Light induced fullerene dimerization is controlled by both the fullerene and polymer morphology of organic solar cells.

Although chemists have made small-molecule rotary motors, to date there have been no reports of small-molecule linear motors. Here we describe the synthesis and operation of a 21-atom two-legged molecular unit that is able to walk up and down a four-foothold molecular track. High processivity is conferred by designing the track-binding interactions of the two feet to be labile under different sets of conditions such that each foot can act as a temporarily fixed pivot for the other. The walker randomly and processively takes zero or one step along the track using a 'passing-leg' gait each time the environment is switched between acid and base. Replacing the basic step with a redox-mediated, disulfide-exchange reaction directionally transports the bipedal molecules away from the minimum-energy distribution by a Brownian ratchet mechanism. The ultimate goal of such studies is to produce artificial, linear molecular motors that move directionally along polymeric tracks to transport cargoes and perform tasks in a manner reminiscent of biological motor proteins.

Movement is intrinsic to life. Biologists have established that most forms of directed nanoscopic, microscopic and, ultimately, macroscopic movements are powered by molecular motors from the dynein, myosin and kinesin superfamilies. These motor proteins literally walk, step by step, along polymeric filaments, carrying out essential tasks such as organelle transport. In the last few years biological molecular walkers have inspired the development of artificial systems that mimic aspects of their dynamics. Several DNA-based molecular walkers have been synthesised and shown to walk directionally along a track upon sequential addition of appropriate chemical fuels. In other studies, autonomous operation--i.e. DNA-walker migration that continues as long as a complex DNA fuel is present--has been demonstrated and sophisticated tasks performed, such as moving gold nanoparticles from place-to-place and assistance in sequential chemical synthesis. Small-molecule systems, an order of magnitude smaller in each dimension and 1000× smaller in molecular weight than biological motor proteins or the walker systems constructed from DNA, have also been designed and operated such that molecular fragments can be progressively transported directionally along short molecular tracks. The small-molecule systems can be powered by light or chemical fuels. In this critical review the biological motor proteins from the kinesin, myosin and dynein families are analysed as systems from which the designers of synthetic systems can learn, ratchet concepts for transporting Brownian substrates are discussed as the mechanisms by which molecular motors need to operate, and the progress made with synthetic DNA and small-molecule walker systems reviewed (142 references).

Since 1996, a growing number of strained macrocycles, comprising only sp2‐ or sp‐hybridized carbon atoms within the ring, have become synthetically accessible, with the [n]cycloparaphenyleneacetylenes (CPPAs) and the [n]cycloparaphenylenes (CPPs) being the most prominent examples. Now that robust and relatively general synthetic routes toward a diverse range of nanohoop structures have become available, the research focus is beginning to shift towards the exploration of their properties and applications. From a supramolecular chemistry perspective, these macrocycles offer unique opportunities as a result of their near‐perfect circular shape, the unusually high degree of shape‐persistence, and the presence of both convex and concave π‐faces. In this Minireview, we give an overview on the use of strained carbon‐rich nanohoops in host–guest chemistry, the preparation of mechanically interlocked architectures, and crystal engineering.

The cycloparaphenylenes (CPPs) are a class of strained macrocycles that until 2008 were considered beyond the reach of organic synthesis. With its cyclic array of ten para-substituted phenylene rings, [10]­CPP possesses a concave π-system that is perfectly preorganized for the strong supramolecular association of convex fullerenes such as C60. Although mechanically interlocked CPP architectures have been observed in the gas phase, the rational synthesis of bulk quantities has not been achieved yet, which is likely due to the fact that conventional template strategies are not amenable to CPP rings that lack heteroatoms. Here, we report the synthesis of two [2]­rotaxanes in which a [10]­CPP ring binds to a central fullerene bis-adduct and is prevented from dethreading by the presence of two bulky fullerene hexakis-adduct stoppers. The final step in the rotaxane synthesis is surprisingly efficient (up to ca. 40% yield) and regioselective because the fullerene acts as an efficient convex template, while [10]­CPP acts as a supramolecular directing group, steering the reaction at the central fullerene exclusively toward two trans regioisomers. Comprehensive physicochemical studies confirmed the interlocked structure, shed light on the dynamic nature of the CPP–fullerene interaction, and revealed intriguing consequences of the mechanical bond on charge transfer processes. In light of recent advances in the synthesis of nanohoops and nanobelts, our concave–convex π–π templating strategy may be broadly useful and enable applications in molecular electronics or complex molecular machinery.

Efficient photoinduced electron transfer was observed across a [10]cycloparaphenylene ([10]CPP) moiety that serves as a rigid non-covalent bridge between a zinc porphyrin and a range of fullerenes. The preparation of iodo-[10]CPP is the key to the synthesis of a porphyrin-[10]CPP conjugate, which binds C , C , (C ) , and other fullerenes (K >10 m ). Fluorescence and pump-probe spectroscopy revealed intramolecular energy transfer between CPP and porphyrin and also efficient charge separation between porphyrin and fullerenes, affording up to 0.5 μs lifetime charge-separated states. The advantage of this approach towards electron donor-acceptor dyads is evident in the case of dumbbell-shaped (C ) , which gave intricate charge-transfer behavior in 1:1 and 2:1 complexes. These results suggest that [10]CPP and its cross-coupled derivatives could act as supramolecular mediators of charge transport in organic electronic devices.

Walk this way! A walker unit is able to walk in either direction along a four‐foothold molecular track, depending on the sequence of application of four external stimuli: acid, base, UV light, and visible light in the presence of iodine (see picture). The isomerization of the stilbene moiety in the molecular track is key for the achievement of directional transport through a Brownian ratchet mechanism.

The discovery of coronands and cryptands, organic compounds that can accommodate metal ions in a preorganized two- or three-dimensional environment, was a milestone in supramolecular chemistry, leading to countless applications from organic synthesis to metallurgy and medicine. These compounds are typically prepared via multistep organic synthesis and one of their characteristic features is the high stability of their covalent framework. Here we report the use of a dynamic covalent exchange reaction for the one-pot template synthesis of a new class of coronates and cryptates, in which acid-labile O,O,O-orthoesters serve as bridgeheads. In contrast to their classic analogues, the compounds described herein are constitutionally dynamic in the presence of acid and can be induced to release their guest via irreversible deconstruction of the cage. These properties open up a wide range of application opportunities, from systems chemistry to molecular sensing and drug delivery.