Opening Access to New Chiral Macrocycles: From Allenes to Spiranes Castro-Fernández, Silvia; Cid, María Magdalena; López, Carlos Silva ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
03/2015, Volume:
119, Issue:
9
Journal Article
Peer reviewed
Chiral macrocycles offer great potential and versatility regarding their applications. They have been employed in asymmetric catalysts, as chiral sensors, and as chiral supramolecular frameworks. For ...these reasons, they have been attracting increasing interest over the years. Despite all of the work developed in this area, most of the reported chiral macrocycles are not conformationally stable and present weak chiroptical responses. Such features substantially limit the scope of applications for these compounds. On the other hand, we have shown that axially chiral allenes can be introduced into macrocycles, conferring conformational stability and outstanding chiroptical responses. However, these allenes photoisomerize when conjugated with electron-donating groups, hampering the possibility of synthesizing systems with tuned optical properties. To overcome all of these limitations with a single structural motif, we propose the use of spiranes to construct new stable, conformationally rigid, and chemically functionalizable macrocyclic structures with strong chiroptical responses. As a first step in this new direction, we theoretically predict the chiroptical responses for macrocycles bearing spiranes to be as strong as with their allenic counterparts. As a side product, we also test the popular Minnesota functional, M06-2X, and compare it with cam-B3LYP, which has been previously analyzed with respect to experimental data in our laboratory. Thus, we hereby propose that spiranes are a good alternative to allenes for the construction of new chiral macrocycles.
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Strukturdefekte sind ein möglicher Schlüssel für Fortschritte in der Nanographen‐Technologie. E. Maçôas, A. G. Campaña et al. zeigen in ihrem Forschungsartikel auf S. 7205, wie die Einführung eines ...Carbonyl‐substituierten heptagonalen Rings (Tropon) in ein Nanographenband die Effizienz der Upconversion‐Emission bei Zweiphotonenanregung im Vergleich zu einem defektfreien Analogon erhöht. Das Ergebnis demonstriert, dass Strukturdefekte günstig für spezifische Nanographen‐Anwendungen sein können.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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.
Ein chirales helikales Nanographen mit einer zentralen 7Helicen‐Einheit wurde synthetisiert, und die Enantiomere wurden isoliert und untersucht. Beide Enantiomere des Undecabenzo7superhelicens zeigen bemerkenswerte chiroptische und nichtlineare optische Eigenschaften, mit einem Zwei‐Photonen‐ Absorptionsquerschnitt von 870 GM bei 800 nm und einem perfekten Überlapp zwischen linearen, nichtlinearen und chiralen Emissionen.
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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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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.
Ein chirales Nanographen aus vier anellierten Hexabenzocoronen‐Einheiten wurde synthetisiert. Sechs gebogene Einheiten wurden an eine dreieckige aromatische Oberfläche gebunden, wodurch drei Octabenzo5helicene und drei Sattelkanten entstanden. Die zwei diastereomeren Enantiomerenpaare emittieren im roten Spektralbereich und haben bemerkenswerte chiroptische Eigenschaften.
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Chiral molecules display a unique interaction with light. Here, it is presented the synthesis of two types of chiral structures based on spiro compounds, which show remarkable chiroptical activity. ...The structure of the (P2)‐1 molecule (depicted in dark gray) shows a double helix formed by all‐carbon atoms, while the (P4)‐2 molecule (depicted in light gray) revealed a flexible configuration that modifies its chiroptical activity, but keeps its overall peculiar structure. For more information see the Communication by H. Xu, A. G. Petrovic, J. L, Alonso‐Gómez et al. on page 11747 ff.
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Chiroptically active allenes are employed for the construction of surface-confined nanostructures. Morphological complementarity between the homochiral units leads to self-assembly of two ...highly-ordered, upstanding, diastereomeric architectures. The novel, intertwined self-assembled layer structures feature reactive terminal alkynes for further functionalization and carry potential for widespread applications exploiting chiroptical amplification.
Understanding structural defects as potential advantages is key for nanographene technology. In their Research Article on page 7139, E. Maçôas, A. G. Campaña, and co‐workers show how the introduction ...of a carbonyl‐substituted heptagonal ring (tropone ring) into a nanographene ribbon increases the efficiency of upconverted emission by two‐photon excitation in comparison with a defect‐free analogue. Therefore, structural defects are shown to be beneficial for specific nanographene applications, from materials science to biomedical applications.
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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
₂ or
₂ 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
and
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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![Undecabenzo[7]superhelicene...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0044-8249/small "Undecabenzo[7]superhelicene: A Helical Nanographene Ribbon as a Circularly Polarized Luminescence Emitter")
