The synthesis and characterization of an enantiopure superhelicene nanographene is reported in which two saddle‐shaped and one planar hexabenzocoronene (HBC) units are arranged in a helicoidal shape ...to form an undecabenzo7carbohelicene. The described compound is the first fully π‐extended 7helicene. Racemic resolution of the helical nanographene permitted analysis of the chiroptical properties and revealed dissymmetry factors in the range of 2×10−3 both in the absorption and in the emission measurements. Remarkably, non‐linear photophysical analysis demonstrated a two‐photon absorption cross‐section of 870 GM at 800 nm and a perfect overlap between linear, non‐linear, and chiral emissions.
A twist in the ribbon: A chiral helical nanographene with a central 7helicene unit was synthesized and its enantiomers isolated and studied. Both enantiomers of the undecabenzo7superhelicene exhibit remarkable chiroptical and non‐linear optical properties, with a two‐photon absorption cross‐section of 870 GM at 800 nm and a perfect overlap between linear, non‐linear, and chiral emissions. CPL=circularly polarized luminescence.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A Triskelion‐Shaped Saddle–Helix Hybrid Nanographene Cruz, Carlos M.; Márquez, Irene R.; Castro‐Fernández, Silvia ...
Angewandte Chemie International Edition,
June 11, 2019, Volume:
58, Issue:
24
Journal Article
Peer reviewed
Open access
A unique rippled nanographene consisting of 52 fused rings is presented in which six out‐of‐plane motifs are fully fused into a triangular aromatic surface with a size of approximately 2.5 nm. Three ...units of an unprecedented fully lateral π‐extended octabenzo5helicene together with three units of saddle‐shaped heptagonal rings are combined in a single structure, leading to a well‐soluble warped nanographene. The two diastereomeric pairs of possible enantiomers were isolated, and their linear, non‐linear, and chiroptical properties were evaluated, revealing outstanding quantum yield and brightness values at low energy, together with good chiroptical responses in both absorption and emission.
Rippling the surface: A chiral nanographene consisting of four fused hexabenzocoronene‐based units was synthesized. Six curved units were introduced into a triangular aromatic surface, leading to three octabenzo5helicenes and three saddle edges. The two diastereomeric pairs of enantiomers exhibit remarkable red emission and chiroptical properties.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This feature article focuses on the bottom-up approaches (solution-phase) based on organic synthesis for the preparation of saddle-shaped distorted polycyclic aromatic hydrocarbons (PAHs). We ...summarise the recent progress on the synthetic strategies followed to obtain well-defined nanographenes containing heptagonal and octagonal carbocycles, highlighting the novel strategy developed by our group together with our recent contributions in the area of distorted aromatics. The presence of seven- or eight-membered rings induces a saddle-shape curvature in the planar network pushing the structure out of the plane, which influences the physical properties exhibited. Some brief details on the optical and electronic properties of these curved nanostructures are also discussed.
We highlight recent progress in bottom-up synthesis of well-defined distorted polyaromatic hydrocarbons with saddle shapes containing heptagonal and octagonal carbocycles.
A new family of distorted ribbon‐shaped nanographenes was designed, synthesized, and their optical and electrochemical properties were evaluated, pointing out an unprecedented correlation between ...their structural characteristics and the two‐photon absorption (TPA) responses and electrochemical band gaps. Three nanographene ribbons have been prepared: a seven‐membered‐ring‐containing nanographene presenting a tropone moiety at the edge, its full‐carbon analogue, and a purely hexagonal one. We have found that the TPA cross‐sections and the electrochemical band gaps of the seven‐membered‐ring‐containing compounds are higher and lower, respectively, than those of the fully hexagonal polycyclic aromatic hydrocarbon (PAH). Interestingly, the inclusion of additional curvature has a positive effect in terms of non‐linear optical properties of those ribbons.
The advantage of defects: The effect of a tropone moiety on the nonlinear optical properties of ribbon‐shaped nanographenes is unequivocally demonstrated. Curved edges created by the inclusion of heptagonal carbocycles enhance the two‐photon absorption on graphene molecules.
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Racemic mixtures of boronic acid-derived salicylidenehydrazone (BASHY) complexes were enantiomerically resolved. The chiroptical properties of the stereoisomers, containing an asymmetric boron as the ...only stereogenic unit, are translated into mirror-imaged electronic circular dichroism spectra and circularly polarized luminescence (CPL, dissymmetry factors of 3–5 × 10–4) is observed. The spectral position of the CPL emission is determined by the push–pull character of the dye. These features expand the functional scope of the brightly emitting BASHY dye platform.
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IJS, KILJ, NUK, PNG, UL, UM
State‐of‐the‐art chiroptical spectroscopies are valuable tools for structural elucidation. However, the potential of these spectroscopies for everyday applications has not been exploited to date ...partially due to the lack of sufficiently stable and efficient chiroptical systems. To this end, the development of suitable chiroptical structures is essential. Herein, we present the synthesis of spiro‐compounds (P2)‐1 and (P4)‐2 as well as (M2)‐1 and (M4)‐2 exhibiting remarkable chiroptical responses. Theoretical simulations show that (P2)‐1, constituted by two (P)‐configured spiranic chiral axes, presents an all‐carbon double helix structure with (M)‐helicity. On the other hand, molecular dynamic simulations reveal (P4)‐2 to have a single path for geometry‐modification along its flat conformational space, certifying it as a chiral flexible shape‐persistent macrocycle. Geometric quantification of chirality has been used to compare the spiranic derivatives presented herein.
Revealing chirality′s secrets: Diethynylspiranes have been employed for the construction of all‐carbon double helices as well as chiral flexible shape‐persistent macrocycles. The uncovering of these very diverse chiral scaffolds opens new opportunities for chiroptical applications (see scheme).
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A chiral bidentate inclusion complex has been formed by halogen-bond interaction between the pyridyl moieties of a pyridoallenoacetylenic host and octafluorodiiodobutane. X-ray crystallography showed ...that the guest adopts a chiral conformation inside the molecular channels formed by stacking of the host units. A 10 ppm shielding of the 15N NMR resonance for the pyridil units provided evidence of the formation of the halogen-bond complex in solution.
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We prove that the confinement of the conformational space of pyridoallenophanes leads to intense chiroptical responses. Unlike the cyclic dimer 142, single-conformation 141pyridoallenophanes ...isomerize under thermal and photochemical conditions. Yet, less-strained 141-bipyridoallenophanes are stable and are prepared successfully. They, unexpectedly, undergo double protonation as a result of cooperative ion-pairing and hydrogen bonding. The complex formation forces a single configuration of the axis connecting both pyridyl rings recognized by a diagnostic circular dichroism (CD) signal at 330 nm.
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The high sensitivity of chiroptical responses to conformational changes and supramolecular interactions has prompted an increasing interest in the development of chiroptical applications. However, ...prediction of and understanding the chiroptical responses of the necessary large systems may not be affordable for calculations at high levels of theory. In order to facilitate the development of chiroptical applications, methodologies capable of evaluating the chiroptical responses of large systems are necessary. The exciton chirality method has been extensively used for the interaction between two independent chromophores through the Davydov model. For systems presenting C2 or D2 symmetry, one can get the same results by applying the selection rules. In the present article, the analysis of the selection rules for systems with symmetries Cn and Dn with n = 3 and 4 is used to uncover the origin of their chiroptical responses. We foresee that the use of the Chiroptical Symmetry Analysis (CSA) for systems presenting the symmetries explored herein, as well as for systems presenting higher symmetries will serve as a useful tool for the development of chiroptical applications.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
![Undecabenzo[7]superhelicene...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1433-7851/small "Undecabenzo[7]superhelicene: A Helical Nanographene Ribbon as a Circularly Polarized Luminescence Emitter")
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