(BO)₂‐Doped Tetrathia[7]helicene: A Configurationally Stable Blue Emitter

Abstract

Helicenes combine two central themes in chemistry: extended π-conjugation and chirality. Heteroatom doping preserves both characteristics and allows modulation of the electronic structure of a helicene. Herein, we report the (BO) 2 -doped tetrathia[7]helicene 1, which was prepared from 2-methoxy-3,3'-bithiophene in four steps. 1 is formally derived by substituting two (Mes)BÀ O moieties in place of (H)C=C(H) fragments in two benzene rings of the parent tetrathia[7]helicene. X-ray crystallography revealed a dihedral angle of 50.26(9)°between the two terminal thiophene rings. The (P)-/(M)-1 enantiomers were separated by chiral HPLC and are configurationally stable at room temperature. The experimentally determined enantiomerization barrier of 27.4 � 0.1 kcal mol À 1 is lower than that of tetrathia[7]helicene (39.4 � 0.1 kcal mol À 1 ). The circular dichroism spectra of (P)-and (M)-1 show a perfect mirror-image relationship. 1 is a blue emitter (λ em = 411 nm) with a photoluminescence quantum efficiency of Φ PL = 6 % (cf. tetrathia [7]helicene: λ em � 405 nm, Φ PL = 5 %).

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

“…Interestingly, despite the presence of three thiophene rings, the redox potentials of H1‐Me 4 are similar to those of azabora[7]helicenes B [16a] containing a single azaborole ring. On the other hand, the reduction of H1‐Me 4 is more feasible than reduction of helicenes of type H [42] and diborylated C , [24] implying that it is more electron‐deficient than the latter compounds.…”

“…H ), [22] or their combination with cyclopentadiene and other heteroles, such as phosphole and pyrrole (compounds I ) [23] . Only recently, Licandro and Wagner reported a similar thiahelicene system where two benzene rings were replaced with 1,2‐oxaborinine heterocycles (helicene C ) [24] . This variety of thiahelicenes concludes with an extraordinary subclass of molecules assembled from angularly fused thiophene rings (e.g.…”

Substitution Effects on the Photophysical and Photoredox Properties of Tetraaza[7]helicenes

“…The research interest in helicenes has grown in recent years, driven by the increasing number of synthetic approaches [1][2][3][4][5][6][7][8] and the desire to exploit the unique properties of this class of compounds, which originate from their helical structure in combination with the extended aromatic system. Helicenes find a wide variety of applications, such as synthetic use in the preparation of chiral catalysts, often in the form of ligands, or more exotic applications including the construction of molecular machines.…”

Enantiomerization of five‐membered‐heterocycle‐embedded helicenes: A DFT study

“…16,17 Recently, theoretical calculations indicated the conformational pathway the most plausible process for helicene enantiomerization, and the transition state should be planar C 2v symmetry for [4]helicene and non-planar C s symmetry for longer helicenes, 18 and later multi-step mechanism has also been provided for longer [n]helicenes from n = 8. [19][20][21] Helicenes with five-membered heterocycles embedded on the backbone are of special interest because they could largely tune the optical and chiroptical properties, [22][23][24][25][26] form unique geometries such as sandwich-like helicene complexes and perpendicular double helicenes, [27][28][29] as well as influence the electronic properties of the helical π-conjugated system. 30 However, the enantiomerization process of these five-membered-heterocycle-embedded helicenes have not been systematically studied yet.…”

“…Helicenes with five‐membered heterocycles embedded on the backbone are of special interest because they could largely tune the optical and chiroptical properties, 22–26 form unique geometries such as sandwich‐like helicene complexes and perpendicular double helicenes, 27–29 as well as influence the electronic properties of the helical π ‐conjugated system 30 . However, the enantiomerization process of these five‐membered‐heterocycle‐embedded helicenes have not been systematically studied yet.…”