A Neutral Naphthalene Diimide [2]Rotaxane

Self-Healing of a Copper(I) [2]Rotaxane Shuttle Monitored by Fluorescence

We demonstrate self-healing of the shuttling dynamics of a molecular machine operating by negative feedback. When zinc(II) was added to the copper(I)-loaded [2]rotaxane shuttle [Cu(R)]⁺, copper(I) was replaced, thereby generating the static zinc(II)-loaded [2]rotaxane [Zn(R)]²⁺. Loss of the dynamics was accompanied by a fluorescence enhancement at λ = 364 nm. Notably, the released copper(I) ions catalyzed the formation of a bis-triazole ligand, which selectively captured zinc(II). As a result, the copper(I) was restored in the rotaxane, and the dynamic shuttling motion of [Cu(R)]⁺ was regained. The healing was conveniently followed by diagnostic fluorescence changes.

Force-Induced Shuttling of Rotaxanes Controls Fluorescence Resonance Energy Transfer in Polymer Hydrogels

The molecular shuttling function of rotaxanes can be exploited to design mechanoresponsive reporter molecules. Here, we report a new approach to such rotaxane-based mechanophores, in which the fluorescence resonance energy transfer (FRET) between a donor-acceptor pair is mechanically controlled. A cyclic molecule containing a green-light-emitting FRET donor connected to a red-light-emitting FRET acceptor was threaded onto an axle equipped with a quencher at its center and two stoppers in the peripheral positions. In the force-free state, the green emitter is located near the quencher so that charge transfer interactions or photo-induced electron transfer between the two moieties suppress green emission and prevent the FRET from the green to the red emitter. The mechanophore was covalently incorporated into a linear polyurethane-urea (PUU), and stretchable hydrogels were prepared by swelling this polymer with water. Upon deformation of the PUU hydrogels and under an excitation light that selectively excites the donor, the intensity of the red fluorescence increases, as a result of a force-induced separation of the green emitter from the quencher, which enables the FRET. The switching contrast is much more pronounced in the gels than in dry films, which is due to increased molecular mobility and hydrophobic effects in the hydrogel, which both promote the formation of inclusion complexes between the ring containing the green emitter and the quencher.

Nano-Theranostics for the Sensing, Imaging and Therapy of Prostate Cancers

We highlight hereby recent developments in the emerging field of theranostics, which encompasses the combination of therapeutics and diagnostics in a single entity aimed for an early-stage diagnosis, image-guided therapy as well as evaluation of therapeutic outcomes of relevance to prostate cancer (PCa). Prostate cancer is one of the most common malignancies in men and a frequent cause of male cancer death. As such, this overview is concerned with recent developments in imaging and sensing of relevance to prostate cancer diagnosis and therapeutic monitoring. A major advantage for the effective treatment of PCa is an early diagnosis that would provide information for an appropriate treatment. Several imaging techniques are being developed to diagnose and monitor different stages of cancer in general, and patient stratification is particularly relevant for PCa. Hybrid imaging techniques applicable for diagnosis combine complementary structural and morphological information to enhance resolution and sensitivity of imaging. The focus of this review is to sum up some of the most recent advances in the nanotechnological approaches to the sensing and treatment of prostate cancer (PCa). Targeted imaging using nanoparticles, radiotracers and biomarkers could result to a more specialised and personalised diagnosis and treatment of PCa. A myriad of reports has been published literature proposing methods to detect and treat PCa using nanoparticles but the number of techniques approved for clinical use is relatively small. Another facet of this report is on reviewing aspects of the role of functional nanoparticles in multimodality imaging therapy considering recent developments in simultaneous PET-MRI (Positron Emission Tomography-Magnetic Resonance Imaging) coupled with optical imaging in vitro and in vivo, whilst highlighting feasible case studies that hold promise for the next generation of dual modality medical imaging of PCa. It is envisaged that progress in the field of imaging and sensing domains, taken together, could benefit from the biomedical implementation of new synthetic platforms such as metal complexes and functional materials supported on organic molecular species, which can be conjugated to targeting biomolecules and encompass adaptable and versatile molecular architectures. Furthermore, we include hereby an overview of aspects of biosensing methods aimed to tackle PCa: prostate biomarkers such as Prostate Specific Antigen (PSA) have been incorporated into synthetic platforms and explored in the context of sensing and imaging applications in preclinical investigations for the early detection of PCa. Finally, some of the societal concerns around nanotechnology being used for the detection of PCa are considered and addressed together with the concerns about the toxicity of nanoparticles–these were aspects of recent lively debates that currently hamper the clinical advancements of nano-theranostics. The publications survey conducted for this review includes, to the best of our knowledge, some of the most recent relevant literature examples from the state-of-the-art. Highlighting these advances would be of interest to the biomedical research community aiming to advance the application of theranostics particularly in PCa diagnosis and treatment, but also to those interested in the development of new probes and methodologies for the simultaneous imaging and therapy monitoring employed for PCa targeting.

Subphthalocyanine-Stoppered [2]Rotaxanes: Synthesis and Size/Energy Threshold of Slippage

Subphthalocyanine (SubPc)-stoppered [2]rotaxanes were synthesized for the first time. The rotaxane bearing unsubstituted SubPc as a stopper exhibited an equilibrium of slipping-on and slipping-off, whereas a perfluorinated SubPc stopper completely blocked slippage of the ring due to its slightly larger size. Kinetic studies revealed the Gibbs free energy of activation for the slipping-on and slipping-off processes. The optical properties of the rotaxanes, including photoinduced electron transfer, were also revealed.

Mechanoresponsive Behavior of a Polymer-Embedded Red-Light Emitting Rotaxane Mechanophore

A red light-emitting photoluminescent supramolecular mechanophore based on an interlocked molecular motif is presented. The rotaxane-based mechanophore contains a cyclic compound featuring a π-extended 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye as a red emitter that was threaded onto a dumbbell-shaped molecule containing an electron-poor 1,4,5,8-naphthalenetetracarboxylic diimide quencher at its center. Through two aliphatic hydroxyl groups attached to the dumbbell and the cycle, the mechanophore was covalently embedded into the backbone of a thermoplastic polyurethane elastomer. The mechanophore is only weakly photoluminescent in solution, indicating that the BODIPY's emission is efficiently quenched. Solution-cast films of the rotaxane-containing polymer, by contrast, show an appreciable photoluminescence, which suggests that during film formation, some of the emitting cycles are trapped in positions away from the quencher. Interestingly, the emission intensity could be significantly reduced by swelling the films with an organic solvent and the emission increased again upon drying, suggesting that such solvent plasticization causes a reversible rearrangement. In both dry and solvent-swollen films, uniaxial deformation caused a significant, reversible increase of the emission intensity, on account of mechanically induced shuttling of the emitters away from and back to the quenchers. It is shown that the properties of the polymer can be tuned by the solvent, and that such plasticizing extends the small palette of approaches that allow modification of the activation stress of a given material system.

Rotaxane-Based Mechanophores Enable Polymers with Mechanically Switchable White Photoluminescence

Three mechanoresponsive polyurethane elastomers whose blue, green, and orange photoluminescence can be reversibly turned on by mechanical force were prepared and combined to create a blend that exhibits deformation-induced white photoluminescence. The three polyurethanes contain rotaxane-based supramolecular mechanoluminophores based on π-extended pyrene, anthracene, or 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) luminophores, respectively, and 1,4,5,8-naphthalenetetracarboxylic diimide as an electronically matched quencher. Each polymer shows instantly reversible, strain-dependent switching of its photoluminescence intensity when stretched and relaxed, as deformation leads to a spatial separation of the luminophore and quencher. The present study shows that the photoluminescence color can easily be tailored by variation of the luminophore and also by combining several mechanophores in one material and demonstrates that adaptability is a key advantage of supramolecular approaches to create mechanoresponsive polymers.

[2]Rotaxane End-Capping Synthesis by Click Michael-Type Addition to the Vinyl Sulfonyl Group

We report the application of the click Michael-type addition reaction to vinyl sulfone or vinyl sulfonate groups in the synthesis of rotaxanes through the threading-and-capping method. This methodology has proven to be efficient and versatile as it allowed the preparation of rotaxanes using template approaches based on different noncovalent interactions (i.e., donor-acceptor π-π interactions or hydrogen bonding) in yields of generally 60-80 % and up to 91 % aided by the mild conditions required (room temperature or 0 °C and a mild base such as Et₃ N or 4-(N,N-dimethylamino)pyridine (DMAP)). Furthermore, the use of vinyl sulfonate moieties, which are suitable motifs for coupling-and-decoupling (CAD) chemistry, implies another advantage because it allows the controlled chemical disassembly of the rotaxanes into their components through nucleophilic substitution of the sulfonates resulting from the capping step with a thiol under mild conditions (Cs₂ CO₃ and room temperature).

Rotaxanes as Mechanochromic Fluorescent Force Transducers in Polymers

The integration of mechanophores, motifs that transduce mechanical forces into chemical reactions, allows creating materials with stress-dependent properties. Typical mechanophores are activated by cleaving weak covalent bonds, but these reactions can also be triggered by other stimuli, and this renders the behavior unspecific. Here we show that this problem can be overcome by extending the molecular-shuttle function of rotaxanes to mechanical activation. A mechanically interlocked mechanophore composed of a fluorophore-carrying macrocycle and a dumbbell-shaped molecule containing a matching quencher was integrated into a polyurethane elastomer. Deformation of this polymer causes a fluorescence turn-on, due to the spatial separation of fluorophore and quencher. This process is specific, efficient, instantly reversible, and elicits an easily detectable optical signal that correlates with the applied force.

Synthesis and Photoisomerization of Substituted Dibenzofulvene Molecular Rotors

The synthesis, spectral and structural characterization, and photoisomerization of a family of 2-substituted dibenzofulvene molecular actuators based on (2,2,2-triphenylethylidene)fluorene (TEF) are reported. The 2-substituted species investigated are nitro (NTEF), cyano (CTEF), and iodo (ITEF). X-ray structures of these three compounds and three intermediates were determined to assign alkene configuration and investigate the effects of the 2-substituents on steric gearing. The addition-elimination reaction of Z-9 with trityl anion to form Z-10 proceeded with complete retention of configuration. Rates of photoisomerization were measured at irradiation wavelengths between 266-355 nm in acetonitrile/dioxane solutions at room temperature. Photoisomerization quantum yields (φ) were calculated by means of a mathematical model that accounts for a certain degree of photodecomposition in the cases of CTEF and ITEF. Quantum yields vary significantly with substituent, having maximum values of φ=0.26 for NTEF, 0.39 for CTEF, and 0.50 for ITEF. NTEF is photochemically robust and has a large quantum yield for photoisomerization in the near-UV, making it a particularly promising drive rotor moiety for light-powered molecular devices.

A redox-controllable molecular switch based on weak recognition of BPX26C6 at a diphenylurea station

The Na⁺ ion–assisted recognition of urea derivatives by BPX26C6 has allowed the construction of a redox-controllable [2]rotaxane-type molecular switch based on two originally very weakly interacting host/guest systems. Using NOBF₄ to oxidize the triarylamine terminus into a corresponding radical cation attracted the macrocyclic component toward its adjacent carbamate station; subsequent addition of Zn powder moved the macrocyclic component back to its urea station.

Tailor-made design of J- or H-aggregated naphthalenediimide-based gels and remarkable fluorescence turn on/off behaviour depending on solvents

Design of a supramolecular chameleon that displays solvent dependent control over H/J-aggregation as well as fluorescence turn on/off behaviour depending on the proper choice of solvents.

Direct core functionalisation of naphthalenediimides by iridium catalysed C–H borylation

We report the first boron-substituted naphthalenediimides (NDIs), prepared by iridium catalysed C–H activation. Both mono- and diborylated products are available, which have been further elaborated by Suzuki–Miyaura coupling.

Interaction between monomers of two surfactants derived from the [Ru(2,2'-bpy)(3)](2+) complex and α, β and γ-cyclodextrins: formation of [2]- and [3]-pseudorotaxanes

Two new surfactants derived from the tris(2,2'-bipyridine) ruthenium(II) complex, [Ru(2,2'-bpy)(3)](2+), were synthesized and characterized: the double-tailed [Ru(2,2'-bipy)2(4,4'-(C(11)H(23))(2)-2,2'-bipy)](2+) surfactant (RuC11) and the mono-tailed [Ru(2,2'-bipy)(2)(4-(CH(3))-4'-(C(13)H(27))-2,2'-bipy)](2+) surfactant (RuC13). The main characteristic of these species is the presence of an inorganic complex as the polar head of the surfactant with interesting luminescence properties, which were used to study the interaction of these cationic surfactants with α-, β- and γ-cyclodextrins (CD). The results showed the formation of [2]- and [3]-pseudorotaxanes. The binding constant values as well as the stoichiometry of the complexes formed were obtained; the results were confirmed, from a qualitative point of view, with NMR spectra.