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The relationship between chemical structure and chiroptical properties is not always clearly understood. Nowadays, efforts to develop new systems with enhanced optical properties follow the trial‐error method. A large number of data would allow us to obtain more robust conclusions and guide research toward molecules with practical applications. In this sense, in this work we predict the chiroptical properties of millions of halogenated [6]helicenes in terms of the rotatory strength (R). We have used DFT calculations to randomly create derivatives including from 1 to 16 halogen atoms, that were then used as a data set to train different deep neural network models. These models allow us to i) predict the Rmax for any halogenated [6]helicene with a very low computational cost, and ii) to understand the physical reasons that favour some substitutions over others. Finally, we synthesized derivatives with higher predicted Rmax obtaining excellent correlation among the values obtained experimentally and the predicted ones. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 octabenzo[5]helicene 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. [ABSTRACT FROM AUTHOR]

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 undecabenzo[7]carbohelicene. The described compound is the first fully π‐extended [7]helicene. 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 [7]helicene unit was synthesized and its enantiomers isolated and studied. Both enantiomers of the undecabenzo[7]superhelicene 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. [ABSTRACT FROM AUTHOR]

Innenrücktitelbild: Two-Photon Absorption Enhancement by the Inclusion of a Tropone Ring in Distorted Nanographene Ribbons (Angew. Keywords: carbon materials; graphene; helicenes; nanostructures; nonlinear optics EN carbon materials graphene helicenes nanostructures nonlinear optics 7338 7338 1 04/22/20 20200427 NES 200427 B Strukturdefekte b 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. [Extracted from the article]