Synthesis of a Blue‐Emissive Azaborathia[9]helicene by Silicon‐Boron Exchange from Unusual Atropisomeric Teraryls

Abstract

We report the concise synthesis and chir-(optical) properties of an azaborathia[9]helicene consisting of two thienoazaborole motifs. The key intermediate, a highly congested teraryl with nearly parallel isoquinoline moieties, was generated as a mixture of atropisomers upon fusion of the central thiophene ring of the dithienothiophene moiety. These diastereomers were characterized by single crystal X-ray analysis revealing intriguing interactions in the solid state. Subsequent insertion of boron into the aromatic scaffold via silicon-boron exchange involving triisopropylsilyl groups fixed the helical geometry, thereby establishing a novel method for the preparation of azaboroles. The ligand exchange at boron in the final step afforded the blue emitter displaying a fluorescence quantum yield of 0.17 in CH 2 Cl 2 and excellent configurational stability. Detailed structural and theoretical investigation of unusual atropisomers and the helicene provide insights into their isomerization processes.

Azaborahelicene fluorophores derived from four-coordinate N,C-boron chelates: synthesis, photophysical and chiroptical properties

“…20,[34][35][36][37][38][39][40] While carbo-[n]-helicenes and their derivatives have been an archetypical class of organic chiral systems for developing efficient CPL emitters, the introduction of a B atom with an empty p z -orbital as a functional group on chiral π-conjugated systems, or within the helical molecular systems has been shown to be an ingenious way of tuning the resulting chiral optoelectornic properties. [41][42][43][44][45][46][47][48][49][50][51][52][53] In another approach, the B atom has also been used as an anchoring unit for a chiral ligand, such as 1,1′-bi(2-naphthol) (BINOL) and its derivatives, on boron dipyrromethene (BODIPY) dyes, affording a simple and efficient way of obtaining new CPL emitters. [54][55][56][57] Our recent contributions in this research area focused on CPL-active four-coordinate N,C chelate organoboranes (Fig.…”

Benzo-Extended Heli(aminoborane)s: Inner Rim BN-Doped Helical Molecular Carbons with Remarkable Chiroptical Properties

“…In recent years, the incorporation of boron–nitrogen (BN) groups into helical skeletons, including four-coordinate BN bond (Figure b, D ) and covalent BN bond, have attracted tremendous attention, − since the BN groups tune the distribution of the frontier orbitals and endow the BN-doped helicenes with high Φ PL . ,− For example, the Φ PL of BN-embedded double [7]helicenes (Figure b, E ) reached 100%; however, the g lum value was only 0.002. Recently, an inner rim-doped BN-[6]helicene (Figure b, H ) displayed a 5-fold greater Φ PL and 15-fold greater g lum (0.0133) than its all-carbon analogue (Figure b, G ) and showed a balanced g abs of 0.0108.…”