Constructing Donor-Resonance-Donor Molecules for Acceptor-Free Bipolar Organic Semiconductors

Organic semiconductors with bipolar transporting character are highly attractive as they offer the possibility to achieve high optoelectronic performance in simple device structures. However, the continual efforts in preparing bipolar materials are focusing on donor-acceptor (D-A) architectures by introducing both electron-donating and electron-withdrawing units into one molecule in static molecular design principles. Here, we report a dynamic approach to construct bipolar materials using only electron-donating carbazoles connected by N-P=X resonance linkages in a donor-resonance-donor (D-r-D) structure. By facilitating the stimuli-responsive resonance variation, these D-r-D molecules exhibit extraordinary bipolar properties by positively charging one donor of carbazole in enantiotropic N+=P-X- canonical forms for electron transport without the involvement of any acceptors. With thus realized efficient and balanced charge transport, blue and deep-blue phosphorescent organic light emitting diodes hosted by these D-r-D molecules show high external quantum efficiencies up to 16.2% and 18.3% in vacuum-deposited and spin-coated devices, respectively. These results via the D-r-D molecular design strategy represent an important concept advance in constructing bipolar organic optoelectronic semiconductors dynamically for high-performance device applications

Flexible phosphorus doped carbon nanosheets/nanofibers : electrospun preparation and enhanced Li-storage properties as free-standing anodes for lithium ion batteries

The emerging wearable and foldable electronic devices drive the development of flexible lithium ion batteries (LIBs). Carbon materials are considered as one of the most promising electrode materials for LIBs due to their light weight, low cost and good structural stability against repeated deformations. However, the specific capacity, rate capability and long-term cycling performance still need to be improved for their applications in next-generation LIBs. Herein, we report a facile approach for immobilizing phosphorus into a large-area carbon nanosheets/nanofibers interwoven free-standing paper for LIBs. As an anode material for LIBs, it shows high reversible capacity of 1100 mAh g-1 at a current density of 200 mA g-1, excellent rate capabilities (e.g., 200 mAh g-1 at 20,000 mA g-1). Even at a high current density of 1000 mA g-1, it still maintains a superior specific capacity of 607 mAh g-1 without obvious decay

N‑Heterocyclic Carbene-Catalyzed Formal [3+2] Annulation of Alkynyl Aldehydes with Nitrosobenzenes: A Highly Regioselective Umpolung Strategy

N-Heterocyclic carbene-catalyzed formal [3+2] annulation of alkynyl aldehydes and nitrosobenzenes has been reported. This transformation provided the novel C–X bond formation under mild conditions in moderate to satisfactory yields. The catalytic protocol allows for a rapid construction of 2,5-disubstituted isoxazol-3­(2H)-ones and 2,3-disubstituted isoxazol-5­(2H)-ones from the same materials via a highly regioselectively umpolung stratgy

N‑Heterocyclic Carbene-Catalyzed Formal [3+2] Annulation of Alkynyl Aldehydes with Nitrosobenzenes: A Highly Regioselective Umpolung Strategy

N-Heterocyclic carbene-catalyzed formal [3+2] annulation of alkynyl aldehydes and nitrosobenzenes has been reported. This transformation provided the novel C–X bond formation under mild conditions in moderate to satisfactory yields. The catalytic protocol allows for a rapid construction of 2,5-disubstituted isoxazol-3­(2H)-ones and 2,3-disubstituted isoxazol-5­(2H)-ones from the same materials via a highly regioselectively umpolung stratgy

Direct Population of Triplet States for Efficient Organic Afterglow through the Intra/Intermolecular Heavy-Atom Effect

Organic afterglow is a fascinating phenomenon with exceptional applications. However, it encounters challenges such as low intensity and efficiency, and typically requires UV-light excitation and facile intersystem crossing (ISC) due to its spin-forbidden nature. Here, we develop a novel strategy that bypasses the conventional ISC pathway by promoting singlet-triplet transition through the synergistic effects of the intra/intermolecular heavy-atom effect in aromatic crystals, enabling the direct population of triplet excited states from the ground state. The resulting materials exhibit a bright organic afterglow with a remarkably enhanced quantum efficiency of up to 5.81%, and a significantly increased organic afterglow lifetime of up to 157 microseconds under visible light. Moreover, given the high-efficiency visible-light excitable organic afterglow emission, the potential application is demonstrated in lifetime-resolved, color-encoded, and excitation wavelength-dependent pattern encryption. This work demonstrates the importance of the direct population method in enhancing the organic afterglow performance and red-shifting the excitation wavelength, and provides crucial insights for advancing organic optoelectronic technologies that involve triplet states

Instantaneous ballistic velocity of suspended Brownian nanocrystals measured by upconversion nanothermometry

Brownian motion is one of the most fascinating phenomena in nature(1,2). Its conceptual implications have a profound impact in almost every field of science and even economics, from dissipative processes in thermodynamic systems(3,4), gene therapy in biomedical research(5), artificial motors(6) and galaxy formation(7) to the behaviour of stock prices(8). However, despite extensive experimental investigations, the basic microscopic knowledge of prototypical systems such as colloidal particles in a fluid is still far from being complete. This is particularly the case for the measurement of the particles' instantaneous velocities, elusive due to the rapid random movements on extremely short timescales(9). Here, we report the measurement of the instantaneous ballistic velocity of Brownian nanocrystals suspended in both aqueous and organic solvents. To achieve this, we develop a technique based on upconversion nanothermometry. We find that the population of excited electronic states in NaYF4: Yb/Er nanocrystals at thermal equilibrium can be used for temperature mapping of the nanofluid with great thermal sensitivity (1.15% K-1 at 296 K) and a high spatial resolution (< 1 mu m). A distinct correlation between the heat flux in the nanofluid and the temporal evolution of Er3+ emission allows us to measure the instantaneous velocity of nanocrystals with different sizes and shapes

Templating C₆₀ on MoS₂ Nanosheets for 2D Hybrid van der Waals <i>p</i>–<i>n</i> Nanoheterojunctions

C₆₀ and single-layer MoS₂ nanocomposites were facilely prepared via a combined solvent transfer and surface deposition (STSD) method by templating C₆₀ aggregates on 2D MoS₂ nanosheets to construct hybrid van der Waals heterojunctions. The electronic property of the hybrid nanomaterials was investigated in a direct charge transport diode device configuration of ITO/C₆₀–MoS₂ nanocomposites/Al; rewritable nonvolatile resistive switching with low SET/RESET voltage (∼3 V), high ON/OFF resistance ratio (∼4 × 10³), and superior electrical bistability (>10⁴ s) of a flash memory behavior was observed. This particular electrical property of C₆₀–MoS₂ nanocomposites, not possessed by either C₆₀ or MoS₂ nanosheets, was supposed to be due to the efficiently established C₆₀/MoS₂ <i>p</i>–<i>n</i> nanojunction, which controls the electron tunneling via junction barriers modulated by electric-field-induced polarization. Thus, our 2D templating method through STSD is promising to massively allocate van der Waals <i>p</i>–<i>n</i> heterojunctions in 2D nanocomposites, opening a window for important insights into the charge transport across the interface of organic/2D-semiconductors