Effect of hybridized local and charge transfer molecules rotation in excited state on exciton utilization.

The fluorescent molecules utilizing hybridized local and charge-transfer (HLCT) state as potential organic light-emitting diodes materials attract extensive attention due to their high exciton utilization. In this work, we have performed the density functional theory method on three HLCT-state molecules to investigate their excited-state potential energy surface (PES). The calculated results indicate the T1 and T2 energy gap is quite large, and the T2 is very close to S1 in the energy level. The large gap is beneficial for inhibiting the internal conversion between T1 and T2, and quite closed S1 and T2 energies are favor for activating the T2 → S1 reverse intersystem crossing path. However, considering the singlet excited-state PES by twisting the triphenylamine (TPA) or diphenylamine (PA) group, it can be found that the TPA or PA group almost has no influence on T1 and T2 energy levels. However, the plots of S1 PES display two kinds of results that the S1 emissive state is dominated by charge-transfer (CT) or HLCT state. The CT emission state formation would decrease the S1 energy level, enlarge the S1 and T2 gap, and impair the triplet exciton utilization. Therefore, understanding the relationship between the S1 PES and molecular structures is important for designing high-performance luminescent materials utilizing HLCT state.

Hemispherical Cesium Lead Bromide Perovskite Single-Mode Microlasers with High-Quality Factors and Strong Purcell Enhancement.

We realized a single-mode laser with an ultra-high quality factor in individual cesium lead bromide (CsPbBr3) perovskite micro-hemispheres fabricated by chemical vapor deposition. A series of lasing property analysis based on cavity size was reported under this material system. Due to good optical confinement capability of the whispering gallery resonant cavity and high optical gain of CsPbBr3 perovskite micro-hemispheres, single-mode lasing behavior was achieved with an ultra-high quality factor as large as 11,460 at room temperature. To study in detail the physical effects between lasing threshold and cavity, a set of cavity size dependence photoluminescence analyses were performed. We found that the lasing threshold increases while the cavity size decreases. Time-resolved PL analysis was conducted to confirm the relation between cavity size and lasing threshold. The larger cavity stands for longer PL lifetime and indicates easier-to-achieve carrier population inversion. Strong Purcell enhancement could be further investigated by the spontaneous emission coupling factor ß and internal quantum efficiency as a function of cavity size. A high ß-factor of 0.37 could be obtained from a 2.2 µm diameter hemisphere microcavity and a high Purcell factor of 14 in a 1.9 µm diameter hemisphere microcavity showing strong Purcell enhancement effect in our system.

Size-Dependent Catalytic Activity of Oxo-Hydroxo Titanium Sub-Nanoislets Grafted on Organically Modified Mesoporous Silica.

The reaction between titanium alkoxides, [Ti(OR)4], and surface silanol groups is widely used to generate grafted oxo-hydroxo titanium species, whose size is difficult to control. Partial capping of the surface silanols in the presence of the masking pattern of self-repelling tetramethylammonium ions allows us to isolate surface silanol islets, on which isolated titanium ions and dimeric oxo titanium species can be generated up to 2 Ti/Si mol %. Above this loading, and up to ∼8 Ti/Si mol %, higher oligomers (trimers, hexamers, octamers, and so on) are formed, reaching the size obtained at much lower loadings (<1 Ti/Si mol %) on a nonmodified silica surface. The downsizing effect produced on our organically modified surface is monitored from the blue-shift of the charge-transfer band of the Ti(IV) ions, measured by reflectance UV-visible spectroscopy. It is also mirrored by a higher catalytic activity in cyclohexene epoxidation, revealing that it is not only the isolated Ti species that are active but also the oligomers. Regarding the latter, the smaller they are, the more active they are.

Synthesis of Extra-Large-Pore Zeolite ECNU-9 with Intersecting 14*12-Ring Channels.

Highly crystalline and (hydro)thermally stable zeolites with extra-large pores [≥14-ring (14-R)] are desirable as catalysts. A novel zeolite, ECNU-9, with an intersecting 14*12-R channel system was rationally designed and synthesized by a building block strategy, in which the interlayer expansion of a two-dimensional silicate structure was realized by combining organic amine assisted layer-stacking reorganization and subsequent silylation with a square-shaped single 4-ring (S4R) silane, 1,3,5,7-tetramethylcyclotetrasiloxane (TMCS). The PLS-3 precursor was disassembled into building blocks and then intercalated with flexible and removable organic amine pillars to offer enough interlayer spacing for accommodating TMCS molecules. The additionally introduced building blocks interconnected the neighboring layers to construct new 14-R and 12-R pores. ECNU-9 possesses a well-ordered structure with a novel topology. The corresponding Ti-ECNU-9, with tetrahedral Ti ions in the framework, showed superior catalytic performance in the selective epoxidation of bulky alkenes.

Structural diversity of lamellar zeolite Nu-6(1)--postsynthesis of delaminated analogues.

Nu-6(1) zeolite, the lamellar precursor of NSI topology, was firstly synthesized with 4'4-bipyridine as the structure-directing agent (SDA) and then subjected to HCl-EtOH treatment for the purpose of structural modification. Interlayer deconstruction and reconstruction took place alternately in this acid treatment. An intermediate named ECNU-4 was separated at the initial stage of this continuous treatment process, which exhibited a special X-ray diffraction pattern without obvious reflection peaks at low angles. The zeolitic structure in the intralayer sheets was supposed to be well preserved in ECNU-4, whereas the interlayer structure became extremely disordered. The ECNU-4 intermediate showed structural diversity. It was converted into the reconstructed and interlayer expanded zeolite IEZ-NSI without an external silicon source by prolonging the HCl-EtOH treatment to 24 h. Moreover, with a partially delaminated structure, ECNU-4 was easily interlayer swollen at room temperature with cetyltrimethyl ammonium bromide in the presence of tetrapropyl ammonium hydroxide. The swollen material was further sonicated to yield a more deeply delaminated zeolite, Del-Nu-6. ECNU-4 and Del-Nu-6 differed in delamination degree, structural disordering and textural properties, especially surface area.

Post-synthesis treatment gives highly stable siliceous zeolites through the isomorphous substitution of silicon for germanium in germanosilicates.

Germanosilicates, an important family of zeolites with increasing number of members and attractive porosities, but containing a large quantity of unstable Ge atoms in the framework, meet with great obstacles in terms of limited thermal and hydrothermal stability when it comes to practical use. A facile stabilization method thus has been developed to substitute isomorphously Ge atoms for Si atoms, giving rise to ultrastable siliceous analogues of the pristine germanosilicates.

Linear time probabilistic algorithms for the singular haplotype reconstruction problem from SNP fragments.

In this paper, we develop a probabilistic model to approach two realistic scenarios regarding the singular haplotype reconstruction problem--the incompleteness and inconsistency that occurred in the DNA sequencing process to generate the input haplotype fragments, and the common practice used to generate synthetic data in experimental algorithm studies. We design three algorithms in the model that can reconstruct the two unknown haplotypes from the given matrix of haplotype fragments with provable high probability and in linear time in the size of the input matrix. We also present experimental results that conform with the theoretical efficient performance of those algorithms. The software of our algorithms is available for public access and for real-time on-line demonstration.