Fluorophores are powerful tools for interrogating biological systems. Carbon nanotubes (CNTs) have long been attractive materials for biological imaging due to their nearinfrared excitation and bright, tunable optical properties. The difficulty in synthesizing and functionalizing these materials with precision, however, has hampered progress in this area. Carbon nanohoops, which are macrocyclic CNT substructures, are carbon nanostructures that possess ideal photophysical characteristics of nanomaterials, while maintaining the precise synthesis of small molecules. However, much work remains to advance the nanohoop class of fluorophores as biological imaging agents. Herein, we report an intracellular targeted nanohoop. This fluorescent nanostructure is noncytotoxic at concentrations up to 50 μM, and cellular uptake investigations indicate internalization through endocytic pathways. Additionally, we employ this nanohoop for two-photon fluorescence imaging, demonstrating a high two-photon absorption cross-section (65 GM) and photostability comparable to a commercial probe. This work further motivates continued investigations into carbon nanohoop photophysics and their biological imaging applications.

New strategies for synthesizing polyyne polyrotaxanes are being developed as an approach to stable carbyne “insulated molecular wires”. Here we report an active metal template route to polyyne [3]rotaxanes, using dicobalt carbonyl masked alkyne equivalents. We synthesized two [3]rotaxanes, both with the same C28 polyyne dumbbell component, one with a phenanthroline‐based macrocycle and one using a 2,6‐pyridyl cycloparaphenylene nanohoop. The thermal stabilities of the two rotaxanes were compared with that of the naked polyyne dumbbell in decalin at 80 °C, and the nanohoop rotaxane was found to be 4.5 times more stable.

Hydrogen sulfide (H 2 S) is a biologically relevant molecule, and recent efforts have focused on developing small molecular donors that deliver H 2 S on demand. Acid-activated donors have garnered significant interest due to the potential application of such systems in myocardial ischemia injury or for suppressing tumor growth. In this work, we report a new strategy for tuning H 2 S delivery to a specific pH window. Specifically, we utilize self-immolative thiocarbamates with an imine-derived triggering group. After imine hydrolysis, the self-immolative decomposition releases carbonyl sulfide (COS), which is quickly hydrolyzed to H 2 S by carbonic anhydrase. Although acid-mediated hydrolysis results in imine cleavage, environments that are too acidic result in protonation of the aniline intermediate and results in inhibition of COS/H 2 S release. Taken together, this mechanism enables access to donor motifs that are only activated within specific pH windows. Here, we demonstrate the design, preparation, and pH evaluation of a series of imine-based COS/H 2 S donor motifs, which we anticipate that will have utility in investigating H 2 S in acidic microenvironments.

A novel fluorescent probe design based on the interlocking of a reactive thread in a rigid nanohoop fluorophore is reported. This rotaxane design leads to size-selective sensing of thiolates in organic solution.More broadly, the work suggests the promise of mechanical interlocking to enhance the selectivity of reaction-based probes. File list (2)download file view on ChemRxiv H2S_rotaxane_preprint.pdf (0.93 MiB) download file view on ChemRxiv H2S_rotaxane_SI.pdf (1.47 MiB)