Twisted State Research Articles

When a Twist Makes a Difference: Exploring PCET and ESIPT on a Nonplanar Hydrogen-Bonded Donor-Acceptor System.

Bioinspired benzimidazole-phenol constructs with an intramolecular hydrogen bond connecting the phenol and the benzimidazole have been synthesized to study both proton-coupled electron transfer (PCET) and excited-state intramolecular proton transfer (ESIPT) processes. Strategic incorporation of a methyl group disrupts the coplanarity between the aromatic units, causing a pronounced twist, weakening the intramolecular hydrogen bond, decreasing the phenol redox potential, reducing the chemical reversibility, and quenching the fluorescence emission. Infrared spectroelectrochemistry and transient absorption spectroscopy confirm the formation of the oxidized product upon PCET and probe excited-state relaxation mechanisms, respectively. Density functional theory calculations of redox potentials corroborate the experimental findings. Additionally, time-dependent density functional theory calculations uncover the fluorescence quenching mechanism, showing that the nonradiative twisted intramolecular charge transfer state responsible for fluorescence quenching is more energetically favorable in the methyl-substituted system. Incorporating groups causing steric hindrance expands the design of biomimetic systems capable of performing both PCET and ESIPT.

Roles of ESIPT and TICT in the Photophysical Process of a Ratiometric Fluorescence Sensor for Al3.

Precise detection of Al3+ with the aid of a fluorescence sensor is of fundamental importance in the fields of water pollution control and food safety. A comprehensive understanding of the photophysical process of the sensor as well as its underlying detection mechanism is a precondition for the design of highly efficient sensors. This contribution performs a thorough investigation of the ratiometric fluorescence sensing mechanism of an Al3+ sensor with the aid of density functional theory and time-dependent density functional theory. Two excited-state intramolecular proton transfer (ESIPT) processes are observed on the S1 state potential energy surface, which leads to emission around 565 nm. A twisted intramolecular charge transfer state is observed after one of the ESIPT processes via cis-trans isomerization of the C═N bond. However, the large energy barrier hinders its occurrence, which is quite unusual. Al3+ is found to form three strong coordination bonds with the sensor, which eliminates ESIPT processes and induces a significant blue shift of the emission spectrum to 480 nm. The origination of the sensor's selectivity is also uncovered by investigating the interaction between the sensor and interfering metal ions.

TICT, and Deep-Blue Electroluminescence from Acceptor-Donor-Acceptor Molecules.

Donor-acceptor (D-A) materials based on butterfly-shaped molecules could inhibit exciton-migration-induced quenching due to molecular twist. To explore this attribute towards beneficial photophysical properties, three novel bipolar acceptor-donor-acceptor (A-D-A) molecules with triphenyl triazine end capping along with substitution ortho to the Tröger's base (TB) scaffold varying from H, Me, and F were explored. The installation of H/Me/F imparted an electron push-pull effect with concomitant maneuvering of photophysical properties. On increasing solvent polarity, a remarkable bathochromic shift with a significant decrease in emission efficiency was observed due to the twisted intramolecular charge transfer state (TICT). Emission enhancement in the ethylene glycol-water mixture and diminution in the THF-water mixture further confirmed the existence of TICT states in these TBs. The torsional dynamics in the excited state were also evidenced by the time-dependent density-functional theory (TD-DFT) calculations. Owing to the butterfly architecture of the TB that suppressed TICT, TB-Trzs exhibited a significant blue shift, accompanied by a favorable quantum yield in the solid state. Among the three compounds, Me-TB-Trz exhibited deep-blue photoluminescence and was explored as a dopant in organic light-emitting diodes (OLEDs) to obtain deep-blue electroluminescence of brightness 4128 cdm-2 and CIE coordinates of (0.16, 0.09).

Mix and Match Tuning of the Conformational and Multistate Redox Switching Properties of an Overcrowded Alkene.

Overcrowded alkenes have received considerable attention as versatile structural motifs in a range of optical switches and light-driven unidirectional motors. In contrast, their actuation by electrochemical stimuli remains underexplored, even though this alternative energy input may be preferred in various applications and enables additional control over molecular switching states and properties. While symmetric bistricyclic overcrowded enes (BAEs) containing two identical halves based on either thioxanthene (TX) or acridine (Acr) motifs are known to be reversible conformational redox switches, their redox potentials are generally too high or low, respectively, thereby preventing wider applications. Herein, we demonstrate that the "mixed" TX-Acr switch possesses redox properties that lie between those of its parent symmetric analogs, enabling interconversion between three stable redox and conformational states at mild potentials. This includes the neutral anti-folded, the dicationic orthogonal, and a unique twisted monoradical cation state, the latter of which is only accessible in the case of the mixed TX-Acr switch and in a pathway-dependent manner. Consequently, with this multistate redox switch, a myriad of molecular properties, including geometry, polarity, absorbance, and fluorescence, can be modulated with high fidelity and reversibility between three distinct stable states. More generally, this study highlights the versatility of the "mix and match" approach in rationally designing redox switches with specific (redox) properties, which in turn is expected to enable a myriad of applications ranging from molecular logic and memory to actuators and energy storage systems.

Stability of twisted states in power-law-coupled Kuramoto oscillators on a circle with and without time delay.

Other than the fully synchronized state, a twisted state can also be an equilibrium solution in the Kuramoto model and its variations. In the present work, we explore the stability of the twisted state in Kuramoto oscillators put on a rim of a planar circle in the two-dimensional space in the presence of power-law decaying interaction strength (∼r^{-α} with the distance r) and time delays due to a finite speed of information transfer. For example, our model can phenomenologically mimic a large sports stadium where many people try to sing or clap their hands in unison; the sound intensity decays with the distance and there can exist a time delay proportional to the distance due to the finiteness of sound speed. We first consider the case without the time delay effect and numerically find that stable twisted states emerge when the exponent α exceeds a critical value of α_{c}≈2. In other words, for α<α_{c}, the fully synchronized state, not the twisted state, is the only stable fixed point of the dynamics. In our analytic approach, we also derive an equation for α_{c} and discuss its solutions. In the presence of time delay, we find that it is possible that the synchronized state becomes unstable while twisted states are stable.

Stability of the twisted states in a ring of oscillators interacting with distance-dependent delays

We consider a ring of phase oscillators interacting with distance-dependent time delays in general forms. It is found that the distance-dependent interaction delay is an essential driving mechanism for the twisted state to occur as a generic state. We carry out rigorous stability analysis for the existence and stability of the twisted states along the Ott–Antonsen invariant manifold and derive the exact characteristic equations for the stability conditions for arbitrarily chosen distance-dependent delay function. The complete stability diagrams are illustrated for two types of distance-dependent delay schemes, the propagational and step-wise interaction delays. Our theoretical results are verified using the direct numerical simulations of the model system.

Nonlinear optical response of 1H-indene-based donor-acceptor chromophores. Influence of the higher-lying states on the first hyperpolarizability

The hyperpolarizabilities often fall short of the fundamental quantum limits. However, in case of 5-(diphenylamino)thiophen-2-yl substituted 1H-indene based donor-π-acceptor (D-π-A) chromophores, in spite of the preponderance of twisted intramolecular charge transfer state, we find that the first hyperpolarizability is modulated (limited!) due to the possible interference of the higher-lying excited states of significant oscillator strength with the lower-lying excited state.

Twisted Intramolecular Charge-Transfer State Addition to Electron-Poor Olefins.

When electron-rich arylpyrrolinium salts are irradiated with ultraviolet light in the presence of Michael acceptors, the pyrrolinyl and aryl fragments add to the activated and polarized double bond in a regioselective manner, forming two C-C bonds and fragmenting the substrate. In this paper, we present a model for this intriguing reaction, supported by spectroscopy and computational analyses, and provide evidence for rectifying previously misassigned structures. We postulate that the photochemical reaction is inefficient because the reaction between the twisted intramolecular charge-transfer state and the olefin competes with fluorescence from this state upon photon absorption. We also discuss the practical advantages of performing this photochemical reaction in a continuous flow setup. Additionally, we explore several subsequent reactions that allow us to further modify the products of the photochemical step, ultimately leading to the creation of new chemical structures.

Oxidized Bisindolyl-Based Amphiphilic Probe for Dual Mode Analysis of Heavy Metal Pollutants in Aqueous Medium.

The oxidized bisindolyl-based amphiphilic, chromogenic probe has been synthesized that can form nanoscopic aggregates in the aqueous medium. Along with solvent polarity and pH of the medium, it was observed that the addition of heavy metal pollutants, like Hg2+ can cause significant alteration in the charge transfer state. This resulted in the immediate change in the solution color from yellow to orange. Additionally, we could excite either the monomer species or the aggregates of the probe by choosing the proper excitation wavelength. Upon exciting at 390nm, the compound exhibited a broad fluorescence spectrum with maxima at 450nm, presumably due to twisted state charge transfer. On the contrary, the aggregated species (λex = 465nm) displayed a comparatively weaker fluorescence band centered at 565nm. Interestingly, the fluorescence intensity at the 450nm band experience fluorescence quenching in the presence of Hg2+ ion, while the aggregate emission band remained unaffected. Finally, the present system was utilized for detection of mercury ions in natural water samples.

Twisted 8-Acyl-1-dialkyl-amino-naphthalenes Emit from a Planar Intramolecular Charge Transfer Excited State

Fluorescence from dialkylamino donor–acyl acceptor substituted 1,8-naphthalene derivatives can occur either from a planar (PICT) or a twisted (TICT) intramolecular charge transfer excited state. The photophysical properties of 8-acetyl-1-(dimethyl-amino)naphthalene (3) and 8-pivaloyl-1-(dimethyl-amino)naphthalene (4) are compared with 1-methyl-2,3-dihydronaphtho[1,8-bc]azepin-4(1H)-one (5). In 3 and 4, both the carbonyl and amino groups are forced to twist out of the plane of the naphthalene ring. In 5, these groups are nearly coplanar with the naphthalene. Neither 3 nor 4 fluoresce as strongly as 5, but all three show similar degrees of solvato-chromism and all are strongly quenched by alcohol solvents. Nitrile 6, 8-cyano-1-(dimethyl-amino)naphthalene, does not show the same degree of solvato-chromism as 3–5, nor is it as affected by alcohols. Calculations corroborate the experimental results, indicating that 3–5 emit from a PICT excited state.

Ultrafast excited state relaxation dynamics of pyran-based D-π-A systems: solvent polarity controls the triplet state.

The excited state relaxation dynamics of V-shaped D-π-A systems having 4H-pyranylidene appended barbituric acid as an acceptor and diphenylamine (TPAPBA) and diethyl amine (EAPBA) as donors were investigated using steady-state and time-resolved spectroscopy along with theoretical optimization. The steady-state photophysical characterization exhibited the bathochromic shift of the emission maximum (∼6400 cm-1) and large change in the dipole moment (∼24D) with an increase of solvent polarity, reflecting the occurrence of the intramolecular charge transfer state (ICT) in the excited state. The nanosecond and femtosecond transient absorption spectra of these derivatives in a non-polar solvent, toluene, reveal that the excited state relaxation pathway involving a local excited state (LE) decayed to ICT followed by the formation of a twisted ICT state by conformational relaxation, finally leading to the triplet state. The lack of observation of a triplet state in the polar solvent, acetonitrile, signifies that the relaxation dynamics of V-shaped triads in the excited state are influenced by the polarity of the solvent.

Saturating the one-axis twisting quantum Cramér-Rao bound with a total spin readout

We show that the lowest quantum Cramér-Rao bound achievable in interferometry with a one-axis twisted spin coherent state is saturated by the asymptotic method of moments error of a protocol that uses one call to the one-axis twisting, one call to time-reversed one-axis twisting, and a final total spin measurement (i.e., a twist-untwist protocol). The result is derived by first showing that the metrological phase diagram for one-axis twisting is asymptotically characterized by a single quantum Fisher information value N(N + 1)/2 for all times, then constructing a twist-untwist protocol having a method of moments error that saturates this value. The case of finite-range one-axis twisting is similarly analyzed, and a simple functional form for the metrological phase diagram is found in both the short-range and long-range interaction regimes. Numerical evidence suggests that the finite-range analogues of twist-untwist protocols can exhibit a method of moments error that asymptotically saturates the lowest quantum Cramér-Rao bound achievable in interferometry with finite-range one-axis twisted spin coherent states for all interaction times.

Отклик химических связей никеля на растягивающие деформации кристалла Ni-пиридиндикарбоксамида

We have carried out a theoretic research of plasticity for the coordination and noncovalent bonds modelling uniaxial mechanical deformation of the crystal cell of bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide)-nickel (II) dichloride. For this purpose, we have modeled stretching deformation of the crystal structure along its crystallographic axes using the 3-corrected Hartree-Fock method with the following semi-empirical corrections for the weak interactions (the Grimme correction of dispersion interactions, D3, basis set superposition error removal by the atom-pair wise geomet-rical counterpoise correction, gCP, and correction of short-ranged basis set incompleteness effects, SRB) with the use of periodic boundary conditions. We have concluded that the geometry of bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide complex has high stability to the increased defor-mations. We have carried out the analysis of the bond lengths and dihedral angels within the metal complex, which has shown insignificant changes of bond lengths, in particular, the bond length change is equal to 4.3 % for N…Ni…N and 5.4 % for Ni…O. The conformation straightening ef-fects of one of the N-butylamine chain has been found under the high stretching deformation of the crystal cell (7–8 Å) due to analysis of dihedral angles and the distance between specific atoms of N-butylamine chain that proves the hypothesis about a forced and twisted conformation state of bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide. In addition, we have found the appearance of a cavity and a crack at the last deformation steps (8–10 Å), which is caused by shifts of neighbour-ing metal complexes in relation to each other; it influences the location of chloride ions. It is noteworthy that cavities and cracks are formed regardless of the axis choice along which the ten-sile deformation is modeled. This fact indicates that the crystal should not exhibit elasticity, but rather brittleness.

Clinical and hematological analysis of testicular torsion in children.

Analyze the clinical manifestations, laboratory tests, and imaging data of testicular torsion to provide clinical insights for timely and accurate diagnosis and treatment of testicular torsion. A retrospective analysis was conducted on the clinical data of 67 pediatric patients suspected of testicular torsion, admitted and subjected to surgical exploration from June 2018 to June 2023. Based on whether the torsed testicle was excised during surgery, the patients were divided into orchiectomy group (40 cases) and orchidopexy group (27 cases). Combining clinical symptoms, signs, ultrasound examinations, and laboratory tests, the study aimed to summarize the influencing factors on the onset, diagnosis, and treatment of testicular torsion. The clinical manifestations of all 67 pediatric patients were generally typical. Color Doppler Flow Imaging (CDFI) and surgical exploration were performed for all cases, and the results were consistent. Testicular color doppler ultrasound suggested reduced or absent blood flow, leading to surgical treatment in all cases. All patients had unilateral testicular torsion, with 46 cases (68.66%) on the left side and 21 cases (31.34%) on the right side. Intrafunicular torsion occurred in 60 cases (89.55%), while extrafunicular torsion occurred in 7 cases (10.45%). The onset distribution was as follows: 20 cases in spring, 16 cases in summer, 16 cases in autumn, and 15 cases in winter. Univariate analysis indicated significant statistical differences in age, degree of testicular torsion, duration of symptoms, NEUT, NLR, and occurrence of tunica fluid between the two groups of patients. Multivariate logistic regression analysis showed that the duration of symptoms and the occurrence of hydrocele were independent risk factors for determining testicular viability. Testicular torsion is more common in children and adolescents, with clinical manifestations including scrotal pain, scrotal redness and swelling, abdominal pain, nausea, and vomiting. In the early stages of testicular torsion, inflammatory markers in the blood increase, and preoperative ultrasound indicates hydrocele. This suggests that the testicle is in an early twisted state, with good viability and potential for preservation.

Strong coupling of flow structure and heat transport in liquid metal thermal convection

A typical feature of thermal convection is the formation of large-scale flow (LSF) structures of the order of system size. How this structure affects global heat transport is an important issue in the study of thermal convection. We present an experimental study of the coupling between the flow structure and heat transport in liquid metal convection with different degrees of spatial confinement, characterized by the aspect ratio $\varGamma$ of the convection cell. Combining measurements in two convection cells with $\varGamma =1.0$ and 0.5, the study shows that a large-scale circulation (LSC) transports ${\sim }35\,\%$ more heat than a twisted LSC. It is further found that when the LSF is in the form of the LSC state, the system is in a fully developed turbulence state with a $Nu\sim Ra^{0.29}$ scaling for the heat transport. However, the twisted LSC state with a heat transport scaling of $Nu\sim Ra^{0.37}$ appears when the system is not in the fully developed turbulence state. Bistability is observed when the system evolves from the twisted-LSC-dominated to the LSC-dominated state.

Thioflavin-T: A Quantum Yield-Based Molecular Viscometer for Glycerol-Monohydroxy Alcohol Mixtures.

Molecular rotor dye thioflavin T (ThT) is almost nonfluorescent in low-viscosity solvents but highly fluorescent when bound to amyloid fibrils. This unique property arises from the rotation of the dimethylaniline moiety relative to the benzothiazole moiety in the excited state, which drives the dye from an emissive locally excited state to a twisted intramolecular charge-transfer state. This process is viscosity-controlled, and therefore, we can use the quantum yield of ThT to assess the viscosity of the environment. In this study, we have investigated the quantum yield of ThT (φThT) in various compositions of six alcoholic solvent mixtures of glycerol with methanol, ethanol, n-propanol, iso-propanol, n-butanol, and tert-butanol. We have proposed an empirical model using φThT as a function of the mole fraction of glycerol to estimate the interaction parameters between the components of the solvent mixtures. This analysis allowed us to predict the extent of nonideality of the solvent mixtures. The Förster-Hoffmann- and Loutfy-Arnold-type power law relationship was established between the quantum yield of ThT and bulk viscosity for solvent mixtures of methanol, ethanol, n-butanol, and tert-butanol with glycerol, and it was found to be similar in nature in all the four mixtures. Applying this knowledge, we proposed a methodology to quantify and predict the bulk viscosity coefficient values of several compositions of n-propanol-glycerol and iso-propanol-glycerol mixtures which have not been previously documented.

Multi-stable dye-doped dual-frequency twisted nematic liquid crystal smart window.

In this study, a novel, to the best of our knowledge, dye-doped dual-frequency liquid crystal multi-stable smart window is proposed. A chiral dopant with appropriate content was introduced into dye-doped dual-frequency liquid crystals to achieve an initial 180° twisted state. These liquid crystals can be switched to a nematic phase or a 360° twisted state by controlling the magnitude and frequency of the applied voltage. These nematic phase and 360° twisted states can exist stably for a long time because of the backflow effect and the anisotropic nature of the dual-frequency liquid crystal material. Due to the optical waveguide effect of dye-doped liquid crystals in the long-pitch state, the transmittance was different in nematic phase, 180°, and 360° twisted three zero-field stabilized absorption states. Finally, a multi-stable smart window is developed to switch between three zero-field stabilized absorption and scattering states.

Theoretical reconsideration of the ESPT process of the pheomelanin building block in methanol

Pheomelanin is responsible for enhancing UV sensitivity and its proton transfer (PT) process is crucial to reveal the complex mechanisms of pheomelanin phototoxicity. Nahhas et al. studied the PT process of the pheomelanin building block 6-(2-amino-2-carboxyethyl)-4-hydroxy-1,3-benzothiazole (BT) in methanol. Based on the small Stokes shift corresponding to the absorption and fluorescence peaks, it is deemed that BT cannot perform PT process in methanol [J. Phys. Chem. Lett. 5 (2014) 2094–2100]. However, protic methanol solvent has both oxygen atom that attract proton and hydrogen atom that supply proton. It is worth reconsidering about the intermolecular proton transfer (inter-PT) process of BT with the aid of methanol. In our work, the inter-PT process of BT and methanol molecules are deciphered by density functional theory and time-dependent density functional theory. The structures, non-covalent interactions and infrared spectra testify that the double hydrogen bonds are reinforced under photoexcitation. The potential energy curve of S1 state without barrier attests that the inter-PT process can occur in the BT molecule where methanol acts as the proton transporter. In addition, the fluorescence of BT-methanol complex is emitted by enol* form. In the light of the frontier molecular orbitals, the non-fluorescence of keto* form is explained by the reduced charge coupling compared to the enol* form and the competition of the twisted intramolecular charge transfer state. Our results provide an insight for understanding the photochemical process of the pheomelanin in protic systems.

Spectroscopic studies on the supramolecular interactions of methyl benzoate derivatives with p-sulfocalix[6]arene macrocycles

This paper is a continuation of our previous research and aims to further investigate and elucidate the nature and mechanisms of noncovalent supramolecular interactions between four methyl benzoate derivatives (I-IV), which are capable of exhibiting Twisted Intramolecular Charge Transfer (TICT) and/or Excited State Intramolecular Proton Transfer (ESIPT)‐type behavior, and chemical and biological nanocavities. Photophysical and photochemical properties of molecules I-IV in aqueous solution in the presence of well-recognized macrocyclic host p-sulfocalix[6]arenes (SCA[6]) have been studied using steady-state, time-resolved and 1H NMR spectroscopic techniques. The changes in the ground- and excited-state spectroscopic characteristics (absorption and fluorescence spectra, time-resolved fluorescence spectra, fluorescence decay times and 1H NMR spectra) undergo significant modifications upon encapsulation of the investigated methyl benzoate derivative in the macromolecular cavity. For the two compounds (I and II), the interactions with the macrocycles with a hydrophobic SCA[6] cavity lead to the formation of stable inclusion complexes with 1:1 stoichiometry, both in the ground and excited state, while the stoichiometry of the III-SCA[6] and IV-SCA[6] complexes in the ground and excited states is 1:2. The values of the equilibrium constants have been determined from the spectroscopic data using Benesi-Hildebrand and nonlinear regression procedures. The location of the organic molecule inside the SCA[6] has been investigated by 1H NMR experiments. The changes in macrocyclic compound-induced NMR chemical shifts clearly indicate that the chemical structure of inclusion complexes is very different for methyl benzoate derivative-SCA[6] and methyl benzoate derivative-CB[7] systems. Finally, we have shown, using time-dependent fluorescence Stokes shift, that very fast solvation dynamics of pure water is markedly different from that of the confined water molecule in SCA[6] system.

The radiative surface hopping (RSH) algorithm: Capturing fluorescence events in molecular systems within a semi-classical non-adiabatic molecular dynamics framework.

In this article, we present the radiative surface hopping algorithm, which enables modeling fluorescence within a semi-classical non-adiabatic molecular dynamics framework. The algorithm has been tested for the photodeactivation dynamics of trans-4-dimethylamino-4'-cyanostilbene (DCS). By treating on equal footing the radiative and non-radiative processes, our method allows us to attain a complete molecular movie of the excited-state deactivation. Our dynamics rely on a semi-empirical quantum mechanical/molecular mechanical Hamiltonian and have been run for hundreds of picoseconds, both in the gas phase and in isopropyl ether. The proposed approach successfully captures the first fluorescence processes occurring in DCS, and it succeeds in reproducing the experimental fluorescence lifetime and quantum yield, especially in the polar solvent. The analysis of the geometrical features of the emissive species during the dynamics discards the hypothesis of a twisted intramolecular charge transfer state to be responsible for the dual emission observed experimentally in some polar solvents. In a nutshell, our method opens the way for theoretical studies on early fluorescence events occurring up to hundreds of picoseconds in molecular systems.