Amino-Ene Click Reaction of Electron-Deficient π-Conjugated Molecules with Negative Activation Enthalpies.

An amino-ene click reaction is a type of aza-Michael addition reaction that is congruent with click chemistry in terms of its reaction efficiency and rate under mild conditions. The amino-ene click reaction is increasingly recognized as a prominent synthetic tool to form C-N bonds in the context of organic materials chemistry and polymer chemistry. Herein, an unconventional amino-ene click reaction with negative activation enthalpies, in which an electron-deficient π-conjugated molecule, such as a naphthalenediimide, reacts with an amine faster at lower temperatures is reported. The detailed study of the reaction mechanism reveals that the amino-ene click reaction proceeds via a pre-equilibrium reaction, the key to which is the formation of a stable reaction intermediate due to the solvation and charge delocalization on the π-core. By optimizing the reaction conditions, it was demonstrated that the amino-ene click reaction proceeded faster at 273 K than at 347 K, which was easily observed visually.

One-step synthesis of perylenediimides exhibiting near-infrared absorption and emission by amino-yne click reaction.

The facile synthesis of chromophores with near-infrared (NIR) absorption and emission is of particular interest due to their wide range of applications. Here we report a one-step synthesis of amino-functionalized perylenediimides exhibiting NIR absorption and emission via a catalyst-free amino-yne click reaction. We also demonstrate the post-modification of polyethylenimine by the click reaction, resulting in the formation of a polymeric NIR chromophore with an emission peak at 913 nm in the solid state.

Cooperative self-assembling process of core-substituted naphthalenediimide induced by amino-yne click reaction.

We report a cooperative (i.e., nucleation-elongation) self-assembling process of a core-substituted naphthalenediimide induced by a catalyst-free amino-yne click reaction at 298 K. The self-assembling process was initiated immediately in the presence of nuclei (seeds). The combination of the click reaction and the seeded self-assembling process paves the way for precise control over supramolecular assemblies of electron-deficient π-systems.

Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroamination.

Implementing chemical reactivity into synthetic supramolecular polymers based on π-conjugated molecules has been of great interest to create functional materials with spatiotemporal dynamic properties. However, the development of an in situ chemical reaction within supramolecular polymers is still in its infancy, because one needs to design optimal π-conjugated monomers having excellent reactivity under mild conditions possibly without byproducts or a catalyst. Herein we report the synthesis of a supramolecular polymer based on ethynyl core-substituted naphthalenediimide (S-NDI2) molecules that react with various amines quantitatively in a nonpolar solvent, without a catalyst, at 298 K. Most interestingly, the in situ reaction of the S-NDI2 supramolecular polymer with a linear aliphatic diamine proceeded much faster than the homogeneous reaction of a monomeric naphthalenediimide with the same diamine, affording diamine-linked S-NDI2 oligomers and polymers. The acceleration of in situ hydroamination was presumably due to rapid intra-supramolecular cross-linking between ethynyl and amino groups fixed in close proximity within the supramolecular polymer. Such intra-supramolecular cross-linking did not occur efficiently with an incompatible diamine. The systematic kinetic studies of in situ catalyst-free hydroamination within supramolecular polymers provide us with a useful, facile and versatile tool kit for designing dynamic supramolecular polymeric materials based on electron-deficient π-conjugated monomers.

Postsynthetic Defect Formation in Three-Dimensional Hofmann-Type Coordination Polymers and Its Impact on Catalytic Activity.

We report a systematic investigation of postsynthetic defect formation in Hofmann-type coordination polymers M(pz)[M'(CN)4] (M = Fe2+, Co2+, Ni2+; M' = Pd2+, Pt2+; pz = pyrazine). These compounds readily undergo selective ligand exchange at the pyrazine site when immersed in methanol (MeOH) at ambient temperature. The ligand exchange changes the chemical formula to M(pz)1-x(MeOH)2x[M'(CN)4] (0 < x < 0.3), affording a defective coordination environment around the M ions. The defect concentration is highly dependent on the combination of the metal ions and solvent species, reaching the defect concentration of ca. 30% (x ∼ 0.3) at maximum. The magnetic state of one such coordination polymer gives an additional control of the defect formation, making the compound less susceptible to the ligand exchange at the low-spin state. Structures that form the defects at a high concentration function as catalysts and promote an acetalization reaction heterogeneously by providing Lewis acidic sites. The solvent-dependent character of the defect formation can be used to control the catalytic activity of the active compounds, demonstrating a facile defect engineering for functionalizing solid materials.

Self-Assembled Organic Cations-Assisted Band-Edge Tailoring in Bismuth-Based Perovskites for Enhanced Visible Light Absorption and Photoconductivity.

Bismuth-based zero-dimensional perovskites garner high research interest because of their advantages, such as excellent moisture stability and lower toxicity in comparison to lead-based congeners. However, the wide optical bandgap (>2 eV) and poor photoconductivity of these materials are the bottlenecks for their optoelectronic applications. Herein, we report a combined experimental and theoretical study of the structural features and optoelectronic properties of two novel and stable zero-dimensional bismuth perovskites: (biphenyl bis(methylammonium))1.5BiI6·2H2O (BPBI) and (naphthalene diimide bis(ethylammonium))1.5BiI6·2H2O (NDBI). NDBI features a remarkably narrower bandgap (1.82 eV) than BPBI (2.06 eV) because of the significant orbital contribution of self-assembled naphthalene diimide cations at the band edges of NDBI. Further, the FP-TRMC analysis revealed that the photoconductivity of NDBI is about 3.7-fold greater than that of BPBI. DFT calculations showed that the enhanced photoconductivity in NDBI arises from its type-IIa band alignment, whereas type-Ib alignment was seen in BPBI.

Dynamics of Meso-Chiral Interconversion in a Butterfly-Shape Overcrowded Alkene Rotor Tunable by Solvent Properties.

Elucidation of dynamics of molecular rotational motion is an essential part and challenging area of research. We demonstrate reversible diastereomeric interconversion of a molecular rotor composed of overcrowded butterfly-shape alkene (FDF). Its inherent dual rotatory motion (two rotors, one stator) with interconversion between two diastereomers, chiral trans-FDF and meso cis-FDF forms, has been examined in detail upon varying temperatures and solvents. The free energy profile of 180° revolution of one rotor part has a bimodal shape with unevenly positioned maxima (transition states). FDF in aromatic solvents adopts preferentially meso cis-conformation, while in non-aromatic solvents a chiral trans-conformation is more abundant owing to the solvent interactions with peripheral hexyl chains (solvophobic effect). Moderate correlations between the trans-FDF/cis-FDF ratio and solvent parameters, such as refractive index, polarizability, and viscosity were found.

Ultraviolet Light-Densified Oxide-Organic Self-Assembled Dielectrics: Processing Thin-Film Transistors at Room Temperature.

Low-temperature, solution-processable, high-capacitance, and low-leakage gate dielectrics are of great interest for unconventional electronics. Here, we report a near room temperature ultraviolet densification (UVD) methodology for realizing high-performance organic-inorganic zirconia self-assembled nanodielectrics (UVD-ZrSANDs). These UVD-ZrSAND multilayers are grown from solution in ambient, densified by UV radiation, and characterized by X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and capacitance measurements. The resulting UVD-ZrSAND films exhibit large capacitances of >700 nF/cm2 and low leakage current densities of <10-7 A/cm2, which rival or exceed those synthesized by traditional thermal methods. Both the p-type organic semiconductor pentacene and the n-type metal oxide semiconductor In2O3 were used to investigate UVD-ZrSANDs as the gate dielectric in thin-film transistors, affording mobilities of 0.58 and 26.21 cm2/(V s), respectively, at a low gate voltage of 2 V. These results represent a significant advance in fabricating ultra-thin high-performance dielectrics near room temperature and should facilitate their integration into diverse electronic technologies.

Amino-Functionalization of Vinyl-Substituted Aromatic Diimides by Quantitative and Catalyst-Free Hydroamination*.

Development of facile and versatile synthetic tools for decorating π-conjugated molecules has attracted considerable interest because of their potential application in creating novel functional π-systems. Reported herein are quantitative catalyst-free hydroamination reactions of a series of aromatic diimide compounds having vinyl groups at the π-core, which have been confirmed by NMR, UV-vis absorption spectroscopy, mass analysis, and single-crystal X-ray structural analysis. Kinetic studies revealed that the hydroamination reaction of a vinyl-substituted naphthalenediimide with an aliphatic amine proceeded rapidly under benign conditions. Similarly, the two vinyl groups attached to aromatic diimides reacted with amines simultaneously, resulting in the formation of amine bisadducts and macromolecules. An amino group appended perylenediimide through an ethylene spacer at the π-core exhibited distinct fluorescence switching in response to acid and base.

Immobilization of Ethynyl-π-Extended Electron Acceptors with Amino-Terminated SAMs by Catalyst-Free Click Reaction.

Surface modification of SiO2 using a catalyst-free quantitative reaction between an amine and an ethynyl-π-extended naphthalenediimide was investigated. A post-reaction method, in which the catalyst-free reaction was performed at the surface after the formation of amino-terminated self-assembled monolayers (SAMs), resulted in dense, uniform modification of the SiO2 surface with the naphthalenediimide molecules. Both X-ray reflectivity and angle-resolved X-ray photoemission spectroscopy showed consistent results for the layer thickness and density. In contrast, a pre-reaction method, in which an amino-silane and the ethynyl-π-extended naphthalenediimide reacted first and then formed a SAM, afforded a sparse SAM on the SiO2 surface, probably due to the steric hindrance of the naphthalenediimide moieties. The in situ decoration of the SiO2 surface by a catalyst-free quantitative reaction offers a facile route for modifying surface properties with various π-conjugated molecules suitable for many applications.

Discrete π Stack of a Tweezer-Shaped Naphthalenediimide-Anthracene Conjugate.

The design and synthesis of a tweezer-shaped naphthalenediimide (NDI)-anthracene conjugate (2NDI) are reported. In the structure of the closed form (πNDI ⋅⋅⋅πNDI stack) of 2NDI, which was elucidated by single-crystal XRD, the existence of C-H⋅⋅⋅O hydrogen bonding involving the nearest carbonyl oxygen atom of an NDI unit was suggested. The tunability of πNDI ⋅⋅⋅πNDI interactions was studied by means of UV/Vis absorption, fluorescence and NMR spectroscopy and molecular modelling. This revealed that the πNDI ⋅⋅⋅πNDI interactions in 2NDI affect the absorption and emission properties depending on the temperature. Furthermore, in polar solvents, 2NDI prefers the stronger πNDI ⋅⋅⋅πNDI stack, whereas the πNDI ⋅⋅⋅πNDI interaction is diminished in nonpolar solvents. Importantly, the conformational variations of 2NDI can be reversibly switched by variation in temperature, and this suggests potential application for fluorogenic molecular switches upon temperature changes.

Conformational Dynamics of Monomer- versus Dimer-like Features in a Naphthalenediimide-Based Conjugated Cyclophane.

The design and synthesis of an enantiomeric pair of 1,8-diethynylanthracene-bridged naphthalenediimide (NDI)-based cyclophanes (Cyclo-NDIs) are reported. Each enantiomer of Cyclo-NDI exhibits a circularly polarized luminescence signal with a relatively large luminescence dissymmetry factor (glum =±8×10-3 ). We have further investigated the modulation of through-space electronic communication between co-facially oriented NDIs in a discrete Cyclo-NDI with changes in the temperature. Tuning of the electronic communication results from the conformational transformation of monomer- versus dimer-like features of Cyclo-NDI, as confirmed by UV/Vis, fluorescence, circular dichroic, and NMR spectroscopic analysis. The temperature-dependent optical response in the Cyclo-NDI through the conformational transformation could be utilized as a highly sensitive and reversible optical thermometer in a wide temperature range (100 to -80 °C).

A Spin-Active, Electrochromic, Solvent-Free Molecular Liquid Based on Double-Decker Lutetium Phthalocyanine Bearing Long Branched Alkyl Chains.

Synthesis and characterization of a novel, multifunctional, solvent-free room-temperature liquid based on alkylated double-decker lutetium(III) phthalocyanine (Pc2 Lu) are described. Lowering of the melting point and viscosity of intrinsically solid Pc2 Lu compounds has been achieved through the attachment of flexible, bulky, and long branched-alkyl chains, that is, thio-2-octyldodecyl, to the periphery of the Pc2 Lu unit. The embedded Pc2 Lu unit maintains its inherent molecular functions, such as spin-active nature and electrochromic behavior in the liquid state. Comparison of the properties with a solid-like Pc2 Lu derivative, functionalized with shorter alkyl chains, that is, thio-2-ethylhexyl, underlines the importance of the hampering effect on the π-π interactions of neighboring Pc2 Lu molecules by bulkier and longer branched-alkyl chains. This study could possibly pave the way for novel multifunctional liquids whose spin-activities are associated with their rheological or optoelectronic properties.

Red-Green-Blue Trichromophoric Nanoparticles with Dual Fluorescence Resonance Energy Transfer: Highly Sensitive Fluorogenic Response Toward Polyanions.

A red-green-blue (RGB) trichromophoric fluorescent organic nanoparticle exhibiting multi-colour emission was constructed; the blue-emitting cationic oligofluorene nanoparticle acted as an energy-donor scaffold to undergo fluorescence resonance energy transfer (FRET) to a red-emitting dye embedded in the nanoparticle (interior FRET) and to a green-emitting dye adsorbed on the surface through electrostatic interactions (exterior FRET). Each FRET event occurs independently and is free from sequential FRET, thus the resultant dual-FRET system exhibits multi-colour emission, including white, in aqueous solution and film state. A characteristic white-emissive nanoparticle showed visible responses upon perturbation of the exterior FRET efficiency by acceptor displacement, leading to highly sensitive responses toward polyanions in a ratiometric manner. Specifically, our system exhibits high sensitivity toward heparin with an extremely low detection limit.

Supramolecular Assemblies of Ferrocene-Hinged Naphthalenediimides: Multiple Conformational Changes in Film States.

We design a new naphthalenediimide (NDI) π-system, NDI-Fc-NDI, having a ferrocene linker as a hinge unit and long alkyl chains as supramolecular assembling units. The NDI units are "directionally flexible" in concert with the pivoting motion of the ferrocene unit with a small rotational barrier. The NDI units rotate around the ferrocene unit faster than the NMR time scale in solution at room temperature. UV-vis absorption, synchrotron X-ray diffraction, and atomic force microscope studies reveal that NDI-Fc-NDI forms a fibrous supramolecular assembly in solution (methylcyclohexane and highly concentrated chloroform) and film states, wherein the NDI units are in the slipped-stack conformation. The NDI-Fc-NDI supramolecular assembly in the film state exhibits multiple phase transitions associated with conformational changes at different temperatures, which are confirmed by differential scanning calorimetry, polarized optical microscopy, and temperature-dependent X-ray diffraction. Such thermal transitions of NDI-Fc-NDI films also induce changes in the optical and electronic properties as revealed by UV-vis absorption and photoelectron yield spectroscopies, respectively. The thermal behaviors of NDI-Fc-NDI, realized by the unique molecular design, are considerably different from the reference compounds such as an NDI dimer connected with a flexible 1,4-butylene linker. These results provide us with a plausible strategy to propagate the molecular dynamics of the π-system into macroscopic properties in film states; the key factors are (i) the supramolecular alignment of molecular switching units and (ii) the directional motion of the switching units perpendicular to the supramolecular axis.

Ferrocene-Substituted Naphthalenediimide with Broad Absorption and Electron-Transport Properties in the Segregated-Stack Structure.

A new naphthalenediimide (NDI) molecule, where two ferrocene (Fc) units were directly attached to both imide nitrogens (Fc-NDI-Fc), was synthesized. The Fc units provide high crystallinity to Fc-NDI-Fc with good solubility to conventional organic solvents. The Fc units also work as electron-donating substituents, in contrast to the electron-deficient NDI unit, resulting in broad charge-transfer absorption of Fc-NDI-Fc from the UV region to 1500 nm in the solid state. The crystal structure analysis revealed that Fc-NDI-Fc formed a segregated-stack structure. The DFT calculation based on the crystal structure showed that the NDI π-orbitals extended over two axes. The extended π-network of the NDI units led to the electron-transport properties of Fc-NDI-Fc, which was confirmed using a flash-photolysis time-resolved microwave conductivity technique.

Phosphorescence from a pure organic fluorene derivative in solution at room temperature.

A fluorene derivative having both bromo and formyl groups exhibited bright phosphorescence emission in common organic solvents at room temperature. The absolute phosphorescence quantum yield reached 5.9% in chloroform at 298 K. When the fluorene derivative was incorporated into a poly(methyl methacrylate) film, the phosphorescence emission was similarly observed even under air at room temperature for over five days.

Synthesis and photodynamics of fluorescent blue BODIPY-porphyrin tweezers linked by triazole rings.

Novel zinc porphyrin tweezers in which two zinc porphyrins were connected with π-conjugated boron dipyrromethenes (BDP meso-Por(2) and BDP ß-Por(2)) through triazole rings were synthesized to investigate the photoinduced energy transfer and electron transfer. The UV-vis spectrum of BDP ß-Por(2) which has less bulky substituents than BDP meso-Por(2) exhibits splitting of the Soret band as a result of the interaction between porphyrins of BDP ß-Por(2) in the excited state. Such interaction between porphyrins of both BDP ß-Por(2) and BDP meso-Por(2) is dominant at room temperature, while the coordination of the nitrogen atoms of the triazole rings to the zinc ions of the porphyrins occurs at low temperature. The conformational change of the BDP-porphyrin composites was confirmed by the changes in UV-vis and fluorescence spectra depending on temperature. Photodynamics of BDP meso-Por(2) and BDP ß-Por(2) has also been investigated by laser flash photolysis. Efficient singlet-singlet energy transfer from the ZnP to the π-conjugated BDP moiety of both BDP meso-Por(2) and BDP ß-Por(2) occurred in opposite direction as compared to energy transfer from conventional BDP to ZnP due to the π-conjugation in nonpolar toluene. In polar benzonitrile, however, additional electron transfer occurred along with energy transfer.

Rhodium-catalyzed enantioselective synthesis, crystal structures, and photophysical properties of helically chiral 1,1'-bitriphenylenes.

The highly enantioselective synthesis of helically chiral 1,1'-bitriphenylenes has been achieved via rhodium-catalyzed double [2 + 2 + 2] cycloaddition of biaryl-linked tetraynes with 1,4-diynes (up to 93% ee). Crystal structures and photophysical properties of these helically chiral 1,1'-bitriphenylenes have also been studied.