Markus Freiberger’s research while affiliated with Friedrich-Alexander-University of Erlangen-Nürnberg and other places

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.

[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...

[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 charge transfer allowed the observation of energy transfer from the porphyrin triplet to the fullerene triplet state with a lifetime of ca. 25 ms. 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.

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.

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).