T1 Transition Research Articles

Relaxation dynamics in the self-propelled Voronoi model for epithelial monolayers

Cell monolayers and epithelial tissues display slow relaxation dynamics during the reversible transition between mesenchymal and epithelial cells, a phenomenon directly relevant to embryogenesis, tumor metastases, and wound healing. In active cells, persistent motion induces collective dynamics that significantly influence relaxation behavior. To better understand the role of persistence in cell relaxations, we perform extensive simulations and employ cage-relative measures to address the previously overlooked system size effects in model active cells. We identify the glass transition at various persistence values, demonstrating conventional near-equilibrium supercooled dynamics at low persistence. However, highly persistent cells exhibit distinctive intermittent dynamics associated with intermittent local T1 transitions, where cell velocity correlates over space with a characteristic length ξ. More significantly, we formulate a universal relationship predicting the global relaxation time based on the T1 transition and the spatial velocity correlation across a wide range of persistence values. Specifically, the relaxation time demonstrates a power-law dependence on the irreversible T1 transition rate, multiplied by exp(ξ). Here, ξ vanishes at small persistence in nearly equilibrated cells, and the irreversible T1 transition rate diminishes towards the mode-coupling glass transition point. Published by the American Physical Society 2024

From cell intercalation to flow, the importance of T1 transitions

T1 transitions, also called cell intercalations, are important sources of fluidization of epithelial cell monolayers. We use a multiphase field model to quantify this tissue fluidization in terms of the relative dispersion of cells and characterize the T1 flow profile. We show that the ensemble-averaged flow profile of a T1 transition has a saddle-point pattern accompanied by a localized burst in cell speed. Although the temporal evolution of the relative dispersion of cells depends on specific model details, the different dispersion curves collapse robustly onto a linear function of the number of T1 transitions, implying an important connection between T1 transitions and mixing in dense systems. Published by the American Physical Society 2024

Solar overall water-splitting by a spin-hybrid all-organic semiconductor

Direct solar-to-hydrogen conversion from pure water using all-organic heterogeneous catalysts remains elusive. The challenges are twofold: (i) full-band low-frequent photons in the solar spectrum cannot be harnessed into a unified S1 excited state for water-splitting based on the common Kasha-allowed S0 → S1 excitation; (ii) the H+ → H2 evolution suffers the high overpotential on pristine organic surfaces. Here, we report an organic molecular crystal nanobelt through the self-assembly of spin-one open-shell perylene diimide diradical anions (:PDI2-) and their tautomeric spin-zero closed-shell quinoid isomers (PDI2-). The self-assembled :PDI2-/PDI2- crystal nanobelt alters the spin-dependent excitation evolution, leading to spin-allowed S0S1 → 1(TT) → T1 + T1 singlet fission under visible-light (420 nm~700 nm) and a spin-forbidden S0 → T1 transition under near-infrared (700 nm~1100 nm) within spin-hybrid chromophores. With a triplet-triplet annihilation upconversion, a newly formed S1 excited state on the diradical-quinoid hybrid induces the H+ reduction through a favorable hydrophilic diradical-mediated electron transfer, which enables simultaneous H2 and O2 production from pure water with an average apparent quantum yield over 1.5% under the visible to near-infrared solar spectrum.

Graph topological transformations in space-filling cell aggregates.

Cell rearrangements are fundamental mechanisms driving large-scale deformations of living tissues. In three-dimensional (3D) space-filling cell aggregates, cells rearrange through local topological transitions of the network of cell-cell interfaces, which is most conveniently described by the vertex model. Since these transitions are not yet mathematically properly formulated, the 3D vertex model is generally difficult to implement. The few existing implementations rely on highly customized and complex software-engineering solutions, which cannot be transparently delineated and are thus mostly non-reproducible. To solve this outstanding problem, we propose a reformulation of the vertex model. Our approach, called Graph Vertex Model (GVM), is based on storing the topology of the cell network into a knowledge graph with a particular data structure that allows performing cell-rearrangement events by simple graph transformations. Importantly, when these same transformations are applied to a two-dimensional (2D) polygonal cell aggregate, they reduce to a well-known T1 transition, thereby generalizing cell-rearrangements in 2D and 3D space-filling packings. This result suggests that the GVM's graph data structure may be the most natural representation of cell aggregates and tissues. We also develop a Python package that implements GVM, relying on a graph-database-management framework Neo4j. We use this package to characterize an order-disorder transition in 3D cell aggregates, driven by active noise and we find aggregates undergoing efficient ordering close to the transition point. In all, our work showcases knowledge graphs as particularly suitable data models for structured storage, analysis, and manipulation of tissue data.

Določanje obstojnosti funkcionaliziranih tekstilij na osnovi kopolimerov akrilonitrila na toplotno in toplotno-oksidativno razgradnjo

Acrylonitrile is widely used to produce carbon fibres, household textiles, artificial fur, etc. The modification of polyacrylonitrile fibres in an alkaline medium is extended in the production of textile sorbents. The scientific direction of fibre modification through surface activation using hydrogen peroxide is of scientific interest. However, the thermal and thermophysical properties of the samples are not examined. Therefore, interest arises when analysing the effect of polyacrylonitrile textile material functionalization on the resistance of fibres to thermal oxidation and thermal degradation. The study of thermogravimetry and differential thermogravimetry thermooxide of polyacrylonitrile – modified fibres is carried out using thermogravimetric analysis to research the thermal oxidation and thermal degradation of modified polyacrylonitrile fibre samples. A change in the rate of thermal oxidative-degradation in the process of functionalization was identified in this research. A change in the loss of mass of the sample under different conditions of functionalization was also identified. The total glass transition of the polyacrylonitrile was achieved by heating the polymer to 130 °C. The intensification self-regulation of the structure of the polymeric material through the formation of the mesophase was released at the temperature of around 100 °C. During the heating of the initial polyacrylonitrile textile material to the temperature of 70‒80 °C, a weakening of intermolecular contacts was observed, which led to an increase in the mobility of macromolecular segments. The temperature of 78 °С was considered to be the initial glass transition temperature Tg,t1 and Tg,t2 – 121 °С as the final temperature for the original sample. However, if the temperature exceeded 130 °C, chemical changes in the polymer occurred, in particular, the process of cyclization. The analysis of the thermogravimetry data of thermally oxidized samples resulted in the retention of the complex stepwise nature of decomposition inherent in the initial fibrous material based on acrylonitrile copolymers. The conducted analysis showed the absence of significant changes in the reasonable conditions of chemical modification and practical operation of textile materials. The physical and mechanical properties of functionalized textile materials based on acrylonitrile copolymers were studied. As a result of surface functionalization, an insignificant strength reduction of functionalized textile materials occurred.

Investigation of Electronic Structures of Triplet States Using Step-Scan Time-Resolved Fourier-Transform Near-Infrared Spectroscopy.

Triplet transitions of light-emitting materials, including rose bengal, tris(2-phenylpyridine)iridium(III) [Ir(ppy)3], tris(1-phenylisoquinoline)iridium(III) [Ir(piq)3], and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic), were studied using step-scan time-resolved Fourier-transform near-infrared spectroscopy. The samples were excited to their singlet excited states by a 355 nm laser and then underwent efficient conversions/crossings to their triplet manifolds. For rose bengal, a transient absorption band appeared at 9400 cm-1, attributed to the T3 ← T1 transition based on the corresponding time evolution and the theoretical calculations. For Ir(ppy)3, Ir(piq)3, and FIrpic, the most intense bands were observed at 7700, 7500, and 7500 cm-1 and assigned to T7 ← T1, T6 ← T1, and T6 ← T1 transitions, respectively. For Ir(ppy)3, the most intense band involved transitions between different triplet metal-to-ligand charge transfer (3MLCT) states, while for Ir(piq)3 and FIrpic, they involved a metal center to 3MLCT transition. These T1 states were assigned to 3MLCT.

In-depth study of structural, magnetic and XPS behavior of the double perovskite La2-xCex/2Erx/2NiMnO6

Structural, morphological, X-ray photoelectron spectroscopy (XPS) and magnetic details of La2-xCex/2Erx/2NiMnO6 (x = 0.00 and 0.025) prepared by the traditional ceramic method were investigated. X ray-diffraction refinements by Rietveld method indicate that our samples have a monoclinic system with the space group P 21/n No. (14). A small amount of MnNi6O8 impurity was detected in both samples. Morphological analysis reveals that our samples contain grains of different sizes equal to 1.249 µm and 1.260 µm for x = 0.00 and 0.025. Mapping and EDX analysis confirm the existence and homogeneous distribution of elements on the surface of our samples. According to the x-ray photoelectron spectroscopy (XPS) analysis, the presence of a trivalent oxidation state La and RE ions, along with a mixed-valence state of Ni and Mn ions, has been confirmed in the samples. For magnetic analysis, a double transition temperature is detected from the dM/dT variation for the FC curve. The initial transition (T1) occurs at lower temperatures, approximately 105 K and 110 K for x = 0.00 and x = 0.025, respectively. On the other hand, the second transition T2 (Tc) takes place at higher temperatures, around 250 K and 265 K, respectively, for x = 0.00 and x = 0.025. These two magnetic transition temperatures are attributed to distinct spin states of Mn and Ni cations. Thus, the low-temperature transition (T1) can be attributed to a vibronic super-exchange interaction involving trivalent oxidation states, specifically Ni3+–O–Mn3+. The higher temperature transition T2 (Tc) was defined as the Curie temperature when the system undergoes a transition from the ferromagnetic (FM) to the paramagnetic state (PM). The magnetocaloric effect (MCE) exhibits the presence of two prominent peaks. The first one is at low temperature around 80 K. The second is at high temperature around 250 K. A phonemological approach called Landau theory was used to deduce the variation of the magnetic entropy (-ΔSM). Good agreement is obtained between the experimental behavior of (- ΔSM) and that predicted by this theory.

Continuum theory for confluent cell monolayers: Interplay between cell growth, division, and intercalation

Mechanical forces generated by dynamic cellular activities play a crucial role in the morphogenesis and growth of biological tissues. While the influence of mechanics is clear, many questions arise regarding the way by which mechanical forces communicate with biological processes at the level of a confluent cell population. Some answers may be found in the development of mathematical models that are capable of describing the emerging behavior of a large population of active agents based on individualistic rules (single-cell response). In this perspective, the present work presents a continuum-scale model that can capture, in an average sense, the active mechanics and evolution of a confluent tissue with or without external mechanical constraints. For this, we conceptualize a confluent cell population (in a monolayer) as a deformable dynamic network, where a single cell can modify the topology of its neighborhood by swapping neighbors or dividing. With this description, we use concepts from statistical mechanics and the transient network theory to derive an equivalent active visco-elastic continuum model, which can recapitulate some of the salient features of the underlying network at the macroscale. Without loss of generality, the cell network is here assumed to follow well-known rules used in vertex model simulations, which are: (a) cell elasticity based on its bulk and cortical elasticity, (b) cell intercalation (or T1 transition), and (c) cell proliferation (expansion and division). We show, through examples and illustrations, that the model is able to characterize complex cross-talk between mechanical forces and biological processes, which are likely to drive the emergent growth and deformation of cell aggregates.

Photosensitizing Metasurface Empowered by Enhanced Magnetic Field of Toroidal Dipole Resonance.

Photochemical reaction exploiting an excited triplet state (T1 ) of a molecule requires two steps for the excitation, i.e., electronic transition from the ground (S0 ) to singlet excited (S1 ) states and intersystem crossing to the T1 state. A dielectric metasurface coupled with photosensitizer that enables energy efficient photochemical reaction via the enhanced S0 →T1 magnetic dipole transition is developed. In the direct S0 →T1 transition, the photon energy of several hundreds of meV is saved compared to the conventional S0 → S1 →T1 transition. To maximize the magnetic field intensity on the surface, a silicon (Si) nanodisk array metasurface with toroidal dipole resonances is designed. The surface of the metasurface is functionalized with ruthenium (Ru(II)) complexes that work as a photosensitizer for singlet oxygen generation. In the coupled system, the rate of the direct S0 →T1 transition of Ru(II) complexes is 41-fold enhanced at the toroidal dipole resonance of a Si nanodisk array. The enhancement of a singlet oxygen generation rate is observed when the toroidal dipole resonance of a Si nanodisk array is matched with the direct S0 →T1 transition wavelength of Ru(II) complexes.

Robust statistical properties of T1 transitions in a multi-phase field model of cell monolayers

Large-scale tissue deformation which is fundamental to tissue development hinges on local cellular rearrangements, such as T1 transitions. In the realm of the multi-phase field model, we analyse the statistical and dynamical properties of T1 transitions in a confluent monolayer. We identify an energy profile that is robust to changes in several model parameters. It is characterized by an asymmetric profile with a fast increase in energy before the T1 transition and a sudden drop after the T1 transition, followed by a slow relaxation. The latter being a signature of the fluidity of the cell monolayer. We show that T1 transitions are sources of localised large deformation of the cells undergoing the neighbour exchange, and they induce other T1 transitions in the nearby cells leading to a chaining of events that propagate local cell deformation to large scale tissue flows.

Size-dependent response of cells in epithelial tissue modulated by contractile stress fibers

Although cells with distinct apical areas have been widely observed in epithelial tissues, how the size of cells affects their behavior during tissue deformation and morphogenesis as well as key physical factors modulating such influence remains elusive. Here, we showed that the elongation of cells within the monolayer under anisotropic biaxial stretching increases with their size because the strain released by local cell rearrangement (i.e., T1 transition) is more significant for small cells that possess higher contractility. On the other hand, by incorporating the nucleation, peeling, merging, and breakage dynamics of subcellular stress fibers into classical vertex formulation, we found that stress fibers with orientations predominantly aligned with the main stretching direction will be formed at tricellular junctions, in good agreement with recent experiments. The contractile forces generated by stress fibers help cells to resist imposed stretching, reduce the occurrence of T1 transitions, and, consequently, modulate their size-dependent elongation. Our findings demonstrate that epithelial cells could utilize their size and internal structure to regulate their physical and related biological behaviors. The theoretical framework proposed here can also be extended to investigate the roles of cell geometry and intracellular contraction in processes such as collective cell migration and embryo development.

Room Temperature Phosphorescence of 5,6-Benzoquinoline

Phosphorescence emission of 5,6-Benzoquinoline embedded in poly (vinyl alcohol) film has been studied at room temperature. A strong green long-lived emission was observed in films doped with 5,6-Benzoquinoline while illuminated on a UV plate. A broad phosphorescence emission spectrum is centered at about 500 nm. The phosphorescence excitation spectrum follows the absorption spectrum of 5,6-Benzoquinoline, except for a long-wavelength part, which is well beyond the absorption band. This long-wavelength part of the absorption spectrum is responsible for the forbidden S0—T1 transition. The excitation at 430 nm resulted in the long-lived emission with a spectrum similar to the phosphorescence spectrum obtained with UV excitation within the absorption of 5,6-Benzoquinoline. The phosphorescence anisotropy obtained with a direct S0—T1 excitation is positive, while the UV excitation is negative. In contrast to fluorescence, the phosphorescence intensity strongly depends on temperature. Phosphorescence lifetimes with UV and long-wavelength excitation are similar, with a mean value of about 0.5 s.

Modulation of Intersystem Crossing by Chemical Composition and Solvent Effects: Benzophenone, Anthrone and Fluorenone

AbstractCombined density functional theory and multireference configuration interaction methods including spin‐orbit coupling and spin‐vibronic interactions have been used to elucidate the photophysical pathways of benzophenone (BP), anthrone (A) and fluorenone (FL). Our results reveal that the slower S1(1nπ*) T1(3ππ*) passage of FL in the gas phase, as compared to BP and A, originates from the different electronic structures of the T1(3ππ*) states in these compounds and is not related to the planarity of the nuclear arrangement. Temperature effects on the rate constants of intersystem‐crossing (ISC), reverse ISC (rISC) and fluorescence have been investigated for FL in solvents of different polarity. Experimentally observed trends for rate constants are well reproduced. A nearly temperature‐ and solvent‐independent, slower down‐hill ISC component is attributed to the El‐Sayed‐forbidden S1(1ππ*) T1(3ππ*) transition in these environments. The faster El‐Sayed‐allowed S1(1ππ*) T2(3nπ*) ISC requires thermal activation in tetrahydrofuran and acetonitrile solution so that fluorescence may compete against triplet formation. In cyclohexane solution, S1(1ππ*) and T2(3nπ*) are nearly degenerate according to our calculations. Hence S1 T2 ISC and S1 T2 rISC have similar rate constants. If T2 T1 internal conversion could be slowed down by deuteration or perfluorination, for example, FL‐derivatives might show delayed fluorescence.

Vibrational spectroscopy, electrical, and thermal properties of [N (CH3)4][N(C2H5)4]CoCl4 compound

Abstract[N (CH3)4][N(C2H5)4]CoCl4 new hybrid compound was synthesized by slow evaporation at room temperature. The X‐ray powder diffraction indicates that this material has an orthorhombic structure with P212121 space group. Two endothermic peaks at T1 = 293 K and T2 = 387 K are observed by differential scanning calorimetric. The real and imaginary parts of the permittivity as function of temperature shows the ferroelectric phase below T = 288 K. The Nyquist diagrams are simulated based on the equivalent circuit chosen by the Z‐View‐software and show the contribution of the grain and electrodes effect. Raman spectroscopy study at room temperature confirms the composition of the synthesized compound. Furthermore, the ferroelectric–paraelectric phase transition T1 is demonstrated by temperature‐dependent Raman spectroscopic studies.

Improving the chemical stability of blue heteroleptic iridium emitter FIrpic in the lowest triplet state through ancillary ligand modification: a theoretical perspective.

With the aim of providing a deeper understanding of the underlying degradation mechanisms associated with the lifetime of blue emitters during the decay process of blue PhOLEDs, quantum chemistry studies were performed to examine the chemical degradation mechanism of common sky blue emitter iridium(III)bis(4,6-di-fluorophenyl)-pyridinato-N,C2')picolinate (FIrpic) and its derivatives with density functional theory (DFT) calculations. For these Ir(III) emitters, the Ir-N1 bond between the ancillary ligand (picolinate) and central iridium will be broken by external light stimuli, which is followed by conversion from the initial emissive metal-to-ligand charge transfer (3MLCT) state to the non-emissive metal centered (3MC) state. The potential energy change for the photo-induced degradation path is then dominated by the energy levels of the 3MT and 3MC states, which are related to the triplet transition energy and the Ir-N1 bond strength, respectively. Thereby, the Ir-N1 bond dissociation in the lowest triplet state will be much harder to proceed if the S0 → T1 transition energy gets more energetically stable or the bond strength gets larger. It is believed that strategic modification of the ancillary ligand, especially by substitution of electron-donating groups at the para position of the pyridyl N atom or extension of the p-electron delocalization, is an effective and easy way to enhance the photochemical stability of the typical blue emitter FIrpic.

Direct Excitation of Triplet State of Molecule by Enhanced Magnetic Field of Dielectric Metasurfaces.

Efficient excitation of a triplet (T1 ) state of a molecule has far-reaching effects on photochemical reaction and energy conversion systems. Because the optical transition from a ground singlet (S0 ) to a T1 state is spin-forbidden, a T1 state is generated via intersystem crossing (ISC) from an excited singlet (S1 ) state. Although the excitation efficiency of a T1 state can be increased by enhancing ISC utilizing a heavy atom effect, energy loss during S1 →T1 relaxation is inevitable. Here, a general approach to directly excite a T1 state from a ground S0 state via magnetic dipole transition, which is boosted by enhanced magnetic field induced by a dielectric metasurface, is proposed. As a dielectric metasurface, a hexagonal array of silicon (Si) nanodisks is employed; the nanodisk array induces a strongly enhanced magnetic field on the surface due to the toroidal dipole (TD) resonance. A proof-of-concept experiment is performed using ruthenium (Ru) complexes placed on a metasurface and demonstrates that the phosphorescence is 35-fold enhanced on a metasurface when the TD resonance is tuned to the wavelength of the direct S0 →T1 transition. These results indicate that photon energy necessary to excite the T1 state can be reduced by more than 400 meV compared to the process involving the ISC. By combining optical measurements with numerical simulations, the mechanism of the phosphorescence enhancement is quantitatively discussed.

A theory of localized excitations in supercooled liquids.

A new connection between the structure and dynamics in glass-forming liquids is presented. We show how the origin of spatially localized excitations, as defined by the dynamical facilitation (DF) theory, can be understood from a structure-based framework. This framework is constructed by associating excitation events in the DF theory to hopping events between energy minima in the potential energy landscape (PEL). By reducing the PEL to an equal energy well picture and applying a harmonic approximation, we develop a field theory to describe elastic fluctuations about inherent states, which are energy minimizing configurations of the PEL. We model an excitation as a shear transformation zone (STZ) inducing a localized pure shear deformation onto an inherent state. We connect STZs to T1 transition events that break the elastic bonds holding the local structure of an inherent state. A formula for the excitation energy barrier, denoted as Jσ, is obtained as a function of inherent-state elastic moduli and the radial distribution function. The energy barrier from the current theory is compared to the one predicted by the DF theory where good agreement is found in various two-dimensional continuous poly-disperse atomistic models of glass formers. These results strengthen the role of structure and elasticity in driving glassy dynamics through the creation and relaxation of localized excitations.

Effect of Listening Biographies on Frequency Following Response Responses of Vocalists, Violinists, and Non-Musicians to Indian Carnatic Music Stimuli.

Background and ObjectivesThe current study investigates pitch coding using frequency following response (FFR) among vocalists, violinists, and non-musicians for Indian Carnatic transition music stimuli and assesses whether their listening biographies strengthen their F0 neural encoding for these stimuli.Subjects and MethodsThree participant groups in the age range of 18-45 years were included in the study. The first group of participants consisted of 20 trained Carnatic vocalists, the second group consisted of 13 trained violinists, and the third group consisted of 22 non-musicians. The stimuli consisted of three Indian Carnatic raga notes (/S-R2-G3/), which was sung by a trained vocalist and played by a trained violinist. For the purposes of this study, the two transitions between the notes T1=/S-R2/ and T2=/R2-G3/ were analyzed, and FFRs were recorded binaurally at 80 dB SPL using neuroscan equipment.ResultsOverall average responses of the participants were generated. To assess the participants’ pitch tracking to the Carnatic music stimuli, stimulus to response correlation (CC), pitch strength (PS), and pitch error (PE) were measured. Results revealed that both the vocalists and violinists had better CC and PS values with lower PE values, as compared to non-musicians, for both vocal and violin T1 and T2 transition stimuli. Between the musician groups, the vocalists were found to perform superiorly to the violinists for both vocal and violin T1 and T2 transition stimuli.ConclusionsListening biographies strengthened F0 neural coding, with respect to the vocalists for vocal stimulus at the brainstem level. The violinists, on the other hand, did not show such preference.

Singlet Fission in Terrylenediimide Single Crystals: Competition between Biexciton Annihilation and Free Triplet Exciton Formation

Understanding singlet fission (SF) is an important strategy for extending the power conversion efficiency of next-generation solar cells beyond the Shockley–Queisser limit. Thus far, most studies of SF have focused on polycrystalline films, whose heterogeneity often makes it difficult to probe the electronic states involved in the formation of the correlated triplet biexciton state, 1(T1T1), and its decorrelation into free triplet excitons. Polarization-resolved, femtosecond transient absorption microscopy of a 1,6,9,14-tetraphenylterrylene-3,4:11,13-bis(dicarboximide) (Ph4TDI) single crystal reveals the formation of transient spectra in <200 fs having features characteristic of 1(T1T1), 1(S1S0), and Ph4TDI•+-Ph4TDI•– charge-transfer (CT) states. This indicates that either an ultrafast equilibrium between these states occurs or that the initially formed biexciton state is a mixture of these states. This spectrum evolves in time to give the Tn ← T1 spectrum of the free triplet excitons. We show further that this initially formed state has its optical transition polarized nearly perpendicular to that of the Tn ← T1 transition in the free triplet excitons. This indicates that the observed free triplet excitons have migrated from the π-stacked Ph4TDI columns where the 1(T1T1) state is produced to neighboring, nearly orthogonal π-stacked Ph4TDI columns, resulting in a weaker electronic interaction between the free triplet excitons essential to extending their lifetimes. However, the mobility of the 1(T1T1) state in the Ph4TDI π-stacking direction results in significant annihilation of biexciton pairs limiting the yield of free triplet excitons to about 60%.

Dual-Responsive Thermally Activated Delayed Fluorescence of Spiropyran Derivatives

Dual-Responsive Thermally Activated Delayed Fluorescence of Spiropyran Derivatives