Magnetic Multistability in an Anion‐Radical Pimer

Radical pimers are the simplest and most important models for studying charge‐transfer processes and provide deep insight into π‐stacked organic materials. Notably, radical pimer systems with magnetic bi‐ or multistability may have important applications in switchable materials, thermal sensors, and information‐storage media. However, no such systems have been reported. Herein, we describe a new pimer consisting of neutral N‐(n‐propyl) benzene triimide ([BTI‐3C]) and its anionic radical ([BTI‐3C]^?.) that exhibits rare magnetic multistability. The crystalline pimer was readily synthesized by reduction of BTI‐3C with cobaltocene (CoCp₂). The transition occurred with a thermal hysteresis loop that was 27 K wide in the range of 170–220 K, accompanied by a smaller loop with a width of 25 K at 220–242 K. The magnetic multistability was attributed to slippage of the π‐stacked BTI structures and entropy‐driven conformational isomerization of the side propyl chains in the crystalline state during temperature variation.     

Tailored Solution-Based N-heterotriangulene Thin Films: Unravelling the Self-Assembly

The ability of a series of bridged triarylamines, so-called N-heterotriangulenes, to form multilayer-type 2D-extended films via a solution-based processing method was examined using complementary microscopic techniques. We found that the long-range order, crystallinity, and layer thickness decisively depend on the nature of the substituents attached to the polycyclic backbone. Owing to their flat core unit, compounds exhibiting a carbonyl unit at the bridge position provide a superior building block as compared to thioketone-bridged derivatives. In addition, nature and length of the peripheral substituents affect the orientation of the aromatic core unit within highly crystalline films. Hence, our results stress the significance of a suitable molecular framework and provide deeper understanding of structure formation in 2D-confined surroundings for such compounds.     

Morphology of Imidazolium‐Based Ionic Liquids as Deposited by Vapor Deposition: Micro‐/Nanodroplets and Thin Films

The morphology of micro‐ and nanodroplets and thin films of ionic liquids (ILs) prepared through physical vapor deposition is presented. The morphology of droplets deposited on indium‐tin‐oxide‐coated glass is presented for the extended 1‐alkyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C_nC₁im][Ntf₂]; n=1–8) series, and the results show the nanostructuration of ILs. The use of in‐vacuum energetic particles enhances/increases the nanodroplets mobility/coalescence mechanisms and can be a pathway to the fabrication of thin IL films.     

Defect‐Controlled Preparation of UiO‐66 Metal–Organic Framework Thin Films with Molecular Sieving Capability

Metal–organic framework (MOF) UiO‐66 thin films are solvothermally grown on conducting substrates. The as‐synthesized MOF thin films are subsequently dried by a supercritical process or treated with polydimethylsiloxane (PDMS). The obtained UiO‐66 thin films show excellent molecular sieving capability as confirmed by the electrochemical studies for redox‐active species with different sizes.     

Hydrogen‐Bonded Organic Aromatic Frameworks for Ultralong Phosphorescence by Intralayer π–π Interactions

Ultralong organic phosphorescence (UOP) based on metal‐free porous materials is rarely reported owing to rapid nonradiative transition under ambient conditions. In this study, hydrogen‐bonded organic aromatic frameworks (HOAFs) with different pore sizes were constructed through strong intralayer π–π interactions to enable ultralong phosphorescence in metal‐free porous materials under ambient conditions for the first time. Impressively, yellow UOP with a lifetime of 79.8 ms observed for PhTCz‐1 lasted for several seconds upon ceasing the excitation. For PhTCz‐2 and PhTCz‐3, on account of oxygen‐dependent phosphorescence quenching, UOP could only be visualized in N₂, thus demonstrating the potential of phosphorescent porous materials for oxygen sensing. This result not only outlines a principle for the design of new HOFs with high thermal stability, but also expands the scope of metal‐free luminescent materials with the property of UOP.     

A Radical Polymer as a Two‐Dimensional Organic Half Metal

Given that half‐metals are promising futuristic materials for spintronics, organic materials showing half‐metal character are highly desirable for spintronic devices, not only owing to their weak spin‐orbit and hyperfine interactions, but also their light and flexible properties. We predict that a two‐dimensional organic 2,4,6‐tri‐(1,3,5‐triazinyl)methyl radical polymer has half‐metallic properties as well as a spontaneous magnetic ordering at ambient temperature. The quantum transmission is studied based on the nonequilibrium Green function theory coupled with density functional theory. The half‐metallic property in the triazine‐based polymer depends mainly on the nature of the p‐band in contrast to of conventional half metals in which the nature of the d‐band is more important.     

有机半导体薄膜空间电荷分布对晶体管性能影响的研究进展

有机场效应晶体管(OFETs)是下一代柔性电子产业的基础元件,具有可弯曲、透明、低成本、可溶液加工等优良特性,并逐渐开始应用于生物传感器、柔性显示等领域。 然而,OFETs仍存在如工作电流小、跨导小、开关比低、空气稳定性差等问题,限制了其进一步的发展。 OFETs器件的性能主要受到导电沟道中电荷和电流分布的影响,若能通过外加手段,调控沟道中的电荷和电流分布,可能获得具有更高性能或新机理的器件。 本文结合课题组内的工作,对国内外该领域的最新进展进行综述和展望。     

Covalent Organic Framework for Improving Near‐Infrared Light Induced Fluorescence Imaging through Two‐Photon Induction

Fluorescent materials exhibiting two‐photon induction (TPI) are used for nonlinear optics, bioimaging, and phototherapy. Polymerizations of molecular chromophores to form π‐conjugated structures were hindered by the lack of long‐range ordering in the structure and strong π–π stacking between the chromophores. Reported here is the rational design of a benzothiadiazole‐based covalent organic framework (COF) for promoting TPI and obtaining efficient two‐photon induced fluorescence emissions. Characterization and spectroscopic data revealed that the enhancement in TPI performance is attributed to the donor‐π‐acceptor‐π‐donor configuration and regular intervals of the chromophores, the large π‐conjugation domain, and the long‐range order of COF crystals. The crystalline structure of TPI‐COF attenuates the π–π stacking interactions between the layers, and overcomes aggregation‐caused emission quenching of the chromophores for improving near‐infrared two‐photon induced fluorescence imaging.     

A Facile and Highly Efficient Approach to Obtain a Fluorescent Chromogenic Porous Organic Polymer for Lymphatic Targeting Imaging

Porous organic polymers have an open architecture, excellent stability, and tunable structural components, revealing great application potential in the field of fluorescence imaging, but this part of the research is still in its infancy. In this study, we aimed to tailor the physical and chemical characteristics of indocyanine green using sulfonic acid groups and conjugated fragments, and prepared amino-grafted porous polymers. The resulting material had excellent solvent and thermal stability, and possessed a relatively large pore structure with a size of 3.4 nm. Based on the synergistic effect of electrostatic bonding and π–π interactions, the fluorescent chromogenic agent, indocyanine green, was tightly incorporated into the pore cavity of POP solids through a one-step immersion method. Accordingly, the fluorescent chromogenic POP demonstrated excellent imaging capabilities in biological experiments. This preparation of fluorescent chromogenic porous organic polymer illustrates a promising application of POP-based solids in both fluorescence imaging and biomedicine applications.     

Transient Absorption Spectroscopy Studies on Polythiophene–Fullerene Bulk Heterojunction Organic Blend Films Sensitized with a Low‐Bandgap Polymer

Recently, the concept of near‐infrared sensitization is successfully employed to increase the light harvesting in large‐bandgap polymer‐based solar cells. To gain deeper insights into the operation mechanism of ternary organic solar cells, a comprehensive understanding of charge transfer–charge transport in ternary blends is a necessity. Herein, P3HT:PCPDTBT:PCBM ternary blend films are investigated by transient absorption spectroscopy. Hole transfer from PCPDTBT‐positive polarons to P3HT in the P3HT:PCPDTBT:PCBM 0.9:0.1:1 blend film can be visualized. This process evolves within 140 ps and is discussed with respect to the proposed charge‐generation mechanisms.

     

Site‐Directed Dimerization of Bowl‐Shaped Radical Anions to Form a σ‐Bonded Dibenzocorannulene Dimer

Designed site‐directed dimerization of the monoanion radicals of a π‐bowl in the solid state is reported. Dibenzo[a,g]corannulene (C₂₈H₁₄) was selected based on the asymmetry of the charge/spin localization in the C₂₈H₁₄^.? anion. Controlled one‐electron reduction of C₂₈H₁₄ with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs⁺(diglyme)}₂(C₂₈H₁₄?C₂₈H₁₄)^2?] ( 1 ), as revealed by single crystal X‐ray diffraction study performed in a broad range of temperatures. The C?C bond length between two C₂₈H₁₄^.? bowls (1.560(8) Å) measured at ?143 °C does not significantly change upon heating of the crystal to +67 °C. The single σ‐bond character of the C?C linker is confirmed by calculations. The trans‐disposition of two bowls in 1 is observed with the torsion angles around the central C?C bond of 172.3(5)° and 173.5(5)°. A systematic theoretical evaluation of dimerization pathways of C₂₈H₁₄^.? radicals confirmed that the trans‐isomer found in 1 is energetically favored.     

The structures of MOFs prepared from 1,3,5‐tris [4‐pyridylethynyl]‐benzene and a copper(I) perchlorate complex

Two copper(I)‐based frameworks of complexes {[Cu(L)₂(ClO₄)]?CH₃CN}( 2 ) and {[Cu(L)(ClO₄)]? 2CH₃CN} ( 3 ) (L = 1,3,5‐tris(4‐pyridylethynyl) benzene) were produced by reacting [Cu(MeCN)₄(ClO₄)] with different amounts of a ligand (L) using a hydrothermal method at temperatures of up to 130°C. The nitrogen atoms in the pyridine moieties of the ligand coordinate to the Cu(I) ion. The charge on the Cu(I) ion can be stabilized by extending the degree of conjugation in the system and by taking advantage of its highly symmetrical structure. The large degree of conjugation also supports numerous π–π interactions in the framework.     

Interplay between H‐Bonding and Preorganization in the Evolution of Self‐Assembled Systems

Cooperative π–π interactions and H‐bonding are frequently exploited in supramolecular polymerization; however, close scrutiny of their mutual interplay has been largely unexplored. Herein, we compare the self‐assembly behavior of a series of C₂‐ and C₃‐symmetrical oligophenyleneethynylenes differing in their amide topology (N‐ or C‐centered). This subtle structural modification brings about drastic changes in their photophysical and supramolecular properties, highlighting the reciprocal impact of H‐bonding vs. preorganization on the evolution and final outcome of supramolecular systems.     

Synthesis and Crystal Structure of [Cu2(H2O)2(phen)2(OH)2][Cu2(phen)2(OH)2(CO3)2] · 10 H2O with phen = 1,10‐phenanthroline

The blue copper complex [Cu₂(H₂O)₂(phen)₂(OH)₂][Cu₂(phen)₂(OH)₂(CO₃)₂] · 10 H₂O, which was prepared by reaction of 1,10‐phenanthroline monohydrate, CuCl₂ · 2 H₂O and Na₂CO₃ in the presence of succinic acid in CH3OH/H₂O at pH = 13.0, crystallized in the triclinic space group P1 (no. 2) with cell dimensions: a = 9.515(1) Å, b = 12.039(1) Å, c = 12.412(2) Å, α = 70.16(1)°, β = 85.45(1)°, γ = 81.85(1)°, V = 1323.2(2) ų, Z = 1. The crystal structure consists of dinuclear [Cu₂(H₂O)₂(phen)₂(OH)₂]²⁺ complex cations, dinuclear [Cu₂(phen)₂(OH)₂(CO₃)₂]^2– complex anions and hydrogen bonded H₂O molecules. In both the centrosymmetric dinuclear cation and anion, the Cu atoms are coordinated by two N atoms of one phen ligand, three O atoms of two μ‐OH groups and respectively one H₂O molecule or one CO₃^2– anion to complete distorted [CuN₂O₃] square‐pyramids with the H₂O molecule or the CO₃^2– anion at the apical position (equatorial d(Cu–O) = 1.939–1.961 Å, d(Cu–N) = 2.026–2.051 Å and axial d(Cu–O) = 2.194, 2.252 Å). Two adjacent [CuN₂O₃] square pyramids are condensed via two μ‐OH groups. Through the interionic hydrogen bonds, the dinuclear cations and anions are linked into 1D chains with parallel phen ligands on both sides. Interdigitation of phen ligands of neighboring 1D chains generated 2D layers, between which the hydrogen bonded water molecules are sandwiched.     

Twisted aromatics, 9-anthryl and 1-pyrenyl terpyridines organize into novel multi-directional ‘ladder-like’ motifs in the solid state

9-Anthryl and 1-pyrenyl terpyridines (1 and 2, respectively), key precursors for the design of novel fluorescent sensors have been synthesized and characterized by ¹H NMR, mass spectroscopy and X-ray crystallography. Twisted molecular conformations for each 1 and 2 were observed in their single crystal structures. Energy minimization calculations for the 1 and 2 using the semi-empirical AM1 method show that the ‘twisted’ conformation is intrinsic to these systems. We observe interconnected networks of edge-to-face CHπ interactions, which appear to be cooperative in nature, in each of the crystal structures. The two twisted molecules, although having differently shaped polyaromatic hydrocarbon substituents, show similar patterns of edge-to-face CHπ interactions.The presently described systems comprise of two aromatic surfaces that are almost orthogonal to each other. This twisted or orthogonal nature of the molecules leads to the formation of interesting multi-directional ladder like supramolecular organizations. A combination of edge-to-face and face-to-face packing modes helps to stabilize these motifs. The ladder like architecture in 1 is helical in nature.     

Photoconductivity in Mesostructured Thin Films

Mesostructured silica films are widely studied due to their different structures, properties and variety of possible applications. Sodium dodecyl sulfate (SDS)-templated sol-gel silica films possess highly ordered lamellar phase structure. It is expected that molecules and polymer chains line up with these layered structures when incorporated into the films. Mesostructured thin films were doped with Dispersed Red 1 (DR1) and carbazole ((C₆H₄)₂NH)). The films were poled by corona discharge at 120 C. Absorption spectra were recorded as function of the polarization time. Dependence of the absorption coefficient with polarization time was fitted with a Langevin-Debye equation. It shows a saturation level after 60 minutes of polarization. We compare the efficiency of mesostructured thin films with that of amorphous films. The photoconductivity technique was used to determine the charge transport mechanism of these films. From current density versus electrostatic applied field, the parameters for the photovoltaic effect and photoconductivity were determined. Results of the mesostructured thin films are also compared to those of KNbO₃ crystals.     

Dissecting the concave–convex π‐π interaction in corannulene and sumanene dimers: SAPT(DFT) analysis and performance of DFT dispersion‐corrected methods

The characteristics of the concave–convex π‐π interactions are evaluated in 32 buckybowl dimers formed by corannulene, sumanene, and two substituted sumanenes (with S and CO groups), using symmetry‐adapted perturbation theory [SAPT(DFT)] and density functional theory (DFT). According to our results, the main stabilizing contribution is dispersion, followed by electrostatics. Regarding the ability of DFT methods to reproduce the results obtained with the most expensive and rigorous methods, TPSS‐D seems to be the best option overall, although its results slightly tend to underestimate the interaction energies and to overestimate the equilibrium distances. The other two tested DFT‐D methods, B97‐D2 and B3LYP‐D, supply rather reasonable results as well. M06‐2X, although it is a good option from a geometrical point of view, leads to too weak interactions, with differences with respect to the reference values amounting to about 4 kcal/mol (25% of the total interaction energy). © 2017 Wiley Periodicals, Inc.