Azahelicenes and other similar tri and tetracyclic helical molecules

Dumitraşcu, Florea; Dumitrescu, Dan; Aron, Ioana

doi:10.3998/ark.5550190.0011.101

Cited by 31 publications

(58 citation statements)

References 26 publications

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“…The steric strain releases by adopting either the P-or M-helix configuration. The helically extended π-conjugated system, axial chirality and associated with these structural peculiarities unique optical and electronic properties of helicenes have attracted scientific interest for decades [1][2][3][4][5][6][7][8][9][10][11]. Compared to other planar π-conjugated systems, helicenes are more thermally stable and soluble in common organic solvents [9].…”

Section: Introductionmentioning

confidence: 99%

“…Besides typical carbohelicenes, heterohelicenes, incorporating one or more heteroaromatic units in the skeleton, have also gained increasing attention [1][2][3][4][5][6][7][8][9][10][11]. The presence of heteroatoms (S, N, O, P) in the fused polycyclic π-systems additionally contributes to altering electronic structure and helps to fine tune optoelectronic properties [1][2][3][4][5][6][7][8][9][10][11]20,[35][36][37]. The last decades highlighted heterohelicenes, incorporating one or two carbazole fragments, as a very attractive class of molecules [38][39][40][41][42][43][44][45][46][47][48][49][50][51].…”

Section: Introductionmentioning

confidence: 99%

“…Carbazole-based [6]helicenes [42] and [7]helicenes [50] showed deep blue electroluminescence and have been investigated in OLED devices. Some carbazole-based [5]-and [6]helicenes have been used as visible light photoinitiators for cationic and radical polymerization [41]. [7]Helicenes of this group demonstrated a relatively high electron affinity and could be good candidates for electron-injection hole-blocking layers [39].…”

Section: Introductionmentioning

confidence: 99%

“…The classical synthetic approach for carbohelicenes is the oxidative photocyclization of stilbene derivatives [1][2][3][4][5][6][7][8][9][10][11]. The latter are generally available via the Wittig, Heck-type or McMurry couplings.…”

Section: Introductionmentioning

confidence: 99%

“…Transition-metal-catalyzed, electrophile-induced and oxidative radical cyclizations of ortho-alkynylated biaryls are widely used for the synthesis of polynuclear aromatics [57][58][59][60][61][62][63][64][65][66][67][68][69]. Recently, we have described a versatile method for the preparation of aza [4]helicenes [70], diaza [4]helicenes [70,71] and azine-fused [5]helicenes [72] through a five-step synthetic sequence, using commercially available 2,3-dihaloazines as starting materials. Based on this approach, we synthesized carbazole-based [6]helicenes fused with an azine ring (quinoxaline, pyrazine or pyridine ones).…”

Section: Introductionmentioning

confidence: 99%

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Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

Tonkoglazova¹,

Gulevskaya²,

Chistyakov³

et al. 2021

Beilstein J. Org. Chem.

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Novel carbazole-based [6]helicenes fused with an azine ring (pyridine, pyrazine or quinoxaline) have been prepared through a five-step synthetic sequence in good overall yields. Commercially available 2,3-dihaloazines were used as starting materials. To discern the effect of merging an azine moiety within a helical skeleton, the X-ray structures, UV–vis absorption and fluorescence spectra of the helicenes were investigated and compared to that of the parent carbazole-based [6]helicene (7H-phenanthro[3,4-c]carbazole).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

Tonkoglazova¹,

Gulevskaya²,

Chistyakov³

et al. 2021

Beilstein J. Org. Chem.

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Alkyne‐Based Syntheses of Carbo‐ and Heterohelicenes

Gulevskaya

Tonkoglazova

2022

Adv Synth Catal

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[n]Helicenes are polycyclic aromatic molecules in which n ortho‐condensed benzene or other aromatic rings give rise to helical chiral and highly conjugated structures. The unique screw shape, helically extended π‐system and intriguing electronic and chirooptical properties of these molecules have attracted scientific interest for decades. The applications of helicenes have now expanded into several fields including material science, nanoscience, biochemistry, supramolecular and polymer chemistry. Despite the great theoretical and practical interest in helicenes, their synthesis remains a challenge. Among synthetic approaches to helicenes, alkyne cyclizations have great potential, since carbon‐rich high‐energy alkynes can form aromatic rings via cycloisomerizations. These processes are atom‐economic. In addition, alkyne reactions are highly favorable thermodynamically. This review focuses on alkyne‐based syntheses of carbo‐ and heterohelicenes (2000–2022). These syntheses are obviously multistage. In the review, they are systematized in terms of the key step leading to the formation of a helical shape. The methods are grouped into two categories: (a) metal‐free syntheses and (b) transition‐metal‐catalyzed syntheses. This division is very arbitrary, since catalytic Sonogashira and Suzuki‐Miyaura reactions and others are often used to prepare starting materials in the syntheses of the first group. Most of the publications on the topic are related to transition‐metal‐catalyzed syntheses of helicenes.

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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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Azahelicenes and other similar tri and tetracyclic helical molecules

Cited by 31 publications

References 26 publications

Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

Alkyne‐Based Syntheses of Carbo‐ and Heterohelicenes

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

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