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The emerging two-dimensional (2D) Dion–Jacobson (DJ) perovskites with bidentate ligands have attracted significant attention due to enhanced structural stability compared with conventional Ruddlesden–Popper (RP) perovskites with monodentate ligands linked by van der Waals interactions. However, how the pure chemical bond lattice interacts with excited state excitons and its impact on the exciton nature and dynamics in 2D DJ-perovskites, particularly in comparison to RP-perovskites, remains unexplored. Herein, by a combined spectroscopy study on excitonic and structural dynamics, we reveal a persistent exciton dressed by a weak polaronic effect in DJ-perovskite due to their rigid and harmonic lattice, in striking contrast to significantly screened exciton polaron observed in RP-perovskites. Despite the similar exciton binding energy (∼0.3 eV) in both n= 1 DJ- and RP-perovskites with near-identical crystal structure, photoexcitation results in a slightly screened exciton with minimal structural relaxation and a retained binding energy of ∼0.29 eV in DJ-perovskites but strongly screened exciton polaron with a binding energy of ∼0.13 eV in RP-perovskites. Structural dynamics further highlight the rigid and harmonic lattice motion in DJ-perovskites, as opposed to the thermally activated anharmonic lattice in RP-perovskites, arising from their distinct bonding modes. Our study offers insights into modulating excited state properties in 2D perovskites, simulating the rational design of hybrid semiconductors with tailored properties and functionalities.

Single-molecule spectroscopy offers state-resolved measurements on charge-transfer reactions of single semiconductor nanocrystals, leading to the discovery of up to six single-charge transfer reactions with seven transient states for single CdSe/CdS core/shell nanocrystals with water (or oxygen) as the hole (or electron) acceptors. Kinetic rates of three photoinduced single-hole transfer reactions decrease significantly upon increasing the number of excess electrons in a nanocrystal, mainly due to efficient Auger nonradiative recombination of the charged single excitons. Conversely, the kinetic rates of three single-electron transfer reactions of an unexcited nanocrystal increase proportionally to the number of excess electrons in it. Results here reveal that charge-transfer reactions of nanocrystals, at the center of nearly all their functions, could only be deciphered at a state-resolved level on a single nanocrystal. Size-dependent studies validate the weakly confined semiconductor nanocrystals, instead of strongly confined ones (quantum dots), as optimal candidates for photochemical and optoelectronic applications.

Zinc-blende CdSe, CdS, and CdSe/CdS core/shell nanocrystals with a structure-matched shape (cube-shaped, edge length ≤30 nm) are synthesized via a universal scheme. With the edge length up to five times larger than exciton diameter of the bulk semiconductors, the nanocrystals exhibit novel properties in the weakly confined size regime, such as near-unity single exciton and biexciton photoluminescence (PL) quantum yields, single-nanocrystal PL nonblinking, mixed PL decay dynamics of exciton and free carriers with sub-microsecond monoexponential decay lifetime, and stable yet extremely narrow PL full width at half maximum (FWHM < 0.1 meV) at 1.8 K. Their monodisperse edge length, shape, and facet structure enable demonstration of unexpected yet size-dependent PL properties at room temperature, including unusually broad and abnormally size-dependent PL FWHM (∼100 meV), nonmonotonic size dependence of PL peak energy, and dual-peak single-exciton PL. Calculations suggest that these unusual properties should be originated from the band-edge electron/hole states of the dynamic-exciton, whose exciton binding energy is too small to hold the photogenerated electron–hole pair as a bonded Wannier exciton in a weakly confined nanocrystal.

ABSTRACTIn contrast to cytoplasmic localization of spliced mRNAs, many spliced lncRNAs are localized in the nucleus. To investigate the mechanism, we used lncRNA MEG3 as a reporter and mapped a potent nuclear retention element (NRE), deletion of this element led to striking export of MEG3 from the nucleus to the cytoplasm. Insertion of the NRE resulted in nuclear retention of spliced lncRNA as well as spliced mRNA. We further purified RNP assembled on the NRE in vitro and identified the proteins by mass spectrometry. Screen using siRNA revealed depletion of U1 snRNP components SNRPA, SNRNP70 or SNRPD2 caused significant cytoplasmic localization of MEG3 reporter transcripts. Co-knockdown these factors in HFF1 cells resulted in an increased cytoplasmic distribution of endogenous lncRNAs. Together, these data support a model that U1 snRNP components restrain spliced lncRNAs in the nucleus via the interaction with nuclear retention element.

Low-dimensional lead halide perovskites with broadband emission hold great promise for single-component white-light-emitting (WLE) devices. The origin of their broadband emission has been commonly attributed to self-trapped excitons (STEs) composed of localized electronic polarization with a distorted lattice. Unfortunately, the exact electronic and structural nature of the STE species in these WLE materials remains elusive, hindering the rational design of high-efficiency WLE materials. In this study, by combining ultrafast transient absorption spectroscopy and ab initiocalculations, we uncover surprisingly similar STE features in two prototypical low dimensional WLE perovskite single crystals: 1D (DMEDA)PbBr4and 2D (EDBE)PbBr4, despite of their different dimensionalities. Photoexcited excitons rapidly localize to intrinsic STEs within ∼250 fs, contributing to the white light emission. Crucially, STEs in both systems exhibit characteristic absorption features akin to those of Pb+and Pb3+. Further atomic level theoretical simulations confirm photoexcited electrons and holes are localized on the Pb2+site to form Pb+- and Pb3+-like species, resembling transient photoinduced Pb2+disproportionation. This study provides conclusive evidence on the key excited state species for exciton self-trapping and broadband emission in low dimensional lead halide WLE perovskites and paves the way for the rational design of high-efficiency WLE materials.

Colloidal semiconductor nanocrystals are promising candidates for quantum light sources, yet their application has been impeded by photoluminescence instability due to blinking and spectral diffusion. This study introduces a new category of cube-shaped CdSe/CdS core/shell nanocrystals with exceptionally stable photoluminescence characteristics. Under continuous excitation, the emissive quantum state remained consistent without alterations of the charge state for 4000 s, and the average photon energy variation stayed within the bounds of spectral resolution throughout this extended duration. Systematic examination of single-nanocrystal photoluminescence, upon variation of the core and shell dimensions, revealed that a thicker CdS shell and increased core edge length significantly curtail spectral diffusion, considering that the nanocrystals possess well-controlled CdSe–CdS and facet–ligand interfaces. This study advances the optimization of colloidal semiconductor nanocrystals as high-performance quantum light sources.

Two-dimensional (2D) perovskites, comprising inorganic semiconductor layers separated by organic spacers, hold promise for light harvesting and optoelectronic applications. Exciton transport in these materials is pivotal for device performance, often necessitating deliberate alignment of the inorganic layers with respect to the contacting layers to facilitate exciton transport. While much attention has focused on in-plane exciton transport, little has been paid to out-of-plane interlayer transport, which presumably is sluggish and unfavorable. Herein, by time-resolved photoluminescence, we unveil surprisingly efficient out-of-plane exciton transport in 2D perovskites, with diffusion coefficients (up to ∼0.1 cm2s–1) and lengths (∼100 nm) merely a few times smaller or comparable to their in-plane counterparts. We unambiguously confirm that the out-of-plane exciton diffusion coefficient corresponds to a subpicosecond interlayer exciton transfer, governed by the Förster resonance energy transfer (FRET) mechanism. Intriguingly, in contrast to temperature-sensitive intralayer band-like transport, the interlayer exciton transport exhibits negligible temperature dependence, implying a lowest-lying bright exciton state in 2D perovskites, irrespective of spacer molecules. The robust and ultrafast interlayer exciton transport alleviates the constraints on crystal orientation that are crucial for the design of 2D perovskite-based light harvesting and optoelectronic devices.

With the identification of huge amount of noncoding RNAs in recent years, the concept of RNA localization has extended from traditional mRNA export to RNA export of mRNA and ncRNA as well as nuclear retention of ncRNA. This review aims to summarize the recent findings from studies on the mechanisms of export of different RNAs and nuclear retention of some lncRNAs in higher eukaryotes, with a focus on splicing‐dependent TREX recruitment for the export of spliced mRNA and the sequence‐dependent mechanism of mRNA export in the absence of splicing. In addition, evidence to support the involvement of m6A modification in RNA export with the coordination between the methylase complex and TREX complex as well as sequence‐dependent nuclear retention of lncRNA is recapitulated. Finally, a model of sequence‐dependent RNA localization is proposed along with the many questions that remain to be answered. This article is categorized under:RNA Export and Localization > RNA LocalizationRNA Export and Localization > Nuclear Export/Import Model of sequence‐dependent RNA localization.

An electron–hole pair in a cube-shaped CdSe/CdS core/shell nanocrystal exists in the form of dynamic excitons across the strongly and weakly confined regimes under ambient temperatures. Photochemical doping is applied to distinguish the band-edge electron and hole levels, confirming an effective mass model with universal constants. Reduction of the optical bandgap upon epitaxy of the CdS shells is caused by lowering the band-edge electron level and barely affecting the band-edge hole level. Similar shifts of the electron levels, yet retaining the hole levels, can switch the order in energy of the three lowest-energy transitions. Thermal distribution of 1–4 electrons among the two thermally accessible electron levels follows number-counting statistics, instead of Fermi–Dirac distribution.

WT1 + KTS and −KTS isoforms only differ in 3 amino acids in protein sequence but show significant functional difference. The +/−KTS isoforms were generated by alternative usage of 2 adjacent 5’ splice sites at RNA level, however, how these 2 isoforms are regulated is still elusive. Here we report the identification of an intronic pyrimidine-rich sequence that is critical for the ratio of +/−KTS isoforms, deletion or partial replacement of the sequence led to full/significant shift to -KTS isoform. To identify trans-factors that can regulate +/−KTS isoforms via the binding to the element, we performed RNP assembly using in vitro transcribed RNA with or without the pyrimidine-rich sequence. Mass spectrometry analysis of purified RNPs showed that the element associated with many splicing factors. Co-transfection of these factors with WT1 reporter revealed that HuR promoted the production of −KTS isoform at the reporter level. RNA immuno-precipitation experiment indicated that HuR interacted with the pyrimidine-rich element in WT1 intron 9. We further presented evidence that transient or stable over-expression of HuR led to enhanced expression of endogenous −KTS isoform. Moreover, knockdown of HuR resulted in decreased expression of endogenous −KTS isoform in 293T, SW620, SNU-387 and AGS cell lines. Together, these data indicate that HuR binds to the pyrimidine-rich sequence and antagonize its effect in regulating WT1 +/−KTS isoforms.

Mutations and diminished expression of the E-cadherin gene (CDH1) have been identified in a number of epithelial malignancies. Although somatic CDH1 mutations were detected in lobular breast cancer with a frequency ranging from 10–56%, CDH1 alterations in more frequent ductal tumors appear to be rare. Here we have analyzed the coding region of CDH1 for mutations using denaturing high performance liquid chromatography and found 4 mutations in 83 ductal carcinomas (5%) and 3 mutations in 25 lobular carcinomas (12%). The germline of 13 patients with familial lobular tumors was also analyzed for mutations, but none were detected. In a case-control study, we also tested whether a variant adenine allele in the promoter polymorphism −161C→A with a putative influence on the transcriptional activity of CDH1 in vitro confers any detectable risk of breast cancer. No significant difference in the allelic frequency between patients with breast cancer (326/1,152, 28.3%) and controls (190/696, 27.3%, p > 0.05; relative risk 1.05, 95% confidence interval 0.85–1.30) was found. A novel promoter polymorphism was identified at position −152, but the frequency of the variant cytosine allele was also similar in patients with breast cancer and controls (0.71% vs. 0.21%, p = 0.23). Transient transfection experiments using reporter constructs containing the nucleotide substitutions −161C/−152C and −161A/−152T showed only a slight decrease in the transcription activity compared to the wild-type construct. These results do not support CDH1 as a prominent low-penetrance cancer susceptibility gene, but indicate that CDH1 mutations contribute to the progression of both lobular and ductal tumors. © 2001 Wiley-Liss, Inc.

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