Reversible Expansion Research Articles

Thin-film chemical expansion of ceria based solid solutions: laser vibrometry study

Abstract The chemical expansion of Pr0.1Ce0.9O2–δ (PCO) and CeO2–δ thin films is investigated in the temperature range between 600 °C and 800 °C by laser Doppler vibrometry (LDV). It enables non-contact determination of nanometer scale changes in film thickness at high temperatures. The present study is the first systematic and detailed investigation of chemical expansion of doped and undoped ceria thin films at temperatures above 650 °C. The thin films were deposited on yttria stabilized zirconia substrates (YSZ), operated as an electrochemical oxygen pump, to periodically adjust the oxygen activity in the films, leading to reversible expansion and contraction of the film. This further leads to stresses in the underlying YSZ substrates, accompanied by bending of the overall devices. Film thickness changes and sample bending are found to reach up to 10 and several hundred nanometers, respectively, at excitation frequencies from 0.1 to 10 Hz and applied voltages from 0–0.75 V for PCO and 0–1 V for ceria. At low frequencies, equilibrium conditions are approached. As a consequence maximum thin-film expansion of PCO is expected due to full reduction of the Pr ions. The lower detection limit for displacements is found to be in the subnanometer range. At 800 °C and an excitation frequency of 1 Hz, the LDV shows a remarkable resolution of 0.3 nm which allows, for example, the characterization of materials with small levels of expansion, such as undoped ceria at high oxygen partial pressure. As the correlation between film expansion and sample bending is obtained through this study, a dimensional change of a free body consisting of the same material can be calculated using the high resolution characteristics of this system. A minimum detectable dimensional change of 5 pm is estimated even under challenging high-temperature conditions at 800 °C opening up opportunities to investigate electro-chemo-mechanical phenomena heretofore impossible to investigate. The expansion data are correlated with previous results on the oxygen nonstoichiometry of PCO thin films, and a defect model for bulk ceria solid solutions is adopted to calculate the cation and anion radii changes in the constrained films during chemical expansion. The constrained films exhibit anisotropic volume expansion with displacements perpendicular to the substrate plane nearly double that of bulk samples. The PCO films used here generate high total displacements of several 100 nm’s with high reproducibility. Consequently, PCO films are identified to be a potential core component of high-temperature actuators. They benefit not only from high displacements at temperatures where most piezoelectric materials no longer operate while exhibiting, low voltage operation and low energy consumption.

The role of thermodynamically stable configuration in enhancing crystallographic diffraction quality of flexible MOFs

SummarySingle-crystal X-ray diffraction (SCXRD) is a widely used method for structural characterization. Generally, low temperature is of great significance for improving the crystallographic diffraction quality. Herein we observe that this practice is not always effective for flexible metal-organic frameworks (f-MOFs). An abnormal crystallography, that is, more diffraction spots at a high angle and better resolution of diffraction data as the temperature increases in the f-MOF (1-g), is observed. XRD results reveal that 1-g has a reversible anisotropic thermal expansion behavior with a record-high c-axial positive expansion coefficient of 1,401.8 × 10−6 K−1. Calculation results indicate that the framework of 1-g has a more stable thermodynamic configuration as the temperature increases. Such configuration has lower-frequency vibration and may play a key role in promoting higher Bragg diffraction quality at room temperature. This work is of great significance for how to obtain high-quality SCXRD diffraction data.

Bidirectional and reversible tuning of the interlayer spacing of two-dimensional materials

Interlayer spacing is expected to influence the properties of multilayer two-dimensional (2D) materials. However, the ability to non-destructively regulate the interlayer spacing bidirectionally and reversibly is challenging. Here we report the preparation of 2D materials with tunable interlayer spacing by introducing active sites (Ce ions) in 2D materials to capture and immobilize Pt single atoms. The strong chemical interaction between active sites and Pt atoms contributes to the intercalation behavior of Pt atoms in the interlayer of 2D materials and further promotes the formation of chemical bonding between Pt atom and host materials. Taking cerium-embedded molybdenum disulfide (MoS2) as an example, intercalation of Pt atoms enables interlayer distance tuning via an electrochemical protocol, leading to interlayer spacing reversible and linear compression and expansion from 6.546 ± 0.039 Å to 5.792 ± 0.038 Å (~11 %). The electronic property evolution with the interlayer spacing variation is demonstrated by the photoluminescence (PL) spectra, delivering that the well-defined barrier between the multilayer and monolayer layered materials can be artificially designed.

Reversible and Irreversible Expansion of Lithium-Ion Batteries Under a Wide Range of Stress Factors

Lithium-ion batteries cell thickness changes as they degrade. These changes in thickness consist of a reversible intercalation-induced expansion and an irreversible expansion. In this work, we study the cell expansion evolution under variety of conditions such as temperature, charging rate, depth of discharge, and pressure. A specialized fixture was used to keep the cells at a constant pressure during cycling, while measuring the thickness change both within a cycle and the cumulative growth over many cycles. The changes in positive and negative electrode capacity and stoichiometric range can be diagnosed from the evolution of the reversible expansion. The changes in the reversible expansion if combined with the voltage, lead to a higher-confidence estimation of cell health parameters important for lifetime prediction and adaptive battery management such as asymmetric charge/discharge power limits. This study raises the importance of monitoring the expansion for enabling advanced and more-informed health diagnostics of lithium-ion batteries.

Dihydroartemisinin Beneficially Regulates Splenic Immune Cell Heterogeneity Through the SOD3-JNK-AP-1 Axis

Background: The immunomodulatory potential of dihydroartemisinin (DHA) has recently been highlighted; however, the potential mechanism remains to be clarified. Methods: To elucidate the immunomodulatory mechanisms of DHA, single-cell RNA sequencing was explored in combination with cellular and biochemical approaches. Findings: In this study, we found that DHA induced both spleen enlargement and rearrangement of splenic immune cell subsets in mice. It was revealed that DHA promoted the reversible expansion of effective regulatory T cells and interferon-γ + cytotoxic CD8 + T cells in the spleen via induction of superoxide dismutase 3 (SOD3) expression and increased phosphorylation of c-Jun N-terminal kinases (JNK) and its downstream activator protein 1 (AP-1) transcription factors. Further, SOD3 knockout mice were resistant to the regulatory effect of DHA. Interpretation: Thus, DHA, through the activation of the SOD3-JNK-AP-1 axis, beneficially regulated immune cell heterogeneity and splenic immune cell homeostasis to treat autoimmune diseases. Funding: This research was supported by National Nature and Science Foundation of China (82030060) and CAMS Innovation Fund for Medical Sciences (CIFMS) (2019-I2M-5-042). Y.Z., Q.L., and N.J. contributed equally to this study. Declaration of Interest: None to declare. Ethical Approval: All experimental procedures were conducted in accordance with the animal husbandry guidelines of Shenyang Agricultural University. The Ethical Committee of Shenyang Agricultural University approved the laboratory animal experiments (Permit No. SYXK

Giant negative thermal expansion in a textured MnCoSi alloy

In the present work, textured stoichiometric MnCoSi alloys were fabricated by slow-cooling thermal treatment. Microstructure and crystallographic characterization revealed that the textured MnCoSi alloy consists of three different oriented orthorhombic TiNiSi-type martensite variants with their aOrth-axis lying in the cross-section of the rod-like MnCoSi alloy. A giant reversible linear negative thermal expansion (NTE) as much as 9350 ppm was achieved along the aOrth-axis of the textured MnCoSi alloy at a wide operation temperature span from 50 K to 400 K, owing to the antiferromagnetic arrangement. The linear NTE value slightly decreases from 9350 ppm to 9200 ppm with increasing the external magnetic field up to 2 T, which indicates that the present MnCoSi alloy demonstrates a stable NTE effect under external magnetic field. Moreover, during the martensitic transformation, the linear NTE along the aOrth-axis of the textured MnCoSi alloy could be up to 70,000 ppm at about 1200 K.

Анализ процесса обратного расширения в поршневой гибридной энергетической машине с двумя всасывающими клапанами

The paper analyzes the existing design schemes of hybrid power machines with a coolant moving in the jacket space due to the vacuum at the suction and introduces a new design of a single-stage single-cylinder piston hybrid power machine with two suction valves, in which the forced movement of the coolant in the forward direction is provided due to the vacuum at the suction, and in the reverse direction due to the pressure drop of the compressed gas. The analysis of the reverse expansion process allowed us to determine the value of the reduced dead space, which directly affects the volumetric feed rate of the reciprocating compressor and the feed rate in general. The parametric analysis made it possible to determine the influence of the main design and operating parameters on the value of the reduced dead space and accordingly on the volumetric feed rate. The results obtained can be useful in the design and research of reciprocating hybrid power machines with the forced movement of the coolant.

Management of Tessier Type 3 Cleft With a Novel Reverse Palatal Expander.

The purpose of this clinical report is to present the novel management of a type Tessier 3 cleft which was treated using a palatal expander in reverse fashion to reapproximate the craniofacial skeleton allowing for closure of the palate and soft tissue of the cleft. Reapproximation of the bony component of the cleft was achieved without osteotomies and allowed for easier and earlier realignment of the bony and soft tissue components of the cleft. To our knowledge, this is the first use of reverse palatal expansion in the treatment of type 3 Tessier cleft. Reverse palatal expansion made management of this cleft more straightforward and should be considered as a useful adjunct in the management of wide facial clefts.

Progesterone receptor antagonists reverse stem cell expansion and the paracrine effectors of progesterone action in the mouse mammary gland

BackgroundThe ovarian hormones estrogen and progesterone (EP) are implicated in breast cancer causation. A specific consequence of progesterone exposure is the expansion of the mammary stem cell (MSC) and luminal progenitor (LP) compartments. We hypothesized that this effect, and its molecular facilitators, could be abrogated by progesterone receptor (PR) antagonists administered in a mouse model.MethodsOvariectomized FVB mice were randomized to 14 days of treatment: sham, EP, EP + telapristone (EP + TPA), EP + mifepristone (EP + MFP). Mice were then sacrificed, mammary glands harvested, and mammary epithelial cell lineages separated by flow cytometry using cell surface markers. RNA from each lineage was sequenced and differential gene expression was analyzed using DESeq. Quantitative PCR was performed to confirm the candidate genes discovered in RNA seq. ANOVA with Tukey post hoc analysis was performed to compare relative expression. Alternative splicing events were examined using the rMATs multivariate analysis tool.ResultsSignificant increases in the MSC and luminal mature (LM) cell fractions were observed following EP treatment compared to control (p < 0.01 and p < 0.05, respectively), whereas the LP fraction was significantly reduced (p < 0.05). These hormone-induced effects were reversed upon exposure to TPA and MFP (p < 0.01 for both). Gene Ontology analysis of RNA-sequencing data showed EP-induced enrichment of several pathways, with the largest effect on Wnt signaling in MSC, significantly repressed by PR inhibitors. In LP cells, significant induction of Wnt4 and Rankl, and Wnt pathway intermediates Lrp2 and Axin2 (confirmed by qRTPCR) were reversed by TPA and MFP (p < 0.0001). Downstream signaling intermediates of these pathways (Lrp5, Mmp7) showed similar effects. Expression of markers of epithelial-mesenchymal transition (Cdh1, Cdh3) and the induction of EMT regulators (Zeb1, Zeb2, Gli3, Snai1, and Ptch2) were significantly responsive to progesterone. EP treatment was associated with large-scale alternative splicing events, with an enrichment of motifs associated with Srsf, Esrp, and Rbfox families. Exon skipping was observed in Cdh1, Enah, and Brd4.ConclusionsPR inhibition reverses known tumorigenic pathways in the mammary gland and suppresses a previously unknown effect of progesterone on RNA splicing events. In total, our results strengthen the case for reconsideration of PR inhibitors for breast cancer prevention.

Numerical Simulation of Damage Behaviour of Building Sandstone Exposed to Fire

In this study, numerical simulations of the behaviour of large-size sandstone specimens exposed to wood crib fires were conducted. The developed numerical model, which innovatively considers the reversible quartz expansion behaviour during heating–cooling cycles, can replicate the temperature distributions, cracking behaviours, and strength variations of sandstone samples under various thermal loads (e.g., fires). Results show that the cracking mechanisms during heating and cooling are different, and the spalling is due to their combining effects. During the heating process, tensile stresses are induced mainly inside the sample due to significant expansions of the outer layer. The induced tensile microcracks beneath the surface will be furtherly extended and widened due to the re-distributed local stresses caused by local failures. After the fire, significant tensile stresses appear in the outer part of the sample due to the increased thermal gradients (i.e., volumetric expansions) of the inner part, leading to crack widening on the surface. These widened cracks will coalesce with the heating-induced cracks in the earlier time and boost the fracturing and spalling behaviour until the temperature across the sample reaches an equilibrium state. The findings are essential for understanding the failure mechanism of sandstone during real fire development. The good agreements between lab tests and numerical simulation also reveal the feasibility of using numerical models to predict the fire-induced damage in sandstone elements in architecture.

Reversible difference expansion multi-layer data hiding technique for medical images

Maintaining the privacy and security of confidential information in data communication has always been a major concern. It is because the advancement of information technology is likely to be followed by an increase in cybercrime, such as illegal access to sensitive data. Several techniques were proposed to overcome that issue, for example, by hiding data in digital images. Reversible data hiding is an excellent approach for concealing private data due to its ability to be applied in various fields. However, it yields a limited payload and the quality of the image holding data (Stego image), and consequently, these two factors may not be addressed simultaneously. This paper addresses this problem by introducing a new non-complexity difference expansion (DE) and block-based reversible multi-layer data hiding technique constructed by exploring DE. Sensitive data are embedded into the difference values calculated between the original pixels in each block with relatively low complexity. To improve the payload capacity, confidential data are embedded in multiple layers of grayscale medical images while preserving their quality. The experiment results prove that the proposed technique has increased the payload with an average of 369999 bits and kept the peak signal to noise ratio (PSNR) to the average of 36.506 dB using medical images' adequate security the embedded private data. This proposed method has improved the performance, especially the secret size, without reducing much the quality. Therefore, it is suitable to use for relatively big payloads.

In situ heating studies on temperature-induced phase transitions in epitaxial Hf0.5Zr0.5O2/La0.67Sr0.33MnO3 heterostructures

Hafnia-based thin films exhibit unconventional ferroelectricity. These materials also show rich polymorphism, and thus temperature and field-driven phase transitions, as well as oxygen migration. In a bigger context of exploring the synergy between ferroelectricity and diffusion-based structural phenomena, here we study temperature-dependent phase transitions in epitaxial Hf0.5Zr0.5O2(HZO)/La0.67Sr0.33MnO3 (LSMO, bottom electrode) heterostructures. We report topotactic phase transitions and their clear pathways in both LSMO and HZO layers upon heating under vacuum, using in situ scanning transmission electron microscopy (STEM). Specifically, we directly image oxygen and cationic columns using integrated differential phase contrast STEM and follow their evolution with temperature. We also perform in situ high temperature x-ray diffraction in air and show that the LSMO layer undergoes reversible thermal expansion and contraction when heated up to 850 °C, whereas HZO undergoes strain relaxation beyond 750 °C without any reversible phase transition. Our results provide a comprehensive and direct understanding of temperature-dependent structure, defect, and property correlations in these systems.

THE EFFECTIVENESS OF ACTIVE MODIFIED PRESURGICAL NASOALVEOLAR APPLIANCE IN ALIGNMENT OF PREMAXILLA OF COMPLETE BILATERAL CLEFT LIP AND PALATE INFANTS

INTRODUCTION: Complete bilateral cleft lip and palate CBCLP is considered the most difficult form of cleft cases nowadays. Nasoalveolar molding enhances the esthetic and functional results of cleft infants. NAM works on the principle of sculpting and molding of the alveolus and adjacent soft tissues.OBJECTIVES: The aim of this study was to assess the efficiency of a presurgical modified screw activated NAM appliance in retruding the premaxilla for CBCLP infants.MATERIALS AND METHODS: Fifteen CBCLP infant were included in the study. Preliminary maxillary impressions were made and the produced casts were scanned to obtain three-dimensional virtual image which was used to plan the design of the appliance. Two-piece acrylic active appliance with reverse expansion screw was used to retrude the premaxilla. The appliance was retained in place using niklel chromium side extension arms and head cap. When the cleft gap was closed to be suitable for surgical repair, primary lip repair was performed. Impressions were made again; the casts were scanned to be converted into 3D models on which linear analysis of the cleft gap was done.RESULTS: The results showed statistically significant decrease in the cleft gap following active alveolar molding.CONCLUSION: Active NAM appliance can effectively retrude and correct the severely rotated and deviated premaxilla providing better esthetic results.

Solvent-mediated framework flexibility of interdigitated 2D layered metal–organic frameworks

The 2D framework with guest molecules in the solvent pores shows reversible framework expansion and contraction, whereas the 2D framework without guest molecules does not show framework expansion under the same conditions.

Моделювання й оптимізація собівартості продукції підприємницької структури

The article is aimed at analyzing the production self-cost of dairy products as an indicator of the efficiency of the economic activity of the entrepreneurial structure. The analysis consists in: determining which indicators of the articles of calculation form the self-cost of production for a certain period of their description; modeling the degree of influence of the calculation elements on the indicator; search and selection of practical measures to optimize the production self-cost of products of the enterprise Kharkiv Dairy Plant LLC. In the course of analysis of the dairy market of Ukraine, important problems of the industry are highlighted and the following factors of influence on the self-cost of production are identified: shortage of dairy raw materials, increasing the share of imported goods, and industrialization of enterprises. The dynamics of changes in the structure of production self-cost and production volume of dairy enterprise products within 22 months is considered. It was found that the main impact on the production self-cost have raw materials and wages of employees. After solving the equation of multiple linear regression using matrices, an adequate economic and mathematical model is obtained with the level of influence of six articles of calculation on the production self-cost of 1 tons of the fermented milk drink with the «Laktomix» fruit filler. The articles of calculation, in turn, represent the sum of productions of specific norms of costs and prices for them. Practical measures to optimize and reduce the production self-cost of dairy products on the part of the enterprise and on the part of the State are considered. Some measures are already being implemented at the enterprise, the other still exist only in the plans. One of the effective measures to optimize the self-cost of production is the use of membrane technologies, innovative biotechnological solutions, recycling of reverse waste and expansion of sales areas, which leads to an increase in production and sales of products.

Ionic Liquids at the Electrode Interface: Insights into Surface Passivation and Framework Expansion of Hard Carbon Anodes

Ionic liquids are being extensively explored as an alternative to carbonate-based electrolytes in reversible batteries, as they can exhibit lower flammability and volatility, and better overall safety. The polarity and acidity/basicity of ionic liquids can be tuned to control solubility, and can influence the electrochemical window and interfacial properties when used in batteries. In this study, 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl) imide (EMIM.TFSI) and 1-methyl-1-propypyrrolidinium bis(trifluoromethanesulfonyl)imide (MPPY.TFSI) were selected because they are well-known, relatively stable ionic liquids with large electrochemical windows which show strikingly different behavior with carbonaceous anodes due to differences in interface passivation. High surface area mesoporous hard carbon anodes were employed to provide a large signal from the interfacial chemistry of these electrolytes during reversible cycling. A combination of operando small-angle neutron scattering (SANS) and ex-situ electrochemical studies were used to understand the differences in solid electrolyte interphase (SEI) for these ionic liquids, and the relationship of SEI formation to hard carbon microstructural changes. Reversible hard carbon expansion is observed in the first cycle for the electrolyte lithium bis(trifluoro-methanesulfonyl)imide (LiTFSI)/EMIM.TFSI related to EMIM+ intercalation and deintercalation before a stable SEI is formed, while a largely irreversible framework expansion of 15% is observed for the LiTFSI/MPPY.TFSI electrolyte. There is only relatively minor expansion and contraction in subsequent cycles after a suitable solid electrolyte interphase (SEI) has formed. Irreversible framework expansion in conjunction with SEI formation is found to be essential for the stable cycling of hard carbon electrodes.[1]Acknowledgement: Research was sponsored by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. Research at Spallation Neutron Source user facility was sponsored by the Division of Scientific User Facilities, Office of Basic Energy Sciences, US Department of Energy, under contract DE-AC05-00OR22725 with UT-Battelle, LLC.[1] Bridges, C.A.; Sun, X.G.; Guo, B.K.; Heller, W.T.; He, L.L.; Paranthaman, M.P.; Dai, S. “Observing Framework Expansion of Ordered Mesoporous Hard Carbon Anodes with Ionic Liquid Electrolytes via in Situ Small-Angle Neutron Scattering.” ACS Energy Lett. 2017, 2, (7), 1698-1704.

Silicon Monoxide As Anode Material for Lithium Ion Batteries

Silicon monoxide (SiO) is a very promising anode material for the next generation high energy lithium ion batteries due to its high theoretical specific capacity of 1710 mAh/g and volumetric capacity of 1547 Ah/L.[1] Compared to commercially used graphite, SiO can offer 18% cell stack level improvement in volumetric energy density and 11% in gravimetric energy density (calculated based on the same cell stack model), enabling utilization of smaller and lighter batteries. It also offers more stable cycle performance compared to Si due to less volume change (134% initial volume expansion and 117% reversible volume expansion), making it a more practical choice for lithium ion batteries in the near future.SiO is composed of Si nanodomains in a SiO2 matrix. An interphase region of transitional stoichiometry (SiOx, 0 < x < 2) is also present between Si and SiO2 and takes up 20-25 at.% of the entire composition.[2] During the lithiation and delithiation, the Si nanodomains react reversibly with lithium, similar to amorphous silicon, to give the reversible capacity. The SiO2 matrix reacts irreversibly with lithium to form lithium silicates and lithium oxide. Therefore, the Si domain size and interphase suboxide between Si and SiO2 have effect on the electrochemical performance of SiO. In this study, we gradually changed the microstructure of SiO via annealing treatment and thoroughly studied the change of the SiO microstructure and its impact on the electrochemical performance of the SiO. Together with electrode formulation optimization, up to 99% capacity retention during 50 cycles was obtained in full cells when using pure SiO as anode and LiNi0.5Mn0.3Co0.2O2 as cathode. Acknowledgement We gratefully acknowledge the support from Peter Faguy at the U.S. Department of Energy’s (DOE) office of Energy Efficiency & Renewable Energy (EERE) - Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. Argonne National Laboratory is a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357.Reference: Obrovac, M. N.; Chevrier, V. L., Alloy Negative Electrodes for Li-Ion Batteries. Chemical Reviews 2014, 114 (23), 11444-11502.Hirata, A.; Kohara, S.; Asada, T.; Arao, M.; Yogi, C.; Imai, H.; Tan, Y.; Fujita, T.; Chen, M., Atomic-scale disproportionation in amorphous silicon monoxide. Nature Communications 2016, 7, 11591.

SAUR proteins and PP2C.D phosphatases regulate H+-ATPases and K+ channels to control stomatal movements.

Activation of plasma membrane (PM) H+-ATPase activity is crucial in guard cells to promote light-stimulated stomatal opening, and in growing organs to promote cell expansion. In growing organs, SMALL AUXIN UP RNA (SAUR) proteins inhibit the PP2C.D2, PP2C.D5, and PP2C.D6 (PP2C.D2/5/6) phosphatases, thereby preventing dephosphorylation of the penultimate phosphothreonine of PM H+-ATPases and trapping them in the activated state to promote cell expansion. To elucidate whether SAUR-PP2C.D regulatory modules also affect reversible cell expansion, we examined stomatal apertures and conductances of Arabidopsis thaliana plants with altered SAUR or PP2C.D activity. Here, we report that the pp2c.d2/5/6 triple knockout mutant plants and plant lines overexpressing SAUR fusion proteins exhibit enhanced stomatal apertures and conductances. Reciprocally, saur56 saur60 double mutants, lacking two SAUR genes normally expressed in guard cells, displayed reduced apertures and conductances, as did plants overexpressing PP2C.D5. Although altered PM H+-ATPase activity contributes to these stomatal phenotypes, voltage clamp analysis showed significant changes also in K+ channel gating in lines with altered SAUR and PP2C.D function. Together, our findings demonstrate that SAUR and PP2C.D proteins act antagonistically to facilitate stomatal movements through a concerted targeting of both ATP-dependent H+ pumping and channel-mediated K+ transport.

Flexible C-C Bonds: Reversible Expansion, Contraction, Formation, and Scission of Extremely Elongated Single Bonds.

Since carbon-carbon (C-C) covalent bonds are rigid and robust, the bond length is, in general, nearly constant and depends only on the bond order and hybrid orbitals. We report herein direct visualization of the reversible expansion and contraction of a C(sp3 )-C(sp3 ) single bond by light and heat. This flexibility of a C-C bond was demonstrated by X-ray analysis and Raman spectroscopy of hexaphenylethane (HPE)-type hydrocarbons with two spiro-dibenzocycloheptatriene units, the intramolecular [2+2] photocyclization of which and thermal cleavage of the resulting cyclobutane ring both occur in a single-crystalline phase. The force constant of the contracted C-C bond is 1.6 times greater than that of the expanded bond. Since formation of the cyclobutane ring and contraction of the C-C bond lower the HOMO level by approximately 1 eV, the oxidative properties of these HPEs with a flexible C-C bond can be deactivated/activated by light/heat.

Flexible C−C Bonds: Reversible Expansion, Contraction, Formation, and Scission of Extremely Elongated Single Bonds

AbstractSince carbon–carbon (C−C) covalent bonds are rigid and robust, the bond length is, in general, nearly constant and depends only on the bond order and hybrid orbitals. We report herein direct visualization of the reversible expansion and contraction of a C(sp3)−C(sp3) single bond by light and heat. This flexibility of a C−C bond was demonstrated by X‐ray analysis and Raman spectroscopy of hexaphenylethane (HPE)‐type hydrocarbons with two spiro‐dibenzocycloheptatriene units, the intramolecular [2+2] photocyclization of which and thermal cleavage of the resulting cyclobutane ring both occur in a single‐crystalline phase. The force constant of the contracted C−C bond is 1.6 times greater than that of the expanded bond. Since formation of the cyclobutane ring and contraction of the C−C bond lower the HOMO level by approximately 1 eV, the oxidative properties of these HPEs with a flexible C−C bond can be deactivated/activated by light/heat.