbazole long (2,7) axis. Where the ring is joined sets its electronic behaviour: substitution at the 2,7-positions narrows the band gap more than substitution at the 3,6-positions. In otherwise identical carbazole copolymers the 2,7-connected isomer absorbs at lower energy than the 3,6-connected isomer and shows a hole mobility about an order of magnitude higher, together with a more suitable highest-occupied-molecular-orbital level for extracting holes.

Optoelectronic materials. Carbazole-based conjugated polymers are used across organic electronics for their tunable optical and electrical properties. Poly(3,6-carbazole) derivatives have been applied in organic light-emitting diodes and show redox, nonlinear-optical and photorefractive activity, while 2,7-carbazole copolymers generally outperform their 3,6-counterparts in organic field-effect transistors, bulk-heterojunction solar cells, and thermoelectric and electrical-memory devices. As a solution-processable hole-transport layer in perovskite solar cells, a 2,7-carbazole copolymer reached 4.47% power-conversion efficiency, exceeding the 3,6-linked analogue.

Host materials. Carbazole is also a standard host for guest emitters in phosphorescent organic light-emitting devices, a role that requires the wide band gap and high triplet energy needed to prevent energy back-transfer from the dye. That high triplet energy originates in the reduced aromaticity of the central five-membered ring, which weakens conjugation between it and the flanking benzene rings; extending conjugation, as the 2,7-axis does, lowers it. This boronic acid therefore builds the conjugation-extended, charge-transporting members of the carbazole family rather than wide-gap hosts.

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