A Fluorescent, Shape-Persistent Dendritic Host with Photoswitchable Guest Encapsulation and Intramolecular Energy Transfer

Thermally Stable Photomechanical Molecular Hinge: Sterically Hindered Stiff-Stilbene Photoswitch Mechanically Isomerizes

Molecular photoswitches are extensively used as molecular machines because of the small structures, simple motions, and advantages of light including high spatiotemporal resolution. Applications of photoswitches depend on the mechanical responses, in other words, whether they can generate motions against mechanical forces as actuators or can be activated and controlled by mechanical forces as mechanophores. Sterically hindered stiff stilbene (HSS) is a promising photoswitch offering large hinge-like motions in the E/Z isomerization, high thermal stability of the Z isomer, which is relatively unstable compared to the E isomer, with a half-life of ca. 1000 years at room temperature, and near-quantitative two-way photoisomerization. However, its mechanical response is entirely unexplored. Here, we elucidate the mechanochemical reactivity of HSS by incorporating one Z or E isomer into the center of polymer chains, ultrasonicating the polymer solutions, and stretching the polymer films to apply elongational forces to the embedded HSS. The present study demonstrated that HSS mechanically isomerizes only in the Z to E direction and reversibly isomerizes in combination with UV light, i.e., works as a photomechanical hinge. The photomechanically inducible but thermally irreversible hinge-like motions render HSS unique and promise unconventional applications differently from existing photoswitches, mechanophores, and hinges.

Synthesis of a Series of 12-Membered Azobenzene Macrocycles and Tuning of the Half-Life of the Thermal Z-E Isomerization

Azobenzene macrocycles (AzMs) represent a class of azobenzene that are typically photoswitchable with good switching yields of E and Z isomers at certain photostationary states. Here, the synthesis and versatile functionalization of 12-membered AzMs is presented to obtain various meta- and para-aryl-substituted AzMs in high yields of 71-98%. At different positions in the periphery, these substituents significantly impact on the thermal half-lives of the less-stable Z isomers. Para-substitution leads to faster thermal relaxation than meta-substitution, and electron-donating groups lead to a faster relaxation than electron-withdrawing groups.

Review of photoresponsive and glycoside dendrimers in biomaterials and sensors applications

Dendrimers are branched molecules with well-defined lengths, shapes, molecular weights, and monodispersity in comparison to linear polymers.

Differences in thermal expansion and motion ability for herringbone and face-to-face π-stacked solids

A series of aromatic organic molecules functionalized with different halogen atoms (I/ Br), motion-capable groups (olefin, azo or imine) and molecular length were designed and synthesized. The molecules self-assemble in the solid state through halogen bonding and exhibit molecular packing sustained by either herringbone or face-to-face π-stacking, two common motifs in organic semiconductor molecules. Interestingly, dynamic pedal motion is only achieved in solids with herringbone packing. On average, solids with herringbone packing exhibit larger thermal expansion within the halogen-bonded sheets due to motion occurrence and molecular twisting, whereas molecules with face-to-face π-stacking do not undergo motion or twisting. Thermal expansion along the π-stacked direction is surprisingly similar, but slightly larger for the face-to-face π-stacked solids due to larger changes in π-stacking distances with temperature changes. The results speak to the importance of crystal packing and intermolecular interaction strength when designing aromatic-based solids for organic electronics applications.

Dendritic polyphenylene AIEgens: fluorescence detection of explosives and stimulus-responsive luminescence

Dendritic AIEgens with polyphenylene peripherals and TPE luminescent core had shown detection capability to picric acid and tunable response to external stimulus.

Multi-stimuli programmable FRET based RGB absorbing antennae towards ratiometric temperature, pH and multiple metal ion sensing

A red-green-blue (RGB) multichromophoric antenna 1 consisting of energy donors naphthalimides and perylenediimides and a central aza-BODIPY energy acceptor along with two subchromophoric red-blue (RB 6) and green-blue (GB 12) antennae was designed that showed efficient cascade Förster resonance energy transfer (FRET). RGB antenna 1 showed pronounced temperature-dependent emission behaviour where emission intensities in green and red channels could be tuned in opposite directions by temperature giving rise to unique ratiometric sensing with a temperature sensitivity of 0.4% °C. RGB antenna 1 showed reversible absorption modulation selectively in the blue region (RGB ↔ RG) upon acid/base addition giving rise to pH sensing behaviour. Furthermore, RGB antenna 1 was utilized to selectively sense metal ions such as Co2+ and Fe3+ through a FRET turn-off mechanism induced by a redox process at the aza-BODIPY site that resulted in the selective spectral modulation of the red band (i.e., RGB → GB). Model antenna RB 6 showed white light emission with chromaticity coordinates (0.32, 0.33) on acid addition. Antennae 1, 6 and 12 also exhibited solution state electrochromic switching characterized by distinct colour changes upon changing the potential. Finally, antennae 1, 6 and 12 served as reversible fluorescent inks in PMMA/antenna blends whereby the emission colours could be switched or tuned using different stimuli such as acid vapour, temperature and metal ions.

Giant Shape-Persistent Tetrahedral Porphyrin System: Light-Induced Charge Separation

Tetraphenylmethane appended with four pyridylpyridinium units works as a scaffold to self‐assemble four ruthenium porphyrins in a tetrahedral shape‐persistent giant architecture. The resulting supramolecular structure has been characterised in the solid state by X‐ray single crystal analysis and in solution by various techniques. Multinuclear NMR spectroscopy confirms the 1 : 4 stoichiometry with the formation of a highly symmetric structure. The self‐assembly process can be monitored by changes of the redox potentials, as well as by modifications in the visible absorption spectrum of the ruthenium porphyrin and by a complete quenching of both the bright fluorescence of the tetracationic scaffold and the weak phosphorescence of the ruthenium porphyrin. An ultrafast photoinduced electron transfer is responsible for this quenching process. The lifetime of the resulting charge separated state (800 ps) is about four times longer in the giant supramolecular structure compared to the model 1 : 1 complex formed by the ruthenium porphyrin and a single pyridylpyridinium unit. Electron delocalization over the tetrameric pyridinium structure is likely to be responsible for this effect.

Visible-Light Responsive Sucrose-Containing Macrocyclic Host for Cations

Chiral photoresponsive host 1 was prepared by a high-yield Cs₂CO₃-templated macrocyclization. Trans-1 transforms into long-lived cis-1 (25 days) upon irradiation with green light, and the backward transformation is triggered by blue light. Both isomers prefer potassium among alkali metal cations, and cis-1 binds cations stronger than trans-1 (K_cis/K_trans ≤ 4.1). ¹H NMR titration experiments as well as density functional theory studies reveal that sucrose ring oxygen residues and azobenzene nitrogen atoms in 1 contribute to cation coordination.

Wavelength-Selective Light-Controlled Stepwise Photolysis from Single Gold Nanoparticles

Light-controlled sequential photolysis from a single nanoparticle is a challenge for controlled release. A wavelength-selective sequential photolysis from single gold nanoparticles is reported for the first time. In particular, it is also demonstrated that such nanoparticle can be used to sequentially release two payloads in living cells. In principle, this system can be extended to sequential release of multiple different types of payloads by rational design of diverse photocleavable linkers. It is expected that this work can provide a new tool for better orderly controlling cellular events that request high spatiotemporal manners.

Reversible fluorescence modulation through the photoisomerization of an azobenzene-bridged perylene bisimide cyclophane

An azobenzene-bridged perylene bisimide cyclophane was designed and synthesized, which showed reversible fluorescence intensity switching under light-irradiation due to cooperative adjustments of PBI–PBI and PBI–Azo interactions.

Rational design and facile fabrication of biocompatible triple responsive dendrimeric nanocages for targeted drug delivery

Multi-responsive polymeric nanoparticles have shown great promise in the sufficient site-specific delivery of drugs in heterogeneous and complicated biological microenvironments, but without great success due to many problems such as sophisticated manufacture process, high cost and cytotoxicity. In this work, a novel triple responsive dendrimeric nanocage (TDN) is fabricated through co-assembling and cross-linking of lipoic acid modified low generation dendrimers with lipoic acid modified polyethylene glycols (PEGs). This nanocage exhibits improved drug loading capacity (about 2 times higher) at a lower temperature and stimuli-responsive drug release profile upon the stimulation of temperature, acid pH and reducing agent. More importantly, the nanocage promotes drug internalization, conduces endosomal escape, and realizes intracellular controlled drug release. Furthermore, the nanocage significantly improves the pharmacokinetics and biodistribution of antitumor drugs, confirming the potent in vivo therapeutic effect with reduced side effects. The rational design and facile fabrication of multi-responsive dendrimeric nanocages provide a "proof-of-concept" for precise targeted drug delivery, and may have great potential for clinical use in the future.

Synthesis and Photocontrolled Supramolecular Self-Assembly of Azobenzene-Functionalized Perylene Bisimide Derivatives

Azobenzene (Azo) units were successfully introduced into perylene bisimide (PBI) structures in order to realize the photocontrolling of the morphology of the supramolecular assembly of PBI by a photoisomerization process. A total of three Azo-functionalized perylene bisimide derivatives (PBI1, PBI2, and PBI3) with different alkyl chain lengths were designed and synthesized by imidization of 3,4,9,10-perylene tetracarboxylic dianhydride with the corresponding amines. The structures of these compounds were characterized by proton nuclear magnetic resonance (¹H NMR) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The photoisomerization behaviors of Azo units in PBIs were investigated using ultraviolet-visible (UV-VIS) absorption spectroscopy, which were obviously effected by solvents and the alkyl chain length. Furthermore, the photoisomerization of Azo units has the obviously regulatory effect on the morphology of supramolecular assembly of PBIs, especially for the medium-length alkyl chain-linked Azo-functionalized PBI derivative (PBI2). This research realized the photocontrolling of the morphology of the supramolecular assembly of PBI derivatives by photoisomerization of Azo units.

Design and synthesis of a fluorescent amino poly(glycidyl methacrylate) for efficient gene delivery

A fluorescent amino poly(glycidyl methacrylate) (PGOHMA) was synthesized by atom transfer radical polymerization (ATRP) and post-polymerization. PGOHMA has low cytotoxicity and high DNA delivery efficiency.

Nitrosopyridine Probe To Detect Polyketide Natural Products with Conjugated Alkenes: Discovery of Novodaryamide and Nocarditriene

An optimized nitroso-based probe that facilitates the discovery of conjugated alkene-containing natural products in unprocessed extracts was developed. It chemoselectively reacts with conjugated olefins via a nitroso-Diels-Alder cyclization to yield derivatives with a distinct chromophore and an isotopically unique bromine atom that can be rapidly identified using liquid chromatography/mass spectrometry and a bioinformatics tool called MeHaloCoA (Marine Halogenated Compound Analysis). The probe is ideally employed when genome-mining techniques identify strains containing polyketide gene clusters with two or more repeating KS-AT-DH-KR-ACP domain sequences, which are required for the biosynthesis of conjugated alkenes. Comparing the reactivity and spectral properties of five brominated arylnitroso reagents with model compounds spiramycin, bufalin, rapamycin, and rifampicin led to the identification of 5-bromo-2-nitrosopyridine as the most suitable probe structure. The utility of the dienophile probe was then demonstrated in bacterial extracts. Tylactone, novodaryamide and daryamide A, piperazimycin A, and the saccharamonopyrones A and B were cleanly labeled in extracts from their respective bacterial producers, in high regioselectivity but with varying degrees of diastereoselectivity. Further application of the method led to the discovery of a new natural product called nocarditriene, containing an unprecedented epoxy-2,3,4,5-tetrahydropyridine structure, from marine-derived Nocardiopsis strain CNY-503.

Expanding the limits of synthetic macromolecular chemistry through Polyphenylene Dendrimers

Polyphenylene dendrimers (PPDs) are a unique class of macromolecules because their backbone is made from twisted benzene repeat units that result in a rigid, shape-persistent architecture as reported by Hammer et al. (Chem Soc Rev 44:4072-4090, 2015) and Hammer and Müllen (Chem Rev 116:2103-210, 2016) These dendrimers can be synthetically tailored at their core, scaffold, and surface to introduce a wide range of chemical functionalities that influence their applications. It is the balance between the macromolecular properties of polyphenylene dendrimers with grandiose synthetic ingenuity that presents a template for the next generation of synthetic dendrimers to achieve complex structures other chemistry fields cannot. This perspective will look at how advances in synthetic chemistry have led to an explosion in the properties of polyphenylene dendrimers from their initial stage, as PPDs that were used as precursors for nanographenes, to next-generation dendrimers for organic electronic devices, sensors for volatile organic compounds (VOCs), nanocarriers for small molecules, and even as complexes with therapeutic drugs and viruses, among others. Ideally, this perspective will illustrate how the evolution of synthetic chemistry has influenced the possible structures and properties of PPDs and how these chemical modifications have opened the door to unprecedented applications.

Ligand-Binding Ability of a Porphyrin Core in a Dendrimer with Rigid Branched Terminal Components

A dendrimer with rigid branched terminal components was prepared by a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction. A zinc 5,15-diethynyl-10,20-bis(3,5-di- tert-butylphenyl)porphyrin unit was incorporated at the core of the dendrimer as a receptor site for an added pyridyl ligand. The appearance of an absorption band characteristic of the planar conformer of conjugated chains in the terminal components suggested that the dendrimer adopts a folded higher order structure in dichloromethane at 25 °C. The binding constant between the zinc porphyrin core and a pyridyl ligand was evaluated by means of UV-vis absorption titration and compared with that of a suitable reference compound. The incorporation of the zinc porphyrin core into the folded dendrimer led to considerable suppression of its ligand-binding ability.

Light-responsive molecular containers

This review highlights relevant studies of light-controlled molecular containers able to catch and release small molecules.

Coupling carbon nanomaterials with photochromic molecules for the generation of optically responsive materials

Multifunctional carbon-based nanomaterials offer routes towards the realization of smart and high-performing (opto)electronic (nano)devices, sensors and logic gates. Meanwhile photochromic molecules exhibit reversible transformation between two forms, induced by the absorption of electromagnetic radiation. By combining carbon-based nanomaterials with photochromic molecules, one can achieve reversible changes in geometrical structure, electronic properties and nanoscale mechanics triggering by light. This thus enables a reversible modulation of numerous physical and chemical properties of the carbon-based nanomaterials towards the fabrication of cognitive devices. This review examines the state of the art with respect to these responsive materials, and seeks to identify future directions for investigation.

Azobenzenes and catalysis

Azobenzene is the most extensively used class of chromophore in a large variety of applications.

Self-Assembled Cyclophane-Type Copper(I) Complexes of 2,4,6-Tris(diphenylphosphino)-1,3,5-triazine and Their Catalytic Application

The triazine-based trisphosphine, 2,4,6-tris(diphenylphosphino)-1,3,5-triazine (1) was prepared in improved yield by reacting cyanuric chloride with 3 equiv of trimethylsilyldiphenylphosphine. The solid-state structure of 1 showed short intermolecular P···P contacts of 3.362 Å, which is significantly shorter than the sum of the van der Waals radii of phosphorus atoms (3.6 Å). The reaction of 2,4,6-tris(diphenylphosphino)-1,3,5-triazine (1) with copper(I) salts in a 2:3 molar ratio yielded various cyclophane-type complexes in quantitative yield. The solid-state structures of these clusters have been found to depend on the size of the halide ions, the solvent employed, and the reaction conditions. Copper(I) chloride formed a monomeric metallocyclophane, whereas copper(I) bromide and copper(I) iodide derivatives preferred dimeric and 1D-polymeric structures, respectively. The tricationic complexes derived from Cu(I) ion and 2,4,6-tris(diphenylphosphino)-1,3,5-triazine also adopted monomeric metallocyclophane structures. These complexes have been employed in the A(3) coupling reaction under microwave irradiation. The copper(I) iodide derivative showed excellent catalytic efficiency.

Accurate Diffusion Coefficients of Organosoluble Reference Dyes in Organic Media Measured by Dual-Focus Fluorescence Correlation Spectroscopy

Dual-focus fluorescence correlation spectroscopy (2fFCS) is a versatile method to determine accurate diffusion coefficients of fluorescent species in an absolute, reference-free manner. Whereas (either classical or dual-focus) FCS has been employed primarily in the life sciences and thus in aqueous environments, it is increasingly being used in materials chemistry, as well. These measurements are often performed in nonaqueous media such as organic solvents. However, the diffusion coefficients of reference dyes in organic solvents are not readily available. For this reason we determined the translational diffusion coefficients of several commercially available organosoluble fluorescent dyes by means of 2fFCS. The selected dyes and organic solvents span the visible spectrum and a broad range of refractive indices, respectively. The diffusion coefficients can be used as absolute reference values for the calibration of experimental FCS setups, allowing quantitative measurements to be performed. We show that reliable information about the hydrodynamic dimensions of the fluorescent species (including noncommercial compounds) within organic media can be extracted from the 2fFCS data.

Highly Emissive Nanoparticles Based on AIE-Active Molecule and PAMAM Dendritic "Molecular Glue"

The highly emissive nanoparticles Gn-TCMPE (n = 0-4) were prepared by using PAMAM dendrimers as "molecular glue" to adhere an AIE-active molecule tetra(4-(carboxymethoxy)phenyl)ethylene (TCMPE). The electrostatic interaction of ammonium-carboxylate ion pairs provides a driving force between TCMPE and PAMAM dendrimers to form the nanoparticles Gn-TCMPE (n = 0-4), which is validated by the FTIR and (1)H NMR spectra. The formation of nanoparticles dramatically blocks the nonradiative pathway and enhances the fluorescence of TCMPE. The quantum yields of Gn-TCMPE gradually boost at first and then reach to a plateau with increasing the generation of PAMAM dendrimers, and the highest absolute quantum yields are obtained to be 0.42 and 0.64 for Gn-TCMPE (n = 2-4) in methanol dispersion and solid phases, respectively. The fluorescence of the nanoparticles can be tuned by addition of trifluoroacetic acid (TFA). Furthermore, the G4-TCMPE has been successfully applied to selectively image cytoplasm of Hela cells with excellent photostability and low cytotoxicity. This study provides a novel noncovalent strategy for developing highly emissive and robust organic materials fitting for cell fluorescence imaging.

Photoresponsive self-assembled hexameric capsules based on calix[4]resorcinarenes bearing azobenzene dendron conjugates as side chains

Calix[4]resorcinarenes with azobenzene dendron conjugates achieve control of the assembly–disassembly–reassembly process of the hydrogen-bonded hexameric capsules by a light stimulus.

The polar side of polyphenylene dendrimers

The site-specific functionalization of poly(phenylene) dendrimers can produce macromolecules with a range of different polarities.

Covalent attachment and release of small molecules from functional polyphenylene dendrimers

Herein, we report the synthesis of 2nd generation PPDs functionalized with free thiol moieties within the scaffold, which were used as anchor points for the covalent attachment of guest species (p-nitrophenol derivatives) through the oxidative formation of disulfide linkages. The disulfide bonds were then cleaved under reductive conditions using dithiothreitol to discharge the molecules.

Perylene-cored star-shaped polycations for fluorescent gene vectors and bioimaging

Two star polycations, poly(2-aminoethyl methacrylate) (PAEMA, P1) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA, P2), have been synthesized with perylene diimide (PDI) as the central fluorophore. (1)H NMR and (13)C NMR are used to confirm the successful synthesis of a macromolecular initiator. Using ATRP strategy, P1 and P2 are obtained with narrow molecular weight distribution. The star polymers have good fluorescence properties in aqueous solution, which provides fluorescent tracing and imaging during gene delivery. Both P1 and P2 can efficiently condense DNA into stable nanoparticles. Transfection studies demonstrate that P1 and P2 deliver DNA into live cells with higher efficiency and lower cytotoxicity than polyethylenimine (PEI, 25 kDa). P2 shows higher capacity for gene delivery than P1 due to its better buffering and faster rate of cellular internalization.

Evolution of graphene molecules: structural and functional complexity as driving forces behind nanoscience

The evolution of nanoscience is based on the ability of the fields of chemistry and physics to share competencies through mutually beneficial collaborations. With this in mind, in this Perspective, I describe three classes of compounds: rylene dyes, polyphenylene dendrimers, as well as nanographene molecules and graphene nanoribbons, which have provided a superb platform to nurture these relationships. The synthesis of these complex structures is demanding but also rewarding because they stimulate unique investigations at the single-molecule level by scanning tunneling microscopy and single-molecule spectroscopy. There are close functional and structural relationships between the molecules chosen. In particular, rylenes and nanographenes can be regarded as honeycomb-type, discoid species composed of fused benzene rings. The benzene ring can thus be regarded as a universal modular building block. Polyphenylene dendrimers serve, first, as a scaffold for dyes en route to multichromophoric systems and, second, as chemical precursors for graphene synthesis. Through chemical design, it is possible to tune the properties of these systems at the single-molecule level and to achieve nanoscale control over their self-assembly to form multifunctional (nano)materials.

Tin-functionalized azobenzenes as nucleophiles in Stille cross-coupling reactions

The metalation of azobenzene by halogen-metal exchange typically leads to a reduction of the azo group to give hydrazine derivatives as major byproducts, instead of the desired metalated azobenzene species. In cross-coupling reactions, azobenzenes therefore usually serve as electrophiles, which greatly limits the scope of the reaction. To solve this problem, we have developed a mild and fast method to stannylate azobenzenes in high yields. This research shows that these stannylated azobenzenes can be used as nucleophilic components in Stille cross-coupling reactions with aryl bromides. The cross-coupling products were obtained in high yields ranging from 70 to 93%. With this reversal of the nucleophilic and electrophilic components, cross-coupling products are now accessible in which the aromatic rings coupled to the azobenzene bear functional groups that are sensitive to metalation.

Systemically interfering with immune response by a fluorescent cationic dendrimer delivered gene suppression

A water-soluble, fluorescent, cationic dendrimer systemically delivers dsRNA into insect cells and tissues, resulting in the suppression of the immune gene.