A series of blue-emissive 7-(diphenylamino)-4-phenoxycoumarin derivatives bearing -CF , -OMe, or -N(Me) substituents on the phenoxy subunit were synthesized. Although both the -CF and -N(Me) modifications were found to trigger redshifted fluorescence, the -OMe substitution was demonstrated to exert an unexpected blueshift color-tuning effect toward the deep-blue region. The reason is that the moderate electron-donating -OMe group can endow coumarins with unaltered HOMO but elevated LUMO energy levels. Moreover, the -OMe substitution was found to be beneficial to the thermal stability of these coumarins. Therefore, the trimethoxy-substituted objective compound can act as a high-performance deep-blue organic light-emitting diode (OLED) emitter, and OLED based on it emits deep-blue light with CIE coordinates of (0.148, 0.084), maximum luminance of 7800 cd m , and maximum external quantum efficiency of 5.1 %. These results not only shed light on the molecular design strategy for high-performance deep-blue OLED emitters through color-tuning, but also show the perspective of coumarin derivatives as deep-blue OLED emitters.
Spiroacetal moieties containing linear telechelic polymers (LTPs) with two terminal epoxy groups were facilely synthesized via the successive thiol‐ene and thiol‐epoxy click additions. The LTPs were incorporated into epoxy matrix to fabricate the transparent and toughening thermosets. In term of the miscibility of epoxy with the adduct of ethanedithiol and 3,9‐divinyl‐2,4,8,10‐tetraoxaspiro[5.5]undecane (BTU), it is proposed that the size of the formed nanostructures was small enough to allow light penetrate. Therefore, the modified thermosets were transparent, which was further confirmed by small‐angle X‐ray scattering (SAXS) measurements. The LTPs with an alternating structure of rigid spiroacetal moiety and soft thioether could formed heterogeneous crosslinked networks (HCNs) and obviously toughen epoxy thermosets. Flexural strength increased from 1.06 GPa for neat epoxy to 2.09 GPa for toughening thermosets modified with 15 wt% LTPs. The stress field intensity (KIC) value reached up to 3.93 by more than 125% compared with that of the control sample (1.75). This work uncovered the role of HCNs on performance and paved a way for technological advances toward transparent and toughening materials in epoxy thermosets.
The rise of government micro-blogs opens a new era for the interaction between the government and the public. As critical stakeholders, the public's opinions on the operation of government micro-blogs are important for their future improvement. In order to explore the public's expectations on government micro-blogs, contents of public micro-blogs on government micro-blogs were collected and analyzed by adopting a grounded theory approach. A conceptual model of the public's expectation on government micro-blogs was generated and its policy implications were discussed. According to the model, a government micro-blog should clearly define its target, strengthen its functions, normalize its business process, and improve its maintenance and management in order to increase its service quality. Furthermore, improving the quality of information openness, strengthening interactions with the public, and advancing the capability of solving practical problems were found to be the three specific developmental orientations of government micro-blogs in the future.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.