Experimental and Theoretical Structure Elucidation of the [2 : 1] Complex Ion of Carbo[n]helicene with n=6, 7 and 8 and Ag.

The front cover artwork illustrates the competition of [6]-, [7]- and [8]helicene for attaining a silver(I) cation. This struggle takes place in the electrospray process during solvent evaporation, leading to the well-known tweezer-like surrounding of Ag+ by the helicene in the [1:1] complex. In this competition, the larger helicenes outperform the smaller ones. The main topic of our investigation, however, is the resulting [2:1] complex in which a second helicene attaches via π-π stacking to the [1:1] tweezer complex. Read the full text of the Research Article at 10.1002/cphc.202300496.

Experimental and Theoretical Structure Elucidation of the [2 : 1] Complex Ion of Carbo[n]helicene with n=6, 7 and 8 and Ag.

Gas-phase complexes of [n]helicenes with n=6, 7 and 8 and the silver(I) cation are generated utilizing electrospray ionization mass spectrometry (ESI-MS). Besides the well-established [1 : 1] helicene/Ag+ -complex in which the helicene provides a tweezer-like surrounding for the Ag+ , there is also a [2 : 1] complex formed. Density functional theory (DFT) calculations in conjunction with energy-resolved collision-induced dissociation (ER-CID) experiments reveal that the second helicene attaches via π-π stacking to the first helicene, which is part of the pre-formed [1 : 1] tweezer complex with Ag+ . For polycyclic aromatic hydrocarbons (PAHs) of planar structure, the [2 : 1] complex with silver(I) is typically structured as an Ag+ -bound dimer in which the Ag+ would bind to both PAHs as the central metal ion (PAH-Ag+ -PAH). For helicenes, the Ag+ -bound dimer is of similar thermochemical stability as the π-π stacked dimer, however, it is kinetically inaccessible. Coronene (Cor) is investigated in comparison to the helicenes as an essentially planar PAH. In analogy to the π-π stacked dimer of the helicenes, the Cor-Ag+ -Cor-Cor complex is also observed. Competition experiments using [n]helicene mixtures reveal that the tweezer complexes of Ag+ are preferably formed with the larger helicenes, with n=6 being entirely ignored as the host for Ag+ in the presence of n=7 or 8.

Superhelicenes in the gas phase: experimental and computational evidence of stable radical cation dimers.

Electrospray-ionization mass spectrometry (ESI-MS) readily produces stable radical cation π-dimers of the superhelicenes. Energy-resolved collision experiments reveal the dissociation of the dicationic dimer into two singly charged superhelicenes. DFT calculations indicate that open-shell dications composed of two radical cations are thermochemically more attractive than the closed-shell dimer formed by a doubly charged and a neutral superhelicene.

A Family of Superhelicenes: Easily Tunable, Chiral Nanographenes by Merging Helicity with Planar π Systems.

We designed a straightforward synthetic route towards a full-fledged family of π-extended helicenes: superhelicenes. They have two hexa-peri-hexabenzocoronenes (HBCs) in common that are connected via a central five-membered ring. By means of structurally altering this 5-membered ring, we realized a versatile library of molecular building blocks. Not only the superhelicene structure, but also their features are tuned with ease. In-depth physico-chemical characterizations served as a proof of concept thereof. The superhelicene enantiomers were separated, their circular dichroism was measured in preliminary studies and concluded with an enantiomeric assignment. Our work was rounded-off by crystal structure analyses. Mixed stacks of M- and P-isomers led to twisted molecular wires. Using such stacks, charge-carrier mobilities were calculated, giving reason to expect outstanding hole transporting properties.

On the photophysics of nanographenes - investigation of functionalized hexa-peri-hexabenzocoronenes as model systems.

In this study, we report on hexa-peri-hexabenzocoronenes (HBCs) as representative models for nanographenes. To this end, we synthesized a family of functionalized HBCs and investigated the impact of the substituents on the π-extended systems of the HBCs. DFT and TD-DFT calculations suggested a charge transfer character, which intensified as the electron density withdrawing effects of the substituents (-M-effect) increased. Unambiguous corroboration of the charge transfer character in the case of NO2-substituents was realized via steady-state absorption and fluorescence experiments, which focused on the dependencies on the solvent polarity and temperature featuring. Going beyond HBCs with NO2-substituents, time-correlated single photon counting, and femtosecond and nanosecond transient absorption spectroscopy unveiled long-lived singlet and triplet excited states. As a complement, we performed electrochemical and spectroelectrochemical measurements. These measurements were carried out to shed light onto the nature of the functionalized HBCs as electron acceptors and/or donors, on the one hand, and their corresponding spectroscopic signatures, on the other hand. All of the aforementioned information enabled intermolecular charge separation assays with, for example, suitable electron acceptors by steady-state and time-resolved spectroscopy.

500-Fold Amplification of Small Molecule Circularly Polarised Luminescence through Circularly Polarised FRET.

Strongly dissymmetric circularly polarised (CP) luminescence from small organic molecules could transform a range of technologies, such as display devices. However, highly dissymmetric emission is usually not possible with small organic molecules, which typically give dissymmetric factors of photoluminescence (gPL ) less than 10-2 . Here we describe an almost 103 -fold chiroptical amplification of a π-extended superhelicene when embedded in an achiral conjugated polymer matrix. This combination increases the |gPL | of the superhelicene from approximately 3×10-4 in solution to 0.15 in a blend film in the solid-state. We propose that the amplification arises not simply through a chiral environment effect, but instead due to electrodynamic coupling between the electric and magnetic transition dipoles of the polymer donor and superhelicene acceptor, and subsequent CP Förster resonance energy transfer. We show that this amplification effect holds across several achiral polymer hosts and thus represents a simple and versatile approach to enhance the g-factors of small organic molecules.

Pyridinic Nanographenes by Novel Precursor Design.

In this work we present the solution-synthesis of pyridine analogues to hexa-peri-hexabenzocoronene (HBC)-which might be called superpyridines-via a novel precursor design. The key step in our strategy was the pre-formation of the C-C bonds between the 3/3' positions of the pyridine and the adjacent phenyl rings-bonds that are otherwise unreactive and difficult to close under Scholl-conditions. Apart from the synthesis of the parent compound we show that classical pyridine chemistry, namely oxidation, N-alkylation and metal-coordination is applicable to the π-extended analogue. Furthermore, we present basic physical chemical characterizations of the newly synthesized molecules. With this novel synthetic strategy, we hope to unlock the pyridine chemistry of nanographenes.

A Functional Hexaphenylbenzene Library Comprising of One, Three, and Six Peripheral Rylene-Diimide Substituents.

Synthesis and characterization of a series of rylene-diimide substituted hexaphenylbenzenes (HPBs) is presented. The direct connection of the rylene-diimide units to the HPBs via the imide-N-position without any linkers as well as the use of naphthalene-diimides (NDIs) next to perylene-diimides (PDIs) is unprecedented. While mono-substituted products were obtained by imidization reactions with amino-HPB and the respective rylene-monoimides, key step for the formation of tri- and hexa-substituted HPBs is the Co-catalysed cyclotrimerization. Particular emphasis for physic-chemical characterization was on to the number of NDIs/PDIs per HPB and the overall substitution patterns. Lastly, Scholl oxidation conditions were applied to all HPB systems to generate the corresponding hexa-peri-hexabenzocoronenes (HBCs). Importantly, the efficiency of the transformation strongly depends on the number of NDIs/PDIs. While three rylene-diimide units already hinder the Scholl reaction, the successful synthesis of mono-substituted HBCs is possible.

Hexa-peri-hexabenzocoronene decorated with an allenylidene ruthenium complex - almost a flyswatter.

Carbon-rich ruthenium allenylidene complexes bearing either a hexaarylbenzene (HAB) or a hexa-peri-hexabenzocoronene (HBC) substituent were synthesised. This was achieved via the corresponding propargyl alcohols with HAB and HBC substituents, which were accessible via 3 or 4 step reaction cascades. Reaction of the propargyl alcohols HC[triple bond, length as m-dash]C(OH)Ph(HAB) and HC[triple bond, length as m-dash]C(OH)Ph(HBC) with [RuCl(η5-C5H5)(PPh3)2] yielded the complexes [Ru(η5-C5H5)([double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]C(HAB)(Ph))(PPh3)2]PF6 and [Ru(η5-C5H5)([double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]C(HBC)(Ph))(PPh3)2]PF6. The latter of which shows interesting π-π-stacking behaviour in the solid state as well as aggregation in solution.

Oxa[7]superhelicene: A π-Extended Helical Chromophore Based on Hexa-peri-hexabenzocoronenes.

A novel π-extended "superhelicene" based on hexa-peri-hexabenzocoronenes (HBCs) has been synthesized by an efficient four-step synthetic procedure starting from diphenyl ether. Comprehensive structural analysis of the helicene was performed by NMR spectroscopy and mass spectrometry measurements together with X-ray analysis. Physicochemical analysis of the superhelicene and suitable HBC references revealed it had outstanding fluorescent features with quantum yields of over 80 %.

Highly Regioselective Alkylation of Hexabenzocoronenes: Fundamental Insights into the Covalent Chemistry of Graphene.

Hexa-peri-hexabenzocoronides (HBC) was successfully used as a model system for investigating the complex mechanism of the reductive functionalization of graphene. The well-defined molecular HBC system enabled deeper insights into the mechanism of the alkylation of reductively activated nanographenes. The separation and complete characterization of alkylation products clearly demonstrate that nanographene functionalization proceeds with exceptionally high regio- and stereoselectivities on the HBC scaffold. Experimental and theoretical studies lead to the conclusion that the intact basal graphene plane is chemically inert and addend binding can only take place at either preexisting defects or close to the periphery.

A Strategy towards the Multigram Synthesis of Uncommon Hexaarylbenzenes.

A novel rational synthetic pathway-the "functionalization of para-nitroaniline" (FpNA)-provides substituted hexaarylbenzenes (HABs) with uncommon symmetries that bear up to five different substituents, fully avoiding regioisomeric product distributions during the reactions. 4-Nitroaniline is functionalized by a cascade of electrophilic halogenations, Sandmeyer brominations, and Suzuki cross-coupling reactions, leading to 26 substitution geometries, of which 18 structures are not available by the current established techniques. Furthermore, we demonstrate that this method is applicable to the bulk production of such systems on a multigram scale. Regarding optoelectronic properties, we demonstrate how highly functionalized HABs can show strong luminescent behavior, making these molecules very attractive to organic electronic devices.