Carbon Cationic Relay via Superelectrophiles: Synthesis of Spiro‑diazafluorenes

Superelectrophilic-initiated carbon cationic relay reactions of diazafluorenones with phenols were developed to provide strategically novel and atom-economic access to spirodiazafluorenes via tandem Friedel–Crafts reaction, nucleophilic addition, and intramolecular cyclization sequences. A range of spirodiazafluorenes that are difficult to synthesize with traditional protocols has been constructed successfully in middle to high yields using this method

Synthesis of Fluoren-9-ones and Ladder-Type Oligo‑<i>p</i>‑phenylene Cores via Pd-Catalyzed Carbonylative Multiple C–C Bond Formation

A new route to various substituted fluoren-9-ones has been developed via an efficient Pd-catalyzed carbonylative multiple C–C bond formation. Under a CO atmosphere, using commercially available aryl halides and arylboronic acids as substrates, this three-component reaction proceeded smoothly in moderate to excellent yields with good functional-group compatibility. The mechanistic investigations suggested a sequential process for the reaction that forms <i>o</i>-bromobiaryls in the first stage followed by a cyclocarbonylation reaction. This chemistry has been successfully extended to construct ladder-type oligo-<i>p</i>-phenylene cores

Surfactant Charge Mediated Shape Control of Nano- or Microscaled Coordination Polymers: The Case of Tetrapyridylporphine Based Metal Complex

In this work, CuTPyP (TPyP = 5,10,15,20-tetrapyridylporphine) single crystalline 2D nanoplates and 3D polyhedra of nano-octahedrons and microspindles can be selectively obtained by changing the type as well as the concentration of the surfactant via a simple surfactant-assisted chemical solution method at room temperature. Under anionic surfactant of sodium dodecyl sulfate (SDS), high purity uniform nanoplates were obtained, while under cationic surfactant of cetyltrimethylammonium bromide or tetrabutylammonium bromide, monodispersed microspindles and nano-octahedrons were obtained. The as synthesized products are characterized by UV–vis spectroscopy, fluorescence emission spectroscopy, X-ray diffraction pattern, scanning electron microscopy, and transmission electron microscopy. The crystal growth mechanism in the presence of either positively charged or negatively charged surfactant was studied by changing the preparation parameters. The rational shaping mechanism for different surfactants was thus promoted. This work provides a simple and mild approach to obtain high-quality 2D MTPyP nanocrystals through an anionic surfactant controlled synthesis process. It should be transferable to the shape control of nano- or microscaled metal–organic materials with related growth mechanisms

Palladium-Catalyzed Direct Arylation of C–H Bond To Construct Quaternary Carbon Centers: The Synthesis of Diarylfluorene

A novel Pd-catalyzed C–H functionalization reaction was developed to construct a quaternary carbon center with high yield. This reaction provides an efficient method for the synthesis of 9,9′-diarylfluorenes by direct arylation of monoarylfluorene

Synergistic Effects of Self-Doped Nanostructures as Charge Trapping Elements in Organic Field Effect Transistor Memory

Despite remarkable advances in the development of organic field-effect transistor (OFET) memories over recent years, the charge trapping elements remain confined to the critical electrets of polymers, nanoparticles, or ferroelectrics. Nevertheless, rare reports are available on the complementary advantages of different types of trapping elements integrated in one single OFET memory. To address this issue, we fabricated two kinds of pentacene-based OFET memories with solution-processed amorphous and β-phase poly­(9,9-dioctyl­fluorene) (PFO) films as charge trapping layers, respectively. Compared to the amorphous film, the β-PFO film has self-doped nanostructures (20–120 nm) and could act as natural charge trapping elements, demonstrating the synergistic effects of combining both merits of polymer and nanoparticles into one electret. Consequently, the OFET memory with β-PFO showed nearly 26% increment in the storage capacity and a pronounced memory window of ∼45 V in 20 ms programming time. Besides, the retention time of β-PFO device extended 2 times to maintain an ON/OFF current ratio of 10³, indicating high bias-stress reliability. Furthermore, the β-PFO device demonstrated good photosensitivity in the 430–700 nm range, which was attributed to the additive effect of smaller bandgap and self-doped nanostructures of β-phase. In this regard, the tuning of molecular conformation and aggregation in a polymer electret is an effective strategy to obtain a high performance OFET memory

Dipole Moment Effect of Cyano-Substituted Spirofluorenes on Charge Storage for Organic Transistor Memory

As a fascinating information storage device, organic transistor memory based on molecular charge storage elements (MCSEs) has attracted great research interest. However, the charge storage mechanism of MCSEs is ambiguous due to their complex charge dynamic behaviors. Herein, the dipole moment effects on the charge trapping process and the performance of transistor memory are revealed based on cruciform spiro­[fluorene-9,9′-xanthene] (SFXs), incorporating cyano moieties, as the typical electron-withdrawing substitution. The characterization of electrostatic potential (ESP) calculation, UV–vis, photoluminescence, and crystallography of SFXs shows the SFXs MCSEs with weaker dipole moment through symmetrical substitution. A series of prototype transistor memories based on SFXs exhibit an erasable type feature with smart photoresponsive behavior. The weaker dipole moment ones possess larger memory window (∼40 V), higher charge trapping density (>1 × 10¹³ cm^–2), and higher programming speed (10¹⁴–10¹¹ cm^–2 s^–1). The hole trapping process is dominated by the dipole moment rather than the charge dissipation when compared with different SFXs at the same HOMO level. Rather good charge retention property (>10⁴ s) and large on/off ratio (∼10⁴) are obtained by blending SFXs with polymer dielectrics in optimized devices. The dipole moment effects on the charge trapping behavior provide not only the design of high performance transistor memory but also the smart information encryption in future data storage

Polyfluorene (PF) Single-Chain Conformation, β Conformation, and Its Stability and Chain Aggregation by Side-Chain Length Change in the Solution Dynamic Process

The effects of alkyl side-chain length with different carbon atom number, called poly­(9,9di-hexlyfluorene) (PF6), poly­(9,9-diheptylfluorene) (PF7), poly­(9,9-dioctylfluorene) (PF8), poly­(9,9-dinonylfluorene) (PF9), and poly­(9,9-didecylfluorene) (PF10), on the polyfluorene (PF) single-chain conformation, β conformation, and its stability and chain aggregation in the solution dynamic process were systematically investigated by dynamic/static light scattering, UV–vis absorption spectra, photoluminescence spectra, and scanning electron microscopy. β conformation was the low-energy chain conformation, and its characteristic peak was at 437, 427, and 428 nm in the UV–vis spectrum of PF8, PF9, and PF10, respectively. It was interestingly found that the shape parameters (<i>R</i>_g/<i>R</i>_h) (i.e., ratio of radius of gyration (<i>R</i>_g) and hydrodynamic radius (<i>R</i>_h)) of PF single chains in toluene solution showed an odd–even property with the increase in side-chain length, which revealed that PF chains with even carbon atoms were more rigid than those with odd carbon atoms. The highest contents of β conformation were all ∼42% in PF8, PF9, and PF10 toluene/ethanol mixed solutions, but PF8 most easily formed the β conformation, PF9 followed, and PF10 was last. It was first found that the β-conformation formation and content were strongly connected to the chain packing density but not to aggregation size. High chain packing density was more advantageous to β-conformation formation; it had been well proved by static fractal dimension (<i>d</i>_f), reflecting the compactness of chain aggregation (i.e., chain packing density) and the chain self-similarity, and calculated by exponential law from SLS. Besides, it was also found that the β-conformation content could be stabilized at the maximum value range (42%) in the high ethanol content (80%) and independent of the side-chain length even after placing for 21 days, whereas in lower ethanol content (30 and 40%), the β-conformation content could also be stabilized in two different time stages. The conclusions are significant to understand deeply the solution dynamics process of film formation based on condensed matter physics of the conjugated polymer to control its condensed matter structure to achieve photoelectric devices with high carrier mobility, stability, and efficiency

Molecular Dual-Rotators with Large Consecutive Emission Chromism for Visualized and High-Pressure Sensing

Low-cost, stable, highly sensitive, and easy-to-equip fluorescent high-pressure sensors are always attractive in both industrial and scientific communities. Organic emitting materials with pressure-dependent bathochromisms usually exhibit prominent mechanoluminescence, due to disturbance of intermolecular packing. This hinders their applications in stable and robust pressure sensing. In this work, we have developed a mechanically stable organic molecular pressure sensor, caused by intramolecular consecutive rotations by pressure, which exhibit large and eye-detectable emission bathochromism from yellow-green to red fluorescence and can be used for 0–15 GPa pressure sensing. The emission bathochromism shows good linear relationship with pressure, exhibiting a high linear coefficient of 9.1 nm/GPa. Moreover, this molecular sensor exhibits high thermal and mechanical stabilities, indicating good potentials for robust and outdoor applications

Self-Assembled Chiral Nanofibers from Ultrathin Low-Dimensional Nanomaterials

Despite many developed methods, it still remains a challenge to provide a simple and general strategy for the controlled preparation of chiral nanostructures. Here we report a facile and universal approach for the high-yield and scalable preparation of chiral nanofibers based on the self-assembly of various ultrathin one-dimensional and two-dimensional nanomaterials in vigorously stirred polymeric solutions. The obtained chiral nanofibers can be further transformed to same-handed chiral nanorings. As a proof-of-concept application, chiral MoS₂ and multiwalled carbon nanotube nanofibers were used as promising active layers for flexible nonvolatile data storage devices. Impressively, the chiral MoS₂ nanofiber-based memory device presents a typical nonvolatile flash memory effect with excellent reproducibility and good stability. Our method offers a general route for the preparation of various functional chiral nanostructures that might have wide applications

Label-Free Dynamic Detection of Single-Molecule Nucleophilic-Substitution Reactions

The mechanisms of chemical reactions, including the transformation pathways of the electronic and geometric structures of molecules, are crucial for comprehending the essence and developing new chemistry. However, it is extremely difficult to realize at the single-molecule level. Here, we report a single-molecule approach capable of electrically probing stochastic fluctuations under equilibrium conditions and elucidating time trajectories of single species in non-equilibrated systems. Through molecular engineering, a single molecular wire containing a functional center of 9-phenyl-9-fluorenol was covalently wired into nanogapped graphene electrodes to form stable single-molecule junctions. Both experimental and theoretical studies consistently demonstrate and interpret the direct measurement of the formation dynamics of individual carbocation intermediates with a strong solvent dependence in a nucleophilic-substitution reaction. We also show the kinetic process of competitive transitions between acetate and bromide species, which is inevitable through a carbocation intermediate, confirming the classical mechanism. This unique method creates plenty of opportunities for carrying out single-molecule dynamics or biophysics investigations in broad fields beyond reaction chemistry through molecular design and engineering