High-performance deep-blue emitting phenanthroimidazole derivatives with a structure of donor−linker−acceptor were designed and synthesized. By using different linkers and different linking positions, four deep-blue emitters were obtained and used as emitters or bifunctional hole-transporting emitters in OLEDs. Such devices show low turn-on voltages (as low as 2.8 V), high efficiency (2.63 cd/A, 2.53 lm/W, 3.08%), little efficiency roll-off at high current densities, and stable deepblue emissions with CIE y < 0.10. Performances are among the best comparing to recently reported deep-blue emitting devices with similar structures. The results suggest that the combination of the phenanthroimidazole and the donor−linker− acceptor structure can be an important approach for developing high performance deep-blue emitters in particular for lighting applications.

Two series of new tetracyclic pyrazolo[3,4-b]pyridine-based coumarin chromophores were synthesized through a facile reaction between 3-aldehyde-7-diethylaminocoumarin (5) or 3-acetyl-7-diethylaminocoumarin (6) and 5-aminopyrazole derivatives (7) in a one-pot procedure. Different condensed products were obtained from compounds 5 and 6, and the potential reaction mechanism was studied using the reaction of 5 with 5-amino-1-phenylpyrazole (7a). The molecular structures were characterized by NMR and HRMS and confirmed by X-ray diffraction. The photophysical, electrochemical, and thermal properties of these compounds were investigated by absorption spectroscopy, fluorescence spectroscopy, single photon counting technique, cyclic voltammetry, thermogravimetric analysis, etc. Results show that the compounds exhibited high fluorescence quantum yields and good electrochemical, thermal, and photochemical stabilities. In addition, the application of these highly fluorescent compounds in living cell imaging was also explored by laser scanning confocal microscopy.

A new series of intramolecular charge transfer (ICT) molecules were synthesized by attaching various strong electron-withdrawing groups to a triphenylamine backbone. Relationships between chemical structures and optoelectronic properties of these compounds were investigated with X-ray diffraction, cyclic voltammetry, absorption spectroscopy, and density functional theory calculations. It is shown that the compounds exhibit intensive ICT interactions leading to substantial extension of their absorption spectral response, which may be potentially used for efficient solar cells.

Infrared camouflage is crucial for high-temperature objects to avoid detection, and spontaneous infrared radiation is also an important way for high-temperature objects to dissipate heat. Therefore, selective infrared emission has become significant for the coating design of surfaces such as aircraft, which require low emission in the atmospheric window band (3–5 µm and 8–14 µm) and high emission outside it (5–8 µm). This Letter employs a simple multilayer film structure to achieve selective regulation of the material emission spectrum. Combining the transfer matrix method and genetic algorithm, a multilayer film structure containing 12 layers of three high-temperature-resistant materials ( S i O 2 , T i O 2 and Ge) has been designed. It shows fairly low emissivity in two main bands of infrared detection ( ε 3 ∼ 5 µ m = 0.14 , ε 8 ∼ 14 µ m = 0.21 ) and high emissivity outside them ( ε 5 ∼ 8 µ m = 0.86 ), and this infrared selectivity can be well maintained with the incident angle rising from 0 to 60 deg. The Poynting vector distribution in the material at different incident wavelengths is analyzed to further explore the interference mechanism to achieve spectral selective emission. The significance of this work lies in the construction of a relatively simple coating design while ensuring efficient infrared camouflage and thermal management performance.

No abstract

In this paper, we have theoretically demonstrated a graphene-mediated near-field radiative thermal modulator based on doped silicon-graphene-doped silicon three-slab configuration. The near-field photon tunneling between the doped silicon emitter and receiver is modulated by changing chemical potential of graphene sheet and the separation distance between the sheet and the emitter. The near-field three-body theory built on fluctuational electrodynamics is used to calculate total radiative heat flux, which could be modulated in a range of 10-70 kW/m 2 with different setup for graphene chemical potential and its position. The underlying mechanism is illustrated as varied coupling behavior of surface plasmon polaritons between doped silicon and graphene sheet. Several dimensionless factors such as normalized heat flux, sensitivity factor and switching factor are also introduced for comprehensive analysis of the performance of modulation effect. The results obtained here will trigger a new way for near-field active thermal management between bulk materials utilizing suspended 2-D materials.

No abstract

No abstract