Synthesis, Stereochemical and Photophysical Properties of Functionalized Thiahelicenes

Abstract

We report on the synthesis of a novel class of functionalized thia[6]helicenes and a thia[5]helicene, containing a benzothiophene unit and a second heteroatom embedded in the helix (i.e., nitrogen and oxygen) or a pyrene or a spirobifluorene moiety. These systems are obtained through straightforward and general procedures that involve: (i) palladium-catalyzed annulation of iodo-atropoisomers with internal alkynes and (ii) Suzuki coupling of iodo-atropoisomers with phenyl boronic acid followed by a Mallory-type reaction. Both experimental and theoretical studies on the configurational stability of some selected thia[6]helicenes confirmed their stability toward racemization at room temperature, while the pyrene-based thia[5]helicene was found to be unstable. Moreover, the configuration assignment for one representative thiahelicene was established through the comparison between experimental and theoretical circular dichroism (CD) spectra. A systematic study of the photophysical properties of both thiahelicenes and the corresponding atropoisomers has been carried out to provide a complete overview on the new molecules proposed in this work. The obtained data showed regular trends in all the thiahelicene series with spectroscopic traits in line with those previously observed for similar heterohelicenes.

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

“…The relatively small rotational strength computed for the first transition (HOMO!LUMO) is due to the fact that the electric and magnetic transition dipole moments are nearly perpendicular to each other. The CD spectrum of (M)-1 is different from those of typical helicenes [33] and thiahelicenes, [34] in that it shows only weak features in the 370-260 nm range (Figure S53), but with a more intense absorption feature for the first electronic transition (Figures S54, S55, and Tables S10, S11). This is another example for the well-known fact that the lowestenergy transitions of helicenes are substituent-sensitive, [33] while the overall shape of the spectrum is determined by the helicene backbone.…”

New advances in chiral nanographene chemistry

“…6). 58 Enantiomers of the [6]helicene structures 45a–c were able to be resolved easily via chiral HPLC, with some separated into peaks with enantiomeric purities as high as 96%. Structure 46 , with a smaller [5]helicene moiety, was too configurationally unstable to be separated in the same way, but the helical chiral structure, and the presence of two enantiomers, was unambiguously confirmed through X-ray crystallography.…”

Synthesis of Thiophene‐fused Helicenes

“…H 2 O (10 mL) and 1 M HCl (10 mL) was added, the aqueous layer was extracted with CH 2 Cl 2 (2 × 20 mL) and the combined organic layers were dried (Na 2 SO 4 ), concentrated at reduced pressure, and purified by column chromatography (silica gel, pentane) to yield 27 as a red-orange solid (315 mg, 0.658 mmol, 38 %). R f = 0.20 (pentane); 1 H NMR (500 MHz, CDCl (14), 337 (11), 226 (23) 31): Based on a published protocol, [39] K 2 CO 3 (145 mg, 1.05 mmol) was added to a solution of silane 30 (254 mg, 0.524 mmol) in CH 2 Cl 2 /MeOH (1 : 1; 20 mL) and the mixture was stirred for 21 h at rt. 1 M HCl (15 mL) was added and the aqueous layer was extracted with CH 2 Cl 2 (3 × 20 mL).…”

“…Methods applied for their preparation include photocyclizations, [9] sulfide additions to arylacetylenes, [10] [2+2+2] cycloadditions, [11] cyclizations with electrophilic sulfur reagents, [12] and McMurry olefinations [13] . These thiahelicenes [8a,14] and other structurally related helical compounds have interesting electrochemical, [15] electronic, [16] optoelectronic, [17] chiroptic, [18] supramolecular, [19] catalytic, [20] and biological [21] properties and are used in numerous applications.…”