Conversion between Triplet Pair States Is Controlled by Molecular Coupling in Pentadithiophene Thin Films

In singlet fission (SF) the initially formed correlated triplet pair state, 1(TT), may evolve toward independent triplet excitons or higher spin states of the (TT) species. The latter result is often considered undesirable from a light harvesting perspective but may be attractive for quantum information sciences (QIS) applications, as the final exciton pair can be spin-entangled and magnetically active with relatively long room temperature decoherence times. In this study we use ultrafast transient absorption (TA) and time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy to monitor SF and triplet pair evolution in a series of alkyl silyl-functionalized pentadithiophene (PDT) thin films designed with systematically varying pairwise and long-range molecular interactions between PDT chromophores. The lifetime of the (TT) species varies from 40 ns to 1.5 μs, the latter of which is associated with extremely weak intermolecular coupling, sharp optical spectroscopic features, and complex TR-EPR spectra that are composed of a mixture of triplet and quintet-like features. On the other hand, more tightly coupled films produce broader transient optical spectra but simpler TR-EPR spectra consistent with significant population in 5(TT)0. These distinctions are rationalized through the role of exciton diffusion and predictions of TT state mixing with low exchange coupling J versus pure spin substate population with larger J. The connection between population evolution using electronic and spin spectroscopies enables assignments that provide a more detailed picture of triplet pair evolution than previously presented and provides critical guidance for designing molecular QIS systems based on light-induced spin coherence

Practical Guidance for Integrating Data Management into Long-Term Ecological Monitoring Projects

Long-term monitoring and research projects are essential to understand ecological change and the effectiveness of management activities. An inherent characteristic of long-term projects is the need for consistent data collection over time, requiring rigorous attention to data management and quality assurance. Recent papers have provided broad recommendations for data management; however, practitioners need more detailed guidance and examples. We present general yet detailed guidance for the development of comprehensive, concise, and effective data management for monitoring projects. The guidance is presented as a graded approach, matching the scale of data management to the needs of the organization and the complexity of the project. We address the following topics: roles and responsibilities; consistent and precise data collection; calibration of field crews and instrumentation; management of tabular, photographic, video, and sound data; data completeness and quality; development of metadata; archiving data; and evaluation of existing data from other sources. This guidance will help practitioners execute effective data management, thereby, improving the quality and usability of data for meeting project objectives as well as broader meta-analysis and macrosystem ecology research

Detecting and Visualizing Reaction Intermediates of Anisotropic Nanoparticle Growth

This paper describes a correlative approach to detect, visualize, and characterize intermediate species during a seedless, anisotropic nanoparticle synthesis. Changes in radical concentration as a function of time were correlated in situ to the optical properties and morphology of the particles. Depending on type and concentration of reaction precursors, either one or two increases in radical production occurred, corresponding to initial particle formation and increased branch length, respectively. Thus, changes in radical intensity can be considered as an indicator of nanoparticle structure and properties

Spin-Selective Photoreduction of a Stable Radical within a Covalent Donor–Acceptor–Radical Triad

Controlling spin–spin interactions in multispin molecular assemblies is important for developing new approaches to quantum information processing. In this work, a covalent electron donor–acceptor–radical triad is used to probe spin-selective reduction of the stable radical to its diamagnetic anion. The molecule consists of a perylene electron donor chromophore (D) bound to a pyromellitimide acceptor (A), which is, in turn, linked to a stable α,γ-bisdiphenylene-β-phenylallyl radical (R^•) to produce D-A-R^•. Selective photoexcitation of D within D-A-R^• results in ultrafast electron transfer to form the D^+•-A^–•-R^• triradical, where D^+•-A^–• is a singlet spin-correlated radical pair (SCRP), in which both SCRP spins are uncorrelated relative to the R^• spin. Subsequent ultrafast electron transfer within the triradical forms D^+•-A-R^–, but its yield is controlled by spin statistics of the uncorrelated A^–•-R^• radical pair, where the initial charge separation yields a 3:1 statistical mixture of D^+•-³(A^–•-R^•) and D^+•-¹(A^–•-R^•), and subsequent reduction of R^• only occurs in D^+•-¹(A^–•-R^•). These findings inform the design of multispin systems to transfer spin coherence between molecules targeting quantum information processing using the agency of SCRPs

TGFβ signalling is required to maintain pluripotency of human naïve pluripotent stem cells.

Funder: Cambridge Hospitals National Institute for Health Research Biomedical Research CenterFunder: Gates Cambridge TrustFunder: Department of HealthThe signalling pathways that maintain primed human pluripotent stem cells (hPSCs) have been well characterised, revealing a critical role for TGFβ/Activin/Nodal signalling. In contrast, the signalling requirements of naive human pluripotency have not been fully established. Here, we demonstrate that TGFβ signalling is required to maintain naive hPSCs. The downstream effector proteins - SMAD2/3 - bind common sites in naive and primed hPSCs, including shared pluripotency genes. In naive hPSCs, SMAD2/3 additionally bind to active regulatory regions near to naive pluripotency genes. Inhibiting TGFβ signalling in naive hPSCs causes the downregulation of SMAD2/3-target genes and pluripotency exit. Single-cell analyses reveal that naive and primed hPSCs follow different transcriptional trajectories after inhibition of TGFβ signalling. Primed hPSCs differentiate into neuroectoderm cells, whereas naive hPSCs transition into trophectoderm. These results establish that there is a continuum for TGFβ pathway function in human pluripotency spanning a developmental window from naive to primed states