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The dynamics of strongly coupled polariton systems integrated with 2D transition metal dichalcogenides (TMDs) is key to enabling efficient coherent processes and achieving high-performance TMD-based polaritonic devices, such as ultralow-threshold polariton lasers and ultrafast optical switches. However, there has been a lack of a comprehensive understanding of the excited state dynamics in TMD-based polariton systems. In this work, ultrafast pump-probe optical spectroscopy is used to investigate the room temperature dynamics of the polariton systems consisting of TMD monolayer excitons strongly coupled with Bloch surface waves (BSWs) supported by all-dielectric photonic structures. The transient response is found for both above-exciton energy pumping and polariton-resonant pumping. The excited state population and ultrafast coherent coupling of the exciton reservoir and lower polariton (LP) branch are observed for resonant pumping. Moreover, it is found that the transient response of the LP first decays on a short-time scale of 0.15-0.25 ps compared to the calculated intrinsic lifetime of 0.11-0.20 ps, and is followed by a longer decay (>100 ps) due to the dynamical evolution of the exciton reservoir. The results provide a fundamental understanding of the dynamics of TMD-based polariton systems while showing the potential for achieving efficient coherent optical processes for device applications., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Schiff bases are a crucial component in various functional materials but often exhibit non-emissive behavior which significantly limits their potential applications as luminescent materials. However, traditional approaches to convert them into aggregate emitters often require intricate molecular design, tedious synthesis, and significant time and resource consumption. Herein, we present a cocrystallization-induced emission strategy that can transform non-emissive (hetero)aryl-substituted Schiff bases into green-yellow to yellow aggregate emitters via even simple grinding of a mixture of Schiff bases and 1,2,4,5-tetracyanobenzene (TCB) mixtures. The combined experimental and theoretical analysis revealed that the cocrystallization inhibits the C=N isomerization and promotes face-to-face π-π interaction, which restricts access to both the dark state and canonical intersection to ultimately induce emission. Furthermore, the induced emission enables the observation of solid-state molecular diffusion through fluorescence signals, advancing white light emission diodes, and notably, solution-processed organic light-emitting diodes based on cocrystal for the first time. This study not only highlights the potential of developing new C=N structural motifs for AIEgens but also could boost advancements in related structure motifs like C=C and N=N., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Singlet fission is commonly defined as the generation of two triplet excitons from a single absorbed photon. However, ambiguities within this definition arise due to the complexity of the various double triplet states that exist in SF chromophores and the corresponding interconversion processes. To clarify this process, singlet fission is frequently depicted as sequential two-step conversion in which a singlet exciton decays into a bound triplet-pair biexciton state that dissociates into two "free" triplet excitons. However, this model discounts the potential for direct harvesting from the coupled biexciton state. Here, it is demonstrated that individual triplet excitons can be extracted directly from a bound triplet pair. It is demonstrated that due to the requirement for geminate triplet-triplet annihilation in intramolecular singlet fission compounds, unique spectral and kinetic signatures can be used to quantify triplet-pair harvesting yields. An internal quantum efficiency for triplet exciton transfer from the triplet pair of >50%, limited only by the solubility of the compounds is achieved. The harvesting process is not dependent on the net multiplicity of the triplet-pair state, suggesting that an explicit, independent dissociation step is not a requirement for using triplet pairs to do chemical or electrical work., (© 2022 Wiley-VCH GmbH.)

The synthesis and structure of atomically precise Au 130-x Ag x (average x=98) alloy nanoclusters protected by 55 ligands of 4-tert-butylbenzenethiolate are reported. This large alloy structure has a decahedral M 54 (M=Au/Ag) core. The Au atoms are localized in the truncated Marks decahedron. In the core, a drum of Ag-rich sites is found, which is enclosed by a Marks decahedral cage of Au-rich sites. The surface is exclusively Ag-SR; X-ray absorption fine structure analysis supports the absence of Au-S bonds. The optical absorption spectrum shows a strong peak at 523 nm, seemingly a plasmon peak, but fs spectroscopic analysis indicates its non-plasmon nature. The non-metallicity of the Au 130-x Ag x nanocluster has set up a benchmark to study the transition to metallic state in the size evolution of bimetallic nanoclusters. The localized Au/Ag binary architecture in such a large alloy nanocluster provides atomic-level insights into the Au-Ag bonds in bimetallic nanoclusters., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A comprehensive investigation into the spectral properties and excitation energy transfer in di- or tribranched dithienyldiketopyrrolopyrrole (DPP) molecules with meta-substituted benzene as a central core (TADPP2-TT and TADPP3), by means of steady-state and transient measurements and quantum chemical calculations, is reported. Excitation in the meta-substituted chromophores is localized on one of the DPP units in the branching molecules owing to the disruption of conjugation by meta substitution for both TADPP2-TT and TADPP3. Weak electronic couplings result from the long distance between the DPP chromophores and the steric effects from the attached side chains on DPP. The attachment of the acetylene linker in each branch, which has a very low twisting barrier, could also play an important role in reducing the interaction between DPP chromophores. The dynamics of the excited states show that excitation energy transfer occurs on the picosecond scale, which is attributed to the incoherent hopping mechanism., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)