Zhongfu An

Remote C−H Activation of Quinolines through Copper‐Catalyzed Radical Cross‐Coupling

Achieving site selectivity in carbon-hydrogen (C-H) functionalization reactions is a formidable challenge in organic chemistry. Herein, we report a novel approach to activating remote C-H bonds at the C5 position of 8-aminoquinoline through copper-catalyzed sulfonylation under mild conditions. Our strategy shows high conversion efficiency, a broad substrate scope, and good toleration with different functional groups. Furthermore, our mechanistic investigations suggest that a single-electron-transfer process plays a vital role in generating sulfonyl radicals and subsequently initiating C-S cross-coupling. Importantly, our copper-catalyzed remote functionalization protocol can be expanded for the construction of a variety of chemical bonds, including C-O, C-Br, C-N, C-C, and C-I. These findings provide a fundamental insight into the activation of remote C-H bonds, while offering new possibilities for rational design of drug molecules and optoelectronic materials requiring specific modification of functional groups.

Multicolour synthesis in lanthanide-doped nanocrystals through cation exchange in water

Meeting the high demand for lanthanide-doped luminescent nanocrystals across a broad range of fields hinges upon the development of a robust synthetic protocol that provides rapid, just-in-time nanocrystal preparation. However, to date, almost all lanthanide-doped luminescent nanomaterials have relied on direct synthesis requiring stringent controls over crystal nucleation and growth at elevated temperatures. Here we demonstrate the use of a cation exchange strategy for expeditiously accessing large classes of such nanocrystals. By combining the process of cation exchange with energy migration, the luminescence properties of the nanocrystals can be easily tuned while preserving the size, morphology and crystal phase of the initial nanocrystal template. This post-synthesis strategy enables us to achieve upconversion luminescence in Ce3+ and Mn2+-activated hexagonal-phased nanocrystals, opening a gateway towards applications ranging from chemical sensing to anti-counterfeiting.

Conjugated Asymmetric Donor‐Substituted 1,3,5‐Triazines: New Host Materials for Blue Phosphorescent Organic Light‐Emitting Diodes

Conjugated asymmetric donor-substituted 1,3,5-triazines (ADTs) have been synthesized by nucleophilic substitution of organolithium catalyzed by [Pd(PPh(3))(4)]. Theoretical and experimental investigations show that ADTs possess high solubility and thermostability, high fluorescent quantum yield (35%), low HOMO (-6.0 eV) and LUMO (-2.8 eV), and high triplet energy (E(T), 3.0 eV) according to the different substitution pattern of triazine. The application as host materials for blue PHOLEDs yielded a maximum current efficiency of 20.9 cd A(-1), a maximum external quantum efficiency of 9.8%, and a brightness of 9671 cd m(-2) at 5.4 V, making ADTs good candidates for optoelectronic devices.

Dynamically Adaptive Characteristics of Resonance Variation for Selectively Enhancing Electrical Performance of Organic Semiconductors

Increased resonance: The selective tuning of the optoelectronic properties of organic semiconductors is possible by enantiotropic resonance variation. Using resonance forms of N(+)=P-O(-) in a series of arylamine-phosphine oxide hybrids afforded low-voltage-driven phosphorescent OLEDs with outstanding performances.

Exceptional Blueshifted and Enhanced Aggregation‐Induced Emission of Conjugated Asymmetric Triazines and Their Applications in Superamplified Detection of Explosives

A novel conjugated asymmetric donor-acceptor (CADA) strategy for preventing the redshift in photoluminescence, as well as preserving the merits of donor-acceptor architectures, was proposed and demonstrated for two triazine derivatives, which showed highly efficient, narrow, and blueshifted ultraviolet light emission in solid films along with special aggregation-induced emission behavior. A mechanism of aggregation-induced locally excited-state emission by suppressing the twisted intramolecular charge-transfer emission for the spectacular optoelectronic phenomena of these CADA molecules was suggested on the basis of both experimental measurements and theoretical calculations. By taking advantage of this special CADA architecture, fluorescent probes based on aggregates of conjugated asymmetric triazines in THF/water for the detection of explosives show superamplified detection of picric acid with high quenching constants (>1.0 × 10(7) M(-1)) and a low detection limit of 15 ppb.

Understanding the Control of Singlet-Triplet Splitting for Organic Exciton Manipulating: A Combined Theoretical and Experimental Approach

Developing organic optoelectronic materials with desired photophysical properties has always been at the forefront of organic electronics. The variation of singlet-triplet splitting (ΔEST) can provide useful means in modulating organic excitons for diversified photophysical phenomena, but controlling ΔEST in a desired manner within a large tuning scope remains a daunting challenge. Here, we demonstrate a convenient and quantitative approach to relate ΔEST to the frontier orbital overlap and separation distance via a set of newly developed parameters using natural transition orbital analysis to consider whole pictures of electron transitions for both the lowest singlet (S1) and triplet (T1) excited states. These critical parameters revealed that both separated S1 and T1 states leads to ultralow ΔEST; separated S1 and overlapped T1 states results in small ΔEST; and both overlapped S1 and T1 states induces large ΔEST. Importantly, we realized a widely-tuned ΔEST in a range from ultralow (0.0003 eV) to extra-large (1.47 eV) via a subtle symmetric control of triazine molecules, based on time-dependent density functional theory calculations combined with experimental explorations. These findings provide keen insights into ΔEST control for feasible excited state tuning, offering valuable guidelines for the construction of molecules with desired optoelectronic properties.

Single‐Layer Transition Metal Dichalcogenide Nanosheet‐Assisted Assembly of Aggregation‐Induced Emission Molecules to Form Organic Nanosheets with Enhanced Fluorescence

Single-layer transition metal dichalcogenide nanosheets including MoS2, TiS2 and TaS2 can be used as novel platforms for the fluorescence enhancement of aggregation-induced emission fluorophores. The small organic AIE unit can be assembled into a two-dimensional sheet structure via a simple precipitation technique assisted by these monolayers. The resultant organic sheets possess a size of 0.2-2 μm and a thickness of 9-20 nm.

Hyper-Branched Phosphorescent Conjugated Polyelectrolytes for Time-Resolved Heparin Sensing

A series of hyper-branched cationic conjugated polyelectrolytes containing different contents of phosphorescent Ir(III) complex has been designed and synthesized successfully. Their photophysical properties in both aqueous solution and solid film are investigated and their morphologies in aqueous solution are observed by TEM. Nanoparticles with the size of 80-100 nm have been formed in aqueous solution through the self-assembly of polymers. An energy transfer process from host polyfluorene to guest Ir(III) complex exists and becomes more efficient in the solid films. Importantly, this series of hyper-branched polymers can be applied as light-up heparin probes with good selectivity, high sensitivity, and naked-eye detection through electrostatic interaction between polymers and heparin. Quantification for heparin in aqueous solution can be realized in the range of 0-44 μM in the buffer solution. Detection limit can reach as low as 50 nM. More meaningfully, time-resolved photoluminescence technique is utilized successfully in the heparin sensing to eliminate the background fluorescence interference effectively and enhance the sensing sensitivity in the complicated media.

Visible-Light-Excited Ultralong Organic Phosphorescence by Manipulating Intermolecular Interactions

Visible light is much more available and less harmful than ultraviolet light, but ultralong organic phosphorescence (UOP) with visible-light excitation remains a formidable challenge. Here, a concise chemical approach is provided to obtain bright UOP by tuning the molecular packing in the solid state under irradiation of available visible light, e.g., a cell phone flashlight under ambient conditions (room temperature and in air). The excitation spectra exhibit an obvious redshift via the incorporation of halogen atoms to tune intermolecular interactions. UOP is achieved through H-aggregation to stabilize the excited triplet state, with a high phosphorescence efficiency of 8.3% and a considerably long lifetime of 0.84 s. Within a brightness of 0.32 mcd m-2 that can be recognized by the naked eye, UOP can last for 104 s in total. Given these features, ultralong organic phosphorescent materials are used to successfully realize dual data encryption and decryption. Moreover, well-dispersed UOP nanoparticles are prepared by polymer-matrix encapsulation in an aqueous solution, and their applications in bioimaging are tentatively being studied. This result will pave the way toward expanding metal-free organic phosphorescent materials and their applications.

Computational design and selection of optimal building blocks and linking topologies for construction of high-performance host materials

Two typical hole transport groups, carbazole and diphenylamine, and two typical electron transport groups, diphenylphosphine oxide and triphenylsilane, were linked to biphenyl at its ortho/meta/para-positions to investigate the effects of building blocks and linking topologies on the structural and electronic properties of such constructed host materials via density function theory calculation. It is found that the frontier orbital levels, energy band gap, and triplet energy of host molecules can be effectively tuned by different building blocks and linking topologies. The electron-transporting nature of π-conjugated molecules can be enhanced by connecting electron-withdrawing building blocks at the ortho or meta position, but not at the para-position. Employing asymmetric building blocks with meta-type topology would be an effective strategy for the design of high-performance bipolar host materials.