Conjugated nanohoops, such as [n]cycloparaphenylenes ([n]CPPs) and derivatives, exhibit unique structural and optoelectronic properties, making them promising candidates for applications in optoelectronic materials, and as hosts for supramolecular chemistry. Using π-systems unsymmetric to rotation or incorporating chiral units can furnish chiral nanohoops. We herein present the synthesis and characterization of diketo[8]- and diketo[9]CPPs, along with their corresponding dibenzo[a,e]pentalene (DBP) derivatives, DBP[8]- and DBP[9]CPP. Due to the central chirality of the diketone-units, these nanohoops are chiral without the possibility of racemization through rotation and show distinct chiroptical properties. The diketo[n]CPPs possess high fluorescence quantum yields of 87% (n = 8) and 92% (n = 9). The shape-adaptive properties of diketo[n]CPPs, facilitated by the tunable kink angle of the diketo unit, enable efficient host-guest interactions with fullerenes. Fluorescence titration revealed a similar binding constant for both fullerenes C60 and C70 (5 × 104 to 7 × 104 M-1 in toluene), corroborated by DFT calculations that illustrate adaptive changes in nanohoop geometry upon fullerene complexation. ESI-MS is employed to generate ionized [1 : 1] host-guest complexes of diketo[9]CPP and DBP[9]CPP with C60 and C70 as guests. The relative stabilities of these complexes are evaluated in energy-resolved collision experiments.

The peculiar solid-state packing of a peropyrene-linked and CPP-based double nanohoop is known from earlier studies to hinder the desired formation of 1 : 2 complexes with C60. In proof-of-concept experiments presented in this work, we provide evidence of the elusive 1 : 2 complex by employing electrospray ionization mass spectrometry. Additionally, for the first time, a binary 1 : 2 ring-in-ring complex of the double nanohoop with [6]CPP is observed. Most remarkably, we succeeded in generating a stable 1 : 2 complex accommodating the cationic endohedral metallofullerenes Li+@C60 as guest molecules, only the second reported example of a 1 : 2 host-guest complex involving Li+@C60 and the first within a CPP-based double nanohoop architecture. Evidently, the noncovalent attractive bonding exceeds the Coulomb repulsion of the two positive charges. These findings demonstrate that the intrinsic binding capability of the host is not fundamentally limited to 1 : 1 complexation but rather constrained by solid-state packing effects, suggesting that rational crystal engineering may enable access to such doubly occupied architectures in the condensed phase.

Carbon nanohoops are promising precursors for the bottom-up synthesis of carbon nanotubes, whose structural dynamics are not well understood despite their desirable materials properties. Here, we investigate the conformational landscape and energetics of cycloparaphenylenes (CPPs) and similar derivatives, including a methylene-bridged CPP and a carbon nanobelt. These nanohoops can form host-guest complexes with other rings, and understanding the dynamics of such assemblies is crucial for predicting their properties and identifying their potential applications. We used a combination of ion mobility mass spectrometry, tandem mass spectrometry, density-functional theory calculations and collision cross section simulations to characterise the single nanohoops and their ring-in-ring complexes, following their energetics and the conformational landscape of their disassembly from intact complexes to fragment ions. Our results show both rings and ring-in-ring complexes possess structural rigidity and reveal interesting trends in size, packing density, stability, and structure between [6]CPP, the methylene-bridged CPP and the carbon nanobelt as guests in ring-in-ring complexes, showing how mass spectrometry data can help to unravel the rules that govern the formation of such assemblies.

The host–guest chemistry of the double N -heterotriangulene-[5]helicene and C 60,70 is reminiscent of a molecular helter skelter. The noncovalent nanographene–fullerene complexes are prime examples of concave–convex shape complementarity.

We report the synthesis and comprehensive characterization of a dimethylmethylene-bridged N-heterotriangulene (N-HTA) with diaminotriazinyl groups to guide the self-assembly through directional hydrogen bonding. Mass spectrometry collision-induced dissociation experiments indicated the formation of multiply charged clusters in the gas phase. Single crystal X-ray diffraction studies revealed that the solid state packing is governed by an interplay between the hydrogen bonding and the solvent system used for crystallization. The self-assembly on both semiconducting and insulating surfaces upon simple drop-casting was disclosed by atomic force microscopy and scanning tunneling microscopy. The strong hydrogen bonding leads to robust self-assembly on surfaces, which can be conveniently achieved by simple solution processing techniques under ambient conditions.

Cobalt dioxolenes are a well-known class of switchable coordination compounds showing an intramolecular electron transfer, which is always accompanied by a spin state change at the cobalt center. Here, we present the very first example of such bistable species where an intramolecular electron transfer does take place, but the spin state change is suppressed.

Chiral carbon nanodots (CNDs) were fabricated through the hydrothermal processing of sulfanilic acid and chiral tartaric acid, exhibiting outstanding catalytic performance for the chiral catalysis of the ring-opening reaction. Furthermore, the catalytic mechanism was proposed to understand the link between the chiral structure and the performance of the catalyst.

[2]Rotaxanes offer unique opportunities for studying and modulating charge separation and energy transfer, because the mechanical bond allows the robust, yet spatially dynamic tethering of photoactive groups. In this work, we synthesized [2]rotaxane triads comprising a central (aza)[10]CPP⊃C60 bis-adduct complex and two zinc porphyrin stoppers to address how the movable nanohoop affects light-induced charge separation and energy transfer between the rotaxane subcomponents. We found that neither the parent nanohoop [10]CPP nor its electron-deficient analogue aza[10]CPP actively participate in charge separation. In contrast, the nanohoops completely prevented through-space charge separation. This result is likely due to supramolecular "shielding", because charge separation was observed in the thread that acted as reference dyad. On the other hand, the suppression of electron transfer allowed the observation of energy transfer from the porphyrin triplet to the fullerene triplet state with a lifetime of ca. 25 μs. The presence of the interlocked nanohoops therefore leads to a dramatic switch between charge separation and energy transfer. We suggest that our results explain observations made by others in photovoltaic devices comprising nanohoops and may pave the way toward strategic uses of mechanically interlocked architectures in devices that feature (triplet) energy transfer.

Carbon nanohoops are promising precursors for the synthesis of nanotubes, whose structural dynamics are not well understood. Here, we investigate the conformational landscape and energetics of cycloparaphenylenes (CPPs), a methylene-bridged CPP and a carbon nanobelt. These nanohoops can form host-guest complexes with other rings, and understanding their structure is crucial for predicting their properties and identifying potential applications. We used a combination of ion mobility, tandem mass spectrometry, and density functional theory to characterize the nanohoops and their ring-in-ring complexes, following the energetics and conformations of their disassembly from intact complexes to fragment ions. Our results show structural integrity of the nanohoops and host-guest complexes. They also reveal interesting trends in size, packing density, stability, and structure between [6]CPP, the methylene-bridged CPP, and the carbon nanobelt as guests in ring-in-ring complexes. Taken together, our work illustrates how mass spectrometry data can help to unravel the rules that govern the formation of carbon nanohoop assemblies.

[n]Cycloparaphenylenes ([n]CPPs) are strained macrocycles, comprising only sp2-hybridized carbon atoms. In recent years, [n]CPPs have become of great research interest in the field of supramolecular chemistry since their special structure enables the formation of novel host-guest complexes. In this work, we investigate the gas-phase chemistry of noncovalent complexes of [10-12]CPP with the pristine fullerenes C76/78/84 and the endohedral metallofullerenes (EMFs) Sc3N@D3h-C78, Sc3N@D5h-C80 and M3N@Ih-C80 (M = Sc, Y, Lu, Gd). The [1 : 1] complexes with [10-12]CPP are detected as radical cations. The stability and charge distributions of these complexes are studied using energy-resolved collision-induced dissociation (ER-CID). Our results assess the size complementarity, the influence of fullerene symmetry and size as well as the role of the metal size inside the EMF on the binding affinity and complex stability. Two main trends in complex stability have been found: First, [10-12]CPP form more stable complexes with EMFs than with pristine fullerenes and second, all complexes of EMFs with the C80 skeleton show similar stability despite the different metal clusters encapsulated. Another major finding is the fact that [11]CPP is generally the most suitable host for fullerenes with a C76/78/80/84 skeleton. Considering the charge distributions, we observe the existence of two different fragmentation channels for complexes with EMFs where the radical cation is either located at the CPP or at the EMF: (1) [n]CPP+(center dot) + EMF and (2) [n]CPP + EMF+(center dot). This behavior allows a clear distinction of the cage isomers ([11]CPP superset of Sc3N@Ih-C80)+(center dot) and ([11]CPP superset of Sc3N@D5h-C80)+(center dot) in the MS2 experiment. The experimental results are accompanied by density functional theory (DFT) calculations of ionization potentials (IPs) and fragmentation energies. The computational results fully confirm the measured order of complex stabilities and explain the prevalence of EMF or CPP signals in the spectra by the trend in ionization potentials.

Triphenylamine (TPA) and N-heterotriangulene (N-HTA) scaffolds with up to three oligophenyl extensions are investigated by electrospray ionization (tandem) mass spectrometry (ESI-[MS/]MS). Due to their low oxidation potentials, all molecules readily form radical cations in the electrospray process. The energy-resolved collision-induced dissociation behaviour of the molecular ions is contrasted to that of the silver(I) adducts. Complexation with Ag(I) leads to the expected [1:1] and [2:1] complexes (MAg+ and M2Ag+); however, even [1:2] complexes (MAg2 2+) can be detected for molecules with two and three large π-expansions to allow stabilization of two charges. The TPA scaffolds decompose only at high collision energies through the loss of peripheral tert-butyl groups. A general mechanism for this is proposed commencing with a methyl loss and followed by the release of isobutene and butyl radical moieties. The N-HTA-based scaffolds are considerably less stable and molecular ions fragment at low collision energies. This is caused by the facile loss of methyl radicals from the dimethylmethylene-bridged triangulene core. In contrast, complexation with Ag+ leads to a dramatic stabilization. Most interestingly, dissociation eventually proceeds via the loss of neutral AgCH3, which is indicative of strong bidentate, tweezer-like bonding of Ag+ to the molecules.

Intramolecular electron transfer without accompanying spin-crossover in cobalt bis-dioxolenes has been observed for the first time.

The Front Cover illustrates the competition of [6]-, [7]- and [8]helicene for attaining a silver(I) cation during solvent evaporation in electrospray ionization. In this competition, the larger helicenes outperform the smaller ones. This first step is eventually leading to the formation of a [2:1] complex in which one helicene is attached via π–π stacking to a [1:1] tweezer complex. Cover design by Christoph Oleszak. More information can be found in the Research Article by Thomas Drewello and co-workers.

Deriving diverse compound libraries from a single substrate in high yields remains to be a challenge in cycloparaphenylene chemistry. In here, a strategy for the late-stage functionalization of shape-persistent alkyne-containing cycloparaphenylene has been explored using readily available azides. The copper-free [3+2]azide-alkyne cycloaddition provided high yields (>90 %) in a single reaction step. Systematic variation of the azides from electron-rich to -deficient shines light on how peripheral substitution influences the characteristics of the resulting adducts. We find that among the most affected properties are the molecular shape, the oxidation potential, excited-state features, and affinities towards different fullerenes. Joint experimental and theoretical results are presented including calculations with the state-of-the-art, artificial intelligence-enhanced quantum mechanical method 1 (AIQM1).

The supramolecular chemistry of cycloparaphenylenes (CPPs) is characterized by the ability of the ring system to undergo both concave and convex π-π interactions. As a consequence, ring-in-ring complexes can be formed in which the CPP serves as the host as well as the guest molecule ([n + x]CPP⊃[n]CPP). In this work, host-guest ring-in-ring complexes of [n]CPPs (n = 5-12) are investigated by means of electrospray ionization-tandem mass spectrometry (ESI-MS2) and laser desorption ionization mass spectrometry (LDI-MS). Extending the experimentally known complexes with ring size differences of five and six phenyl units (x = 5 and 6), we observe complexes with ring size differences of three up to seven phenyl units (x = 3-7). Energy-resolved collision experiments reveal that the charge is mainly located at the inner ring and complexes with phenyl unit differences of five and six are the most stable. In complexes featuring the same size difference, the complex stabilities slightly increase with an increasing size of the involved [n]CPPs. Utilizing the π-extended [12]carbon nanobelt ([12]CNB) as the guest also revealed an increase in complex stability. This study paves the way for a deeper understanding of the host-guest chemistry of CPPs.

The attachment of silver(i) cations to 5,7,12,14-tetraphenyl-6,13-diazapentacene and its reduced dihydro-form has been studied by electrospray ionization mass spectrometry (ESI-MS). The structure elucidation of the Ag+ complexes has been accomplished in gas-phase collision experiments in conjunction with density functional theory (DFT) calculations. The oxidized form provides a favourable cavity for the Ag+ ion, leading to the [1 : 1] complex with the highest resilience towards dissociation and severely hindering the attainment of a second molecular ligand. When the nitrogen is hydrogenated in the reduced dihydro-form, the cavity is partly blocked. This leads to a less strongly bound [1 : 1] complex ion but facilitates the attachment of a second molecular ligand to the Ag+. The resulting complex is the most stable among the [2 : 1] complexes. DFT calculations provide valuable insight into the geometries of the complex ions. Adding silver(i) to the reduced dihydro-form for cationization also induces its oxidation in solution. The oxidative dehydrogenation reaction, for which a mechanism is proposed, proceeds by first order kinetics and is markedly accelerated by day light.

In this work, we compare for the first time the stability of [n]cycloparaphenylene ([n]CPP)-based host-guest complexes with Li+@C60 and C60 in the gas and the solution phase. Our gas-phase experiments reveal a significant increase in stability for the complexes featuring [9-12]CPP with Li+@C60. This increased interaction strength is also observed in solution. Isothermal titration calorimetry shows for the formation of [10]CPP⊃Li+@C60 a two orders of magnitude larger association constant than that for the C60 analog. Additionally, an increased binding entropy is observed. This study contributes to a better understanding of host-guest complexes between [n]CPPs and endohedral metallofullerenes at a molecular level, which is the prerequisite for future applications.

Carbon nanodots (CNDs) synthesized from citric acid and formyl derivatives, that is, formamide, urea, or N-methylformamide, stand out through their broad-range visible-light absorbance and extraordinary photostability. Despite their potential, their use has thus far been limited to imaging research. This work has now investigated the link between CNDs' photochemical properties and their chemical structure. Electron-rich, yellow carbon nanodots (yCNDs) are obtained with in situ addition of NaOH during the synthesis, whereas otherwise electron-poor, red carbon nanodots (rCNDs) are obtained. These properties originate from the reduced and oxidized dimer of citrazinic acid within the matrix of yCNDs and rCNDs, respectively. Remarkably, yCNDs deposited on TiO2 give a 30% higher photocurrent density of 0.7 mA cm-2 at +0.3 V versus Ag/AgCl under Xe-lamp irradiation (450 nm long-pass filter, 100 mW cm-2 ) than rCNDs. The difference in overall photoelectric performance is due to fundamentally different charge-transfer mechanisms. These depend on either the electron-accepting or the electron-donating nature of the CNDs, as is evident from photoelectrochemical tests with TiO2 and NiO and time-resolved spectroscopic measurements.

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.

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.