Facile Two‐Step Synthesis of 1,10‐Phenanthroline‐Derived Polyaza[7]helicenes with High Fluorescence and CPL Efficiency

Otani, Takashi; Tsuyuki, Ami; Iwachi, Taiki; Someya, Satoshi; Tateno, Kotaro; Kawai, Hidetoshi; Saito, Takao; Kanyiva, Kyalo Stephen; Shibata, Takanori

doi:10.1002/ange.201700507

Cited by 67 publications

(18 citation statements)

References 52 publications

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“…Despite the strong specific rotation and CD well documented for helicenes, the CPL behavior has attracted less attention until recently [51][52][53] . The magnitude of CPL is evaluated by the luminescence dissymmetry factor (g lum ), which is defined as a relative intensity difference between left-circularly and rightcircularly polarized emission.…”

Section: Resultsmentioning

confidence: 99%

Symmetry-based rational design for boosting chiroptical responses

et al. 2018

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Chiral molecules play indispensable roles in advanced materials and technologies. Nevertheless, no conventional, yet reliable logical strategies are available for designing chiral molecules of desired chiroptical properties. Here, we propose a general protocol for rationally aligning multiple chiral units to boost the chiroptical responses, using hexahelicene as a prototype. In this proof-of-concept study, we align two hexahelicenes in various orientations and examine by theoretical calculations to predict the best chiroptical performance for X-shaped and S-shaped double hexahelicenes. We synthesize and optically resolve both double hexahelicenes and show that they exhibit more than a twofold increase in intensity of circular dichroism and circularly polarized luminescence, experimentally validating the protocol. The enhanced chiroptical responses are theoretically assignable to the electric and magnetic transition dipole moments of component hexahelicenes aligned in the correct symmetry. A guiding principle for designing advanced molecular and supramolecular chiral materials is further discussed.

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Section: Resultsmentioning

confidence: 99%

Symmetry-based rational design for boosting chiroptical responses

et al. 2018

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“…In 2017, Shibata et al reported a facile two-step synthesis of polyaza [7]helicenes possessing a 6-5-6-6-6-5-6 skeleton from commercially available 2,9-dichloro-1,10-phenanthroline via double amination with aniline derivatives followed by hypervalent iodine reagent-mediated intramolecular double-NH/CH couplings, thus yielding five different helicenic derivatives 238a-e (Scheme 56). 218 Single-crystal X-ray analysis of 238a revealed a unique structure with five significantly twisted central rings and nearly planar fused rings on both sides. This feature is different from classical helicenes where the entire skeleton possesses similar dihedral angles for the inner rims.…”

Section: Polyaza[7]helicenesmentioning

confidence: 99%

“…Frontier orbitals of 238a and ECD and CPL spectra of neutral form and acidic form of the (M) and (P) enantiomers. Adapted from ref 218. .…”

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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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“…This suggests that the restricted excited dynamics is one of the key factors to retain the large fluorescencequantum yield even in the helical form, as well as high fluorescent properties of polycyclic azaaromatic compounds. [22] Accordingly, these resultsi ndicate that the strategy of helical foldamersc onsisting of only af ew units, used in this study,i se ffective not only in promoting helix formation thermodynamically but also in suppressing nonradiative decay to construct highly fluorescent helical foldamers.…”

Section: Opticalproperties Of Dimersmentioning

confidence: 61%

“…Considering that fluorescence efficiencies in many helicalf oldamersc omposed of fluorescent units tend to decrease by intramolecular interactions such as exciplexo rC T-complex formationb etween fluorophores. [5a, 7d, 8a, 9] On the other hand, it has also been reported that the conformationalr igidification by elongation of the helical length [21] or guest binding [22] suppresses the nonradiative decay and leads to an increase in fluorescent intensity.F luorescence lifetimes of 1-3 and 16 were measured to confirmt he structurale ffect on their emission properties. The dimers 1, 2, which adopted helical forms, have longerf luorescence lifetimes owing to the decreased nonradiative decay rate (k nr ,1 .7-2.0 10 7 s À1 )compared with nonhelical 3 (2.4 10 7 s À1 )a nd monomer 16 (4.6 10 7 s À1 ), whereas the radiative decay rate (k r ) was almost the same for these compounds (1:1 0.3 10 7 s À1 ; 2: 7.7 10 7 s À1 ; 3:1 1.1 10 7 s À1 ; 16:1 0.2 10 7 s À1 ).…”

Section: Opticalproperties Of Dimersmentioning

confidence: 99%

Fluorescent Short‐Stranded Helical Foldamers Based on L‐shaped Dibenzopyrrolo[1,2‐a][1,8]naphthyridine

Tateno

Ono

Kawai

2019

Chemistry A European J

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Helical structures were constructed by using π‐spacer‐bridged dimers of dibenzopyrrolo[1,2‐a][1,8]naphthyridine, which has a highly fluorescent L‐shaped π‐extended skeleton. Three dimers with biphenylene (dimer 1), phenanthrene (dimer 2), and m‐phenylene (dimer 3) spacers, as well as a fixed‐helical dimer 4 where two quinolone rings were covalently cross‐linked, were designed and prepared. 1H NMR and ROESY spectra revealed that dimers 1 and 2 adopted helical forms in solution, whereas dimer 3 did not. The helical conformation of 1 was strengthened by addition of either polar or nonpolar solvents to the chloroform solution, which suggested that π–π stacking was the main contributor to the stabilization of the helical structure. All of the dimers, including fixed‐helical dimer 4, emitted fluorescence with high quantum yields (ϕ=0.79–0.86).

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Facile Two‐Step Synthesis of 1,10‐Phenanthroline‐Derived Polyaza[7]helicenes with High Fluorescence and CPL Efficiency

Cited by 67 publications

References 52 publications

Symmetry-based rational design for boosting chiroptical responses

Symmetry-based rational design for boosting chiroptical responses

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

Fluorescent Short‐Stranded Helical Foldamers Based on L‐shaped Dibenzopyrrolo[1,2‐a][1,8]naphthyridine

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