Dynamics of Solvent-Mediated Electron Localization in Electronically Excited Hexacyanoferrate(III)

We have used polarization-resolved UV pump–mid-IR probe spectroscopy to investigate the dynamics of electron hole localization for excited-state ligand-to-metal charge-transfer (LMCT) excitation in Fe­(CN)₆^3–. The initially generated LMCT excited state has a single CN-stretch absorption band with no anisotropy. This provides strong evidence that this initial excited state preserves the octahedral symmetry of the electronic ground state by delocalizing the ligand hole in the LMCT excited state on all six cyanide ligands. This delocalized LMCT excited state decays to a second excited state with two CN-stretch absorption bands. We attribute both peaks to a single excited state because the formation time for both peaks matches the decay time for the delocalized LMCT excited state. The presence of two CN-stretch absorption bands demonstrates that this secondary excited state has lower symmetry. This observation, in conjunction with the solvent-dependent time constant for the formation of the secondary excited state, leads us to conclude that the secondary excited state corresponds to a LMCT state with a localized ligand hole

Resolving Photo-Induced Twisted Intramolecular Charge Transfer with Vibrational Anisotropy and TDDFT

The interplay between reaction environment and photochemical outcome has wide ranging implications for designing and directing light driven chemical conversions. We present a detailed mechanistic description of photoisomerization in julolidine malononitrile (JDMN) as the first step to characterizing this interplay between reaction pathways and reaction environment. We have used polarization resolved UV pump–mid-IR probe spectroscopy and time dependent DFT calculations to investigate the dynamics of charge transfer induced intramolecular rotation in JDMN. We have probed the mechanism and dynamics of photoisomerization with the symmetric and antisymmetric CN-stretch of the malononitrile group. These measurements show the S1 electronic excited state relaxes with a 12.3 ps time constant by isomerizing around both the C–C single and C–C double bond of the malononitrile group with a branching ratio of 1:5. Isomerization around the single bond leads to the formation of a metastable twisted excited state, while isomerization around the double bond leads to excited state quenching via a conical intersection between the S1 and S0 electronic states. We have characterized the electronic and nuclear structure of the long-lived excited state with pump–probe anisotropy measurements and time dependent DFT calculations using the CAM-B3LYP functional and the 6-31G­(d,p) basis set. These calculations further confirm that isomerization around the malononitrile single bond forms a twisted intermolecular charge transfer excited state

Photonic Emulator for Inverse Design

Inverse design has become a powerful tool widely used in the design of high-performance integrated photonic devices. However, current inverse design methods rely heavily on computationally intensive electromagnetic simulation or time-consuming model training. Here, we proposed an efficient inverse design strategy, called a photonic emulator, that uses light propagation instead of electromagnetic simulation. We experimentally demonstrated the application of this photonic emulator for various typical single- and multiwavelength devices and functions, such as an optical multiple-input–multiple-output (MIMO) descrambler (at the modulation rate of 10 Gbit/s), matrix computation (percentage error < 2%), and a tunable wavelength selective switch (extinction ratio > 10 dB for three-wavelength routing). The photonic emulator enables high-precision reconfiguration of the design target on the basis of precise tuning of the effective refractive index near the pixels in the design area and fast feedback of the optical response in real time. Our work shows that the concept of propagation-as-computation can be used for inverse design to provide an efficient method for designing reconfigurable integrated photonic devices

Aqueous Mg²⁺ and Ca²⁺ Ligand Exchange Mechanisms Identified with 2DIR Spectroscopy

Biological systems must discriminate between calcium and magnesium for these ions to perform their distinct biological functions, but the mechanism for distinguishing aqueous ions has yet to be determined. Ionic recognition depends upon the rate and mechanism by which ligands enter and leave the first solvation shell surrounding these cations. We present a time-resolved vibrational spectroscopy study of these ligand exchange dynamics in aqueous solution. The sensitivity of the CN-stretch frequency of NCS^– to ion pair formation has been utilized to investigate the mechanism and dynamics of ligand exchange into and out of the first solvation shell of aqueous magnesium and calcium ions with multidimensional vibrational (2DIR) spectroscopy. We have determined that anion exchange follows a dissociative mechanism for Mg²⁺ and an associative mechanism for Ca²⁺

Intrachain and Interchain Excited-State Dynamics of Temperature-Dependent Aggregation Copolymer in Solution

Poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis (2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione)] (PBDB-T) is a donor–acceptor copolymer widely used as a donor material in high-efficiency organic solar cells. In this work, we studied the temperature-dependent aggregation properties of PBDB-T in solution. Through the characterization of UV–vis absorption and the photoluminescence spectrum, we found that PBDB-T formed strong interchain interactions that facilitate aggregation at room temperature. In contrast, warmer temperatures cause PBDB-T to coil and increase intrachain interactions, thus reducing aggregation. We further use transient absorption spectroscopy to explore the effect of temperature-dependent aggregation behavior on excited-state dynamics. The results show that the intrachain interaction is beneficial to increase the production of polaron pairs, and the interchain interaction is beneficial to accelerate the production of free polarons. Finally, we investigated the corresponding films and demonstrated that regulating the solution aggregation is an effective way to control the crystallinity, and morphology of the corresponding films

Engineering the Co(II)/Co(III) Redox Cycle and Co^δ+ Species Shuttle for Nitrate-to-Ammonia Conversion

Electroreduction of waste nitrate to valuable ammonia offers a green solution for environmental restoration and energy storage. However, the electrochemical self-reconstruction of catalysts remains a huge challenge in terms of maintaining their stability, achieving the desired active sites, and managing metal leaching. Herein, we present an electrical pulse-driven Co surface reconstruction-coupled Coδ+ shuttle strategy for the precise in situ regulation of the Co(II)/Co(III) redox cycle on the Co-based working electrode and guiding the dissolution and redeposition of Co-based particles on the counter electrode. As result, the ammonia synthesis performance and stability are significantly promoted while cathodic hydrogen evolution and anodic ammonia oxidation in a membrane-free configuration are effectively blocked. A high rate of ammonia production of 1.4 ± 0.03 mmol cm–2 h–1 is achieved at −0.8 V in a pulsed system, and the corresponding nitrate-to-ammonia Faraday efficiency is 91.7 ± 1.0%. This work holds promise for the regulation of catalyst reactivity and selectivity by engineering in situ controllable structural and chemical transformations

Identification and Characterization of MicroRNAs by High Through-Put Sequencing in Mesenchymal Stem Cells and Bone Tissue from Mice of Age-Related Osteoporosis

<div><p>The functional deficiencies of bone marrow-derived mesenchymal stem cells (MSCs) may contribute to the aging process and age-related diseases, such as osteoporosis. Although it has been reported that microRNAs (miRNAs) played an important role in mechanisms of gene regulation of aging, and their expression profiles in MSCs osteogenic differentiation were established in recent years, but it is still elusive for the dynamic patterns of miRNAs in aging process. Importantly, the miRNAs in aged bone tissue had not been yet reported so far. Here, we combined high through-put sequencing with computational techniques to detect miRNAs dynamics in MSCs and bone tissue of age-related osteoporosis. Among the detected miRNAs, 59 identified miRNAs in MSCs and 159 in bone showed significantly differential expressions. And more importantly, there existed 8 up-regulated and 30 down-regulated miRNAs in both MSCs and bone during the aging process, with the majority having a trend of down-regulation. Furthermore, after target prediction and KEGG pathway analysis, we found that their targeted genes were significantly enriched in pathways in cancer, which are complex genetic networks, comprise of a number of age-related pathways. These results strongly suggest that these analyzed miRNAs may be negatively involved in age-related osteoporosis, given that most of them showed a decreased expression, which could lay a good foundation for further functional analysis of these miRNAs in age-related osteoporosis.</p></div

Effect of Fluorinated End-Groups on the Exciton Dynamics and Charge Transfer of Non-fused Ring Acceptors

In recent years, the optimization of non-fused ring electron acceptors (NFREAs) has become an important topic, which includes π extension, side-chain engineering, and end-group halogenation. While the performance characterization of different NFREAs, including their morphology and power conversion efficiencies, has been extensively studied, the influence of different optimization methods on their photophysical processes is not clear. Here, we analyze the effect of end-group fluoridation on exciton dynamics and charge transfer (CT) in NFREA-based organic photovoltaics in detail using a novel NFREA Isopropyl-0F and its end-group fluorinated homologue Isopropyl-2F by means of spectroscopy, in order to understand the physical mechanism for the differences in their performance. The transient absorption spectra show that the more ordered molecular arrangement in the Isopropyl-2F-based heterojunction resulted in faster exciton diffusion and higher hole transfer efficiency, which were conducive to CT and reduced recombination loss. These results well explain the improved properties after end-group fluoridation

miRNA expression validated by qRT-PCR in MSCs and bone.

<p>qPCR results were normalized to U6 snRNA expression levels. Values showed that these miRNAs were significantly different between 2m and 25m samples.</p

Summary of changed miRNAs during bone aging.

<p>Summary of changed miRNAs during bone aging.</p