The development of high-performance near-infrared organic light-emitting diodes is hindered by strong non-radiative processes as governed by the energy gap law. Here, we show that exciton ...delocalization, which serves to decouple the exciton band from highly vibrational ladders in the S0 ground state, can bring substantial enhancements in the photoluminescence quantum yield of emitters, bypassing the energy gap law. Experimental proof is provided by the design and synthesis of a series of new Pt(ii) complexes with a delocalization length of 5–9 molecules that emit at 866–960 nm with a photoluminescence quantum yield of 5–12% in solid films. The corresponding near-infrared organic light-emitting diodes emit light with a 930 nm peak wavelength and a high external quantum efficiency up to 2.14% and a radiance of 41.6 W sr−1 m−2. Both theoretical and experimental results confirm the exciton–vibration decoupling strategy, which should be broadly applicable to other well-aligned molecular solids.Pt(ii) complexes allow the fabrication of efficient near-infrared organic light-emitting diodes that operate beyond the 900 nm region.
Although augmented reality (AR) has gained much research attention in recent years, the term AR was given different meanings by varying researchers. In this article, we first provide an overview of ...definitions, taxonomies, and technologies of AR. We argue that viewing AR as a concept rather than a type of technology would be more productive for educators, researchers, and designers. Then we identify certain features and affordances of AR systems and applications. Yet, these compelling features may not be unique to AR applications and can be found in other technological systems or learning environments (e.g., ubiquitous and mobile learning environments). The instructional approach adopted by an AR system and the alignment among technology design, instructional approach, and learning experiences may be more important. Thus, we classify three categories of instructional approaches that emphasize the “roles,” “tasks,” and “locations,” and discuss what and how different categories of AR approaches may help students learn. While AR offers new learning opportunities, it also creates new challenges for educators. We outline technological, pedagogical, learning issues related to the implementation of AR in education. For example, students in AR environments may be cognitively overloaded by the large amount of information they encounter, the multiple technological devices they are required to use, and the complex tasks they have to complete. This article provides possible solutions for some of the challenges and suggests topics and issues for future research.
► We argue that viewing AR as a concept rather than a technology is more productive. ► We identify features and affordances of AR systems and applications. ► The instructional approaches adopted by an AR system are discussed. ► While AR offers new learning opportunities, it also creates new challenges. ► We provide solutions for challenges and suggest directions for future research.
Finding a relationship between kinetics and thermodynamics may be difficult. However, semi‐empirical rules exist to compensate for this shortcoming, among which the Bell–Evans–Polanyi (B‐E‐P) ...principle is an example for reactions involving bond breakage and reformation. We expand the B‐E‐P principle to a new territory by probing photoinduced structure planarization (PISP) of a series of dibenzb,fazepine derivatives incorporating bent‐to‐planar and rotation motion. The latter involves twisting of the partial double bond character, thereby inducing a barrier that is substituent dependent at the para N‐phenyl position. The transition‐state structure and frequency data satisfy and broaden the B‐E‐P principle to PISP reactions without bond rearrangement. Together with dual emissions during PISP, this makes possible harnessing of the kinetics/thermodynamics relationship and hence ratiometric luminescence properties for excited‐state structural transformations.
The Bell–Evans–Polanyi principle was used to probe photoinduced structure planarization of a series of dibenzb,fazepine (DBA) derivatives incorporating bent‐to‐planar and rotation motion. A saddle point was calculated for all PDBAs along the structural transition pathway. A relationship was elucidated between kinetics and thermodynamics, providing insight into the ratiometric luminescence properties of excited‐state structural transformations.
To combat hostile viruses, bacteria and archaea have evolved a unique antiviral defense system composed of clustered regularly interspaced short palindromic repeats (CRISPRs), together with ...CRISPR-associated genes (Cas). The CRISPR/Cas9 system develops an adaptive immune resistance to foreign plasmids and viruses by creating site-specific DNA double-stranded breaks (DSBs). Here we adapt the CRISPR/Cas9 system to human cells for intracellular defense against foreign DNA and viruses. Using HIV-1 infection as a model, our results demonstrate that the CRISPR/Cas9 system disrupts latently integrated viral genome and provides long-term adaptive defense against new viral infection, expression and replication in human cells. We show that engineered human-induced pluripotent stem cells stably expressing HIV-targeted CRISPR/Cas9 can be efficiently differentiated into HIV reservoir cell types and maintain their resistance to HIV-1 challenge. These results unveil the potential of the CRISPR/Cas9 system as a new therapeutic strategy against viral infections.
We propose a new concept exploiting thermally activated delayed fluorescence (TADF) molecules as photosensitizers, storage units and signal transducers to harness solar thermal energy. Molecular ...composites based on the TADF core phenoxazine-triphenyltriazine (PXZ-TRZ) anchored with norbornadiene (NBD) were synthesized, yielding compounds PZDN and PZTN with two and four NBD units, respectively. Upon visible-light excitation, energy transfer to the triplet state of NBD occurred, followed by NBD → quadricyclane (QC) conversion, which can be monitored by changes in steady-state or time-resolved spectra. The small S
-T
energy gap was found to be advantageous in optimizing the solar excitation wavelength. Upon tuning the molecule's triplet state energy lower than that of NBD (61 kcal/mol), as achieved by another composite PZQN, the efficiency of the NBD → QC conversion decreased drastically. Upon catalysis, the reverse QC → NBD reaction occurred at room temperature, converting the stored chemical energy back to heat with excellent reversibility.
We demonstrate directed translocation of ClO4− anions from cationic to neutral binding site along the synthetized BPym‐OH dye molecule that exhibits coupled excited‐state intramolecular ...proton‐transfer (ESIPT) and charge‐transfer (CT) reaction (PCCT). The results of steady‐state and time‐resolved spectroscopy together with computer simulation and modeling show that in low polar toluene the excited‐state redistribution of electronic charge enhanced by ESIPT generates the driving force, which is much stronger than by CT reaction itself and provides more informative gigantic shifts of fluorescence spectra signaling on ultrafast ion motion. The associated with ion translocation red‐shifted fluorescence band (at 750 nm, extending to near‐IR region) appears at the time ~83 ps as a result of electrochromic modulation of PCCT reaction. It occurs at substantial delay to PCCT that displayed fluorescence band at 640 nm and risetime of <200 fs. Thus, it becomes possible to visualize the manifestations of light‐triggered ion translocation and of its driving force by fluorescence techniques and to separate them in time and energy domains.
The light‐triggered translocation of ClO4− anion from cationic to neutral‐binding site along BPym‐OH dye is visualized by emission. The combination of time‐resolved fluorescence and molecular dynamic simulation allows its description in time and energy domains. This reaction generates dramatically red‐shifted fluorescence extending to near‐IR that appears at ~83 ps, resulting from electrochromic modulation of coupled proton‐electron transfer.
In sharp contrast to most photoinduced structural planarization (PISP) phenomena, which are highly exergonic and irreversible processes, we report here a series of a new class of PISP molecules, ...9-phenyl-9H-tribenzob,d,fazepine (PTBA) and its derivatives, where PISP is within the thermally reversible regime. The underlying foundation is the energy counterbalance along PISP, where upon electronic excitation the azepine core chromophore undergoes planarization to gain stabilization from a cyclic 4n π conjugation (n is an integer; Baird’s rule). Concurrently, the C7C8 fused benzene ring is prone to gain aromaticity, which conversely decreases the 4n π-electron resonance stabilization of the 9H-tribenzob,d,fazepine, hindering a full planarization. The offset results in a minimum energy state (P*) along PISP that is in thermal equilibrium with the initially prepared state (R*). The relaxed structure of R* deviates greatly from the planar configuration commonly seen in PISP. PISP of PTBAs is thus sensitive to the solvent polarity, temperature, and substituents, causing prominent stimuli-dependent ratiometric fluorescence for R* versus P*. Exploitation of the energy counterbalance effect proves to be a practical strategy for harnessing excited-state structural relaxation.
Herein, we applied PmST1 (a sialyltransferase) to achieve acceptor-mediated regioselective sialylation (AMRS) on the nonreducing end GalNH
2
or GalAz (2-azido-2-deoxy galactose). Thus, C5 and ...C8-modified sialic acid was efficiently assembled on GalNH
2
(or GalAz) to achieve the synthesis of the GAA-7 (one of the echinodermatous gangliosides with higher neuritogenic activity) glycan moiety.
The glycan of GAA-7 was facilely synthesized by enzymatic glycosylation through changing the nonreducing acceptor into GalNH
2
or GalAz to successfully switch the regioselectivity of PmST1.
T-cell acute lymphoblastic leukemia (T-ALL) is caused by the accumulation of multiple genetic alterations. To determine the frequency of common genetic mutations and possible prognostic markers in ...childhood T-ALL, we performed targeted sequencing of 67 genes across 64 cases treated according to Taiwan Pediatric Oncology Group protocols between January 2002 and December 2015. Together, 302 variants were identified in 60 genes including 233 single nucleotide variants and 69 indels. Sixty-four samples had a median number of six genetic lesions each (range 1-17). Thirteen genes had mutation frequencies > 10%, and 5 were > 20%, with the highest being NOTCH1 (70.31%). Protocadherins FAT1 (32.81%) and FAT3 (17.19%), and the ubiquitin ligase component FBXW7 (28.13%) had higher mutation frequencies than previously reported. Other mutation frequencies (PHF6, DNM2, DNMT3A, CNOT3, and WT1) were within previously reported ranges. Three epigenetic-related genes (KMT2D, DNMT3A, and EZH2) were mutated in our cohort. JAK-STAT signaling pathway genes had mutation frequencies of 3-13% and were observed in 23 cases (35.94%). Changes to genes in the ErbB signaling pathway were detected in 20 cases (31.25%). Patients with NOTCH1/FBXW7 mutations and RAS/PTEN germline exhibited better 5-year overall survival rates.
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