On the Physicochemical Properties of Pyridohelicenes

Chocholoušová, Jana Vacek; Vacek, Jaroslav; Andronova, Angelina; Míšek, Jiří; Songis, Olivier; Šámal, Michal; Stará̈, Irena G.; Meyer, Michel; Bourdillon, Mélanie; Pospı́šil, Lubomı́r; Starý, Ivo

doi:10.1002/chem.201204410

Cited by 25 publications

(22 citation statements)

References 105 publications

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“…Because [4]helicene has a small racemization barrier of 14.6 to 31.8 kJ mol −1 as calculated with different methods, the stereoisomers resulting from the different helicity of the [4]helicene moieties can in principle interconvert rapidly with each other in solution at room temperature. In contrast, the different helicities of the [5]helicene moieties in 2 a and b are expected to result in stable isomers that can be isolated at room temperature because [5]helicene has a much higher racemization barrier (calculated with different methods as 95.0 to 133.9 kJ mol −1 and experimentally determined as 95.0 kJ mol −1 ) . To determine the stereochemistry of 2 a and b , red crystals of 2 a were grown from solution of 1,2‐dichloroethane/ethyl acetate and were subjected to X‐ray diffraction.…”

Section: Resultsmentioning

confidence: 99%

“…Single crystals of this orange compound were grown from CH 2 Cl 2 /ethyl acetate and were subjected to X‐ray diffraction. The crystal structure reveals an achiral stereoisomer of 2 b with anti ‐folded conformation . Figure a shows the backbone of anti ‐ 2 b , which has the ( M , P )‐( P , M , P , M ) helicity and is more curved than twisted‐ 2 a in the [5]helicene moieties with a larger dihedral angle.…”

Section: Resultsmentioning

confidence: 99%

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Twisted Polycyclic Arenes from Tetranaphthyldiphenylbenzenes by Controlling the Scholl Reaction with Substituents

Yong

Yuan

Shan

et al. 2016

Chemistry A European J

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Herein, we report two new types of twisted polycyclic arenes (2 a, b and 3 a, b) with constitutionally isomeric π-backbones, which are synthesized by controlling the Scholl reaction of 1,2,4,5-tetra(naphth-2-yl)-3,6-diphenylbenzene (1) with properly positioned electron-donating substituents. With a polycyclic backbone containing two [5]helicene and four [4]helicene moieties, 2 a and b are new members of multiple helicenes with interesting stereochemistries. The as-synthesized 2 a and b are the twisted isomers, and thermal isomerization of twisted-2 b results in anti-2 b, a more stable stereoisomer. Both twisted- and anti-2 b have been fully characterized, and the thermal isomerization of twisted-2 b has been studied with H NMR spectroscopy and DFT calculations. Compounds 3 a and b are new members of twistacenes, the benzannulated pentacene backbone of which exhibits an end-to-end twist as found from the crystal structure. Twisted- and anti-2 b are also found to function as p-type semiconductors in solution-processed thin film transistors, whereas the thin films of 3 b appear insulating presumably due to the lack of π-π interactions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Twisted Polycyclic Arenes from Tetranaphthyldiphenylbenzenes by Controlling the Scholl Reaction with Substituents

Yong

Yuan

Shan

et al. 2016

Chemistry A European J

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“…Thus, the barrier to racemisation of pyrene‐based dibenzo[7]helicene (+)/(−)‐ 1 is higher than those of [7]helicene (+)/(−)‐ 15 (42.5 kcal mol −1 )23 and dibenzo[7]helicene (+)/(−)‐ 16 (40.9 kcal mol −1 ),10a the half‐lives of which are about 12 h (at 239 °C) and 5 h (at 230 °C), respectively. Obviously, the presence of tert ‐butylated pyrene moieties at the termini of the helical backbone increases the steric congestion in the transition state for racemisation, and therefore its barrier height is influenced not only by the embedded [7]helicene subunit, but also by the lateral extension of the helicene scaffold comprising tert ‐butyl groups (in a C 2 ‐symmetric transition‐state model) 24…”

Section: Resultsmentioning

confidence: 99%

Chimerical Pyrene‐Based [7]Helicenes as Twisted Polycondensed Aromatics

Buchta

Rybáček

Jančařík

et al. 2015

Chemistry A European J

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Chimerical pyrene-based dibenzo[7]helicene rac-1 and 2H-pyran[7]helicene (M,R,R)-(-)-2, in which two pyrene subunits are fused to the [7]helicene/[7]heterohelicene scaffold, were synthesised by means of Ni(0) - or Co(I) -mediated [2+2+2] cycloisomerisation of dipyrenyl-acetylene-derived triynes. Pyrene-based dibenzo[7]helicene 1 was obtained in enantioenriched form by enantioselective cycloisomerisation under Ni(0) /QUINAP catalysis (57 % ee) or in enantiopure form by racemate resolution by liquid chromatography on a chiral column. 1,3-Allylic-type strain-controlled diastereoselective cycloisomerisation was employed in the synthesis of enantiopure (M,R,R)-(-)-2. Physicochemical properties of 1 and 2 encompassing the helicity assignment, stability to racemisation, X-ray crystal structure, UV/Vis, experimental/calculated electronic circular dichroism and fluorescence spectra were studied. Accordingly, comparison of the X-ray crystal structure of (M,R,R)-(-)-2 with calculated structures (DFT: B3LYP/cc-pVDZ, B97D/cc-pVDZ) indicated that its helical backbone is slightly over-flattened owing to intramolecular dispersion forces between tert-butylated pyrene subunits. Both 1 and 2 are fluorescent (with quantum yields in dichloromethane of ΦF =0.10 and 0.17, respectively) and are suggested to form intramolecular excimer states upon excitation, which are remarkably stabilised and exhibit large Stokes shifts (296 and 203 nm, respectively).

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“…This has been also observed by Stary and Stara in 2014. 91 Table 4. Activation parameters of the enantiomerization of aza [5]helicenes 35a 1-7 , carbo [5]helicene 36, and carbo [6]helicene 3 obtained by DHPLC 90 together with calculated enantiomerization barriers.…”

Section: Oxidative Photocyclizationmentioning

confidence: 99%

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

2019

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In this review, we discuss the rich chemistry of helicenes and helicenoids containing maingroup elements. Enantioenriched helicenic derivatives containing main-group elements B, Si, N and P, either incorporated within the helical backbone or grafted to it, will be thoroughly presented. We will describe their synthesis, resolution, and asymmetric synthesis, their structural features, electronic and chiroptical properties, emission, together with other photochemical properties and applications. OUTLINE 14 The absorption spectrum of 19c recorded in CH 2 Cl 2 solutions exhibited a maximum at 376 nm which is significantly red shifted compared with that of double [5]helicene 19a (310 nm) due to the more extended π-conjugation in 19c. According to TD-DFT calculations, the low-energy absorption band from 400 to 500 nm is assignable to the HOMO→LUMO transition corresponding to a π−π* transition of the fully conjugated bis-helical system. DFT calculations revealed a very high theoretical isomerization barrier of 45.1 kcal/mol for the (P,P)/(M,M)-19c stereoisomer, i.e. 4.4 kcal/mol higher than the (P,M) stereoisomer (not observed experimentally). The high configurational stability of 19c enabled to obtain the pure (P,P)and (M,M)-19c by chiral HPLC (Daicel Chiralcel IE column; EtOAc/MeOH = 9:1 as eluent) and to study their chiroptical properties. The ECD spectrum of (P,P)-19c in CH 2 Cl 2 displayed two strong positive bands at 275 and 320 nm, a strong negative one at 375 nm and a broad and less intense one between 425-475 nm. 52 Note that the isomerization barrier of the OBO-fused double [7]helicene is much higher than for oxabora[6]helicene 9 (vide supra) and higher than carbo[7]helicene (42.0 kcal/ mol), indicating the advantage of double helicenes over monohelicenes in terms of conformational stability. Indeed no racemization was observed upon heating enantiomer (P,P) and (M,M)-19c for 24 h up to 200 °C. 52 Note that in 2017 a longer double OBO-helicene analogue was deposited on a Au(111) under UHV conditions and its surface-assisted cyclodehydrogenation into a planar OBO-perihexacene was observed by STM. 54 Similarly to 6 and 9, the strong bond alternation found in the BOC4 rings of 19a 51 may account for the small NICS value of 1.3 while the surrounding C6 rings, including the distorted central benzene ring, show large negative NICS values (Scheme 3c). For comparison, in the all-carbon analogue tetrabenzo-[a,f,j,o]perylene shown in Scheme 3c, the central C6 ring shows a positive NICS value, indicating substantial antiaromatic character. Notably, molecular orbital calculations of 19a indicate that the HOMO and LUMO are spread over the C6 rings rather than on the boron and oxygen atoms, accounting for the substantial stability of 19a (Scheme 3c). Borahelicenes are efficient blue fluorophores. Indeed, azabora[6]helicene 6 displays blue fluorescence at 447 nm (Table 2), while smaller achiral [4]helicenic systems were successfully used as host materials in phosphorescent OLEDs with efficiencies better than the classical 4,4'...

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On the Physicochemical Properties of Pyridohelicenes

Cited by 25 publications

References 105 publications

Twisted Polycyclic Arenes from Tetranaphthyldiphenylbenzenes by Controlling the Scholl Reaction with Substituents

Twisted Polycyclic Arenes from Tetranaphthyldiphenylbenzenes by Controlling the Scholl Reaction with Substituents

Chimerical Pyrene‐Based [7]Helicenes as Twisted Polycondensed Aromatics

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

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