Huili Ma

White light emission from a single organic molecule with dual phosphorescence at room temperature

The development of single molecule white light emitters is extremely challenging for pure phosphorescent metal-free system at room temperature. Here we report a single pure organic phosphor, namely 4-chlorobenzoyldibenzothiophene, emitting white room temperature phosphorescence with Commission Internationale de l’Éclair-age coordinates of (0.33, 0.35). Experimental and theoretical investigations reveal that the white light emission is emerged from dual phosphorescence, which emit from the first and second excited triplet states. We also demonstrate the validity of the strategy to achieve metal-free pure phosphorescent single molecule white light emitters by intrasystem mixing dual room temperature phosphorescence arising from the low- and high-lying triplet states.The development of single molecule white light-emitters is extremely challenging for pure phosphorescent metal-free systems at room temperature. Here the authors show a single pure organic room temperature phosphor, 4-chlorobenzoyldibenzothiophene, utilizing the emission from both T1 and T2 states.

Electrostatic Interaction-Induced Room-Temperature Phosphorescence in Pure Organic Molecules from QM/MM Calculations

Room temperature phosphorescence (RTP) from pure organic material is rare due to the low phosphorescence quantum efficiency. That is why the recent discovery of crystallization induced RTP for several organic molecules aroused strong interests. Through a combined quantum and molecular mechanics CASPT2/AMBER scheme taking terephthalic acid (TPA) as example, we found that electrostatic interaction not only can induce an enhanced radiative decay T1 → S0 through the dipole-allowed S1 intermediate state, but also can hinder the nonradiative decay process upon crystallization. From gas phase to crystal, the nature of S1 state is converted to (1)(π,π*) from (1)(n,π*) character, enhancing transition dipole moment and serving as an efficient intermediate radiative pathway for T1 → S0 transition, and eventually leading to a boosted RTP. The intermolecular packing also blocks the nonradiative decay channel of the high-frequency C═O stretching vibration with large vibronic coupling, rather than the conventional low-frequency aromatic rotation in crystal. This mechanism also holds for other organic compounds that contain both ketones and aromatic rings.

Ultralong Phosphorescence from Organic Ionic Crystals under Ambient Conditions

A new type of materials, organic salts in the crystal state, have ultralong organic phosphorescence (UOP) under ambient conditions. The change of cations (NH4+ , Na+ , or K+ ) in these phosphors gives access to tunable UOP colors ranging from sky blue to yellow green, along with ultralong emission lifetimes of over 504u2005ms. Single-crystal analysis reveals that unique ionic bonding can promote an ordered arrangement of organic salts in crystal state, which then can facilitate molecular aggregation for UOP generation. Additionally, reversible ultralong phosphorescence can be realized through the alternative employment of fuming gases (ammonia and hydrogen chloride), demonstrating its potential as a candidate for visual ammonic or hydrogen chloride gas sensing. The results provide an environmental responsible and practicable synthetic approach to expanding the scope of ultralong organic phosphorescent materials as well as their applications.

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 79.8u2005ms 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.

Wear resistance of Fe-based amorphous coatings prepared by AC-HVAF and HVOF

Fe63Cr8Mo3.5Ni5P10B4C4Si2.5 amorphous coatings have been prepared by the activated combustion high velocity air fuel (AC-HVAF) and high velocity oxygen fuel (HVOF) processes. The microstructure and wear resistance of the amorphous coatings are comparatively studied. The wear volume loss of the AC-HVAF coating is approximately seven times less than that of the HVOF coating, indicating that the AC-HVAF coating exhibits better wear resistance. Detailed analysis on the worn surface indicates that the enhanced wear resistance of the AC-HVAF coating is mainly attributed to the formation of a more stable oxide tribolayer and smoother worn surface, which result from the dense and complete amorphous microstructure of the AC-HVAF coating. The wear mechanism of the amorphous coatings is dominated by oxidation wear.

Highly sensitive switching of solid-state luminescence by controlling intersystem crossing

The development of intelligent materials, in particular those showing the highly sensitive mechanoresponsive luminescence (MRL), is desirable but challenging. Here we report a design strategy for constructing high performance On–Off MRL materials by introducing nitrophenyl groups to molecules with aggregation-induced emission (AIE) characteristic. The on–off methodology employed is based on the control of the intersystem crossing (ISC) process. Experimental and theoretical investigations reveal that the nitrophenyl group effectively opens the nonradiative ISC channel to impart the high sensitivity and contrast On–Off behavior. On the other hand, the twisted AIE luminogen core endows enhanced reversibility and reduces the pressure required for the luminescence switching. Thinxa0films can be readily fabricated from the designed materials to allow versatile applications in optical information recording and haptic sensing. The proposed design strategy thus provides a big step to expand the scope of the unique On–Off MRL family.The development of intelligent materials, in particular those showing the highly sensitive mechanoresponsive luminescence (MRL), remains challenging. Here the authors report a strategy for constructing high performance On-Off MRL materials by introducing nitrophenyl groups to molecules with aggregation-induced emission characteristic.

Corannulene‐Incorporated AIE Nanodots with Highly Suppressed Nonradiative Decay for Boosted Cancer Phototheranostics In Vivo

Fluorescent nanoparticles (NPs) based on luminogens with aggregation-induced emission characteristic (AIEgens), namely AIE dots, have received wide attention because of their antiquenching attitude in emission and reactive oxygen species (ROS) generation when aggregated. However, few reports are available on how to control and optimize their fluorescence and ROS generation ability. Herein, it is reported that enhancing the intraparticle confined microenvironment is an effective approach to advanced AIE dots, permitting boosted cancer phototheranostics in vivo. Formulation of a rotor-rich and inherently charged near-infrared (NIR) AIEgen with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] and corannulene-decorated PEG affords DSPE-AIE dots and Cor-AIE dots, respectively. Compared to DSPE-AIE dots, Cor-AIE dots show 4.0-fold amplified fluorescence quantum yield and 5.4-fold enhanced ROS production, because corannulene provides intraparticle rigidity and strong interactions with the AIEgen to restrict the intramolecular rotation of AIEgen to strongly suppress the nonradiative decay and significantly facilitate the fluorescence pathway and intersystem crossing. Thus, it tremendously promotes phototheranostic efficacies in terms of NIR image-guided cancer surgery and photodynamic therapy using a peritoneal carcinomatosis-bearing mouse model. Collectively, it not only provides a novel strategy to advanced AIE dots for cancer phototheranostics, but also brings new insights into the design of superior fluorescent NPs for biomedical applications.

Passivation Behavior of Fe-Based Amorphous Coatings Prepared by High-Velocity Air/Oxygen Fuel Processes

Abstract Corrosion resistance and passivation behavior of Fe63Cr8Mo3.5Ni5P10B4C4Si2.5 amorphous coatings prepared by the activated combustion high-velocity air fuel (AC-HVAF) and high-velocity oxygen fuel (HVOF) processes have been studied in detail by cyclic potentiodynamic polarization, electrochemical impedance spectroscopy, cathodic polarization and Mott–Schottky approach. The AC-HVAF coating shows higher corrosion resistance than the HVOF coating in 3.5xa0wt.% NaCl solution, as evidenced by its lower corrosion current density and passive current density. It is found that the superior corrosion resistance of the AC-HVAF coating is attributed to the enhanced formation of a dense passive film with less defective structure, higher pitting resistance and passivity stability, as well as stronger repassivity.

A facile strategy for realizing room temperature phosphorescence and single molecule white light emission

Research on materials with pure organic room temperature phosphorescence (RTP) and their application as organic single-molecule white light emitters is a hot area and relies on the design of highly efficient pure organic RTP luminogens. Herein, a facile strategy of heavy-atom-participated anion–π+ interactions is proposed to construct RTP-active organic salt compounds (1,2,3,4-tetraphenyloxazoliums with different counterions). Those compounds with heavy-atom counterions (bromide and iodide ions) exhibit outstanding RTP due to the external heavy atom effect via anion–π+ interactions, evidently supported by the single-crystal X-ray diffraction analysis and theoretical calculation. Their single-molecule white light emission is realized by tuning the degree of crystallization. Such white light emission also performs well in polymer matrices and their use in 3D printing is demonstrated by white light lampshades.The demonstration of pure organic room temperature phosphorescence (RTP) luminogens with complementary emission is a key requirement for developing low-cost white light emitters. Here, the authors construct RTP-active organic salt compounds by exchanging the counterion with a heavy halide ion.

Domino-like multi-emissions across red and near infrared from solid-state 2-/2,6-aryl substituted BODIPY dyes

Considerable achievements on multiple emission capabilities and tunable wavelengths have been obtained in inorganic luminescent materials. However, the development of organic counterparts remains a grand challenge. Herein we report a series of 2-/2,6-aryl substituted boron-dipyrromethene dyes with wide-range and multi-fluorescence emissions across red and near infrared in their aggregation states. Experimental data of X-ray diffraction, UV–vis absorption, and room temperature fluorescence spectra have proved the multiple excitation and easy-adjustable emission features in aggregated boron-dipyrromethene dyes. Temperature-dependent and time-resolved fluorescence studies have indicated a successive energy transfer from high to step-wisely lower-located energy levels that correspond to different excitation states of aggregates. Consistent quantum chemical calculation results have proposed possible aggregation modes of boron-dipyrromethene dyes to further support the above-described scenario. Thus, this study greatly enriches the fundamental recognition of conventional boron-dipyrromethene dyes by illustrating the relationships between multiple emission behaviors and the aggregation states of boron-dipyrromethene molecules.The class of BODIPY dyes has high solubility and high quantum yields and is widely used in imaging applications. Here Tian et al. synthesize new dye molecules and demonstrate extended emission properties and application scope controllable both by the excitation wavelength and aggregation states.