Di-benzoquinone Cyclopentadithiophene Diradicaloids Show Spin-States Optical Transitions and Anomalous NIR Emission.

We have prepared a series of bis(semiquinone) compounds with dithiophene bridges of different length that evolve from closed-shell to full diradical character on the basis of the narrow singlet-triplet energy gaps which allows the triplet population at 298 K for the longer compound. The medium size compound has a variety of photonic properties with absorptions and emission in the true NIR region mediated by a unique case of antikasha emission. A whole set of optical absorption and emission steady state and pico-second transient absorption spectroscopies together with vibrational spectroscopies, spectroelectrochemistry and theoretical calculations have been carried our and subsequently interpreted.

Efficient near-infrared organic light-emitting diodes with emission from spin doublet excitons.

The development of luminescent organic radicals has resulted in materials with excellent optical properties for near-infrared emission. Applications of light generation in this range span from bioimaging to surveillance. Although the unpaired electron arrangements of radicals enable efficient radiative transitions within the doublet-spin manifold in organic light-emitting diodes, their performance is limited by non-radiative pathways introduced in electroluminescence. Here we present a host-guest design for organic light-emitting diodes that exploits energy transfer with up to 9.6% external quantum efficiency for 800 nm emission. The tris(2,4,6-trichlorophenyl)methyl-triphenyl-amine radical guest is energy-matched to the triplet state in a charge-transporting anthracene-derivative host. We show from optical spectroscopy and quantum-chemical modelling that reversible host-guest triplet-doublet energy transfer allows efficient harvesting of host triplet excitons.

Effects of Age in Fecal Microbiota and Correlations with Blood Parameters in Genetic Nucleus of Cattle.

This study aimed to determine the impact of age on the fecal microbiota in the genetic nucleus of cattle, with a focus on microbial richness, composition, functional diversity, and correlations with blood parameters. Fecal and blood samples from 21 cattle were analyzed using 16S rRNA gene sequencing. Older cattle exhibited greater bacterial diversity and abundance, with significant changes in alpha diversity indices (p < 0.05). Beta diversity analysis revealed significant variations in microbial composition between age groups and the interaction of age and sex (p < 0.05). Correlations between alpha diversity, community composition, and hematological values highlighted the influence of microbiota on bovine health. Beneficial butyrate-producing bacteria, such as Ruminococcaceae, were more abundant in older cattle, suggesting a role in gut health. Functional diversity analysis indicated that younger cattle had significantly more abundant metabolic pathways in fermentation and anaerobic chemoheterotrophy. These findings suggest management strategies including tailored probiotic therapies, dietary adjustments, and targeted health monitoring to enhance livestock health and performance. Further research should include comprehensive metabolic analyses to better correlate microbiota changes with age-related variations, enhancing understanding of the complex interactions between microbiota, age, and reproductive status.

Predictive Guidelines for Electrocyclization of Dithienylethenes.

Molecular photoswitches undergo a structural transformation upon photoexcitation to interconvert between two or more stable forms. In some cases, the structural rearrangement involves the transition between ring-open and ring-closed forms. In this work, we develop simple guidelines for the design of organic molecules able to undergo photochemical electrocyclization, using electronic structure calculations on dithienylethene (DTE)-based compounds. We conclude that the ability to photocyclize can be predicted from the localization and symmetry of frontier molecular orbitals. These ideas are based on the Woodward-Hoffmann rules but go beyond them, allowing us to address a more general family of chromophores. Our methodology has been experimentally validated in a novel series of quinoline-based DTEs, where the ability for photocyclization depends on specific chemical modifications. We use the DTE scaffold as the workhorse model in our study; however, these simple yet powerful guidelines are expected to be generally valid to guide the design of other diarylethenes.

Physically Motivated Improvements of Variational Quantum Eigensolvers.

The adaptive derivative-assembled pseudo-Trotter variational quantum eigensolver (ADAPT-VQE) has emerged as a pivotal promising approach for electronic structure challenges in quantum chemistry with noisy quantum devices. Nevertheless, to surmount existing technological constraints, this study endeavors to enhance ADAPT-VQE's efficacy. Leveraging insights from the electronic structure theory, we concentrate on optimizing state preparation without added computational burden and guiding ansatz expansion to yield more concise wave functions with expedited convergence toward exact solutions. These advancements culminate in shallower circuits and, as demonstrated, reduced measurement requirements. This research delineates these enhancements and assesses their performance across mono, di, and tridimensional arrangements of H4 models, as well as in the water molecule. Ultimately, this work attests to the viability of physically motivated strategies in fortifying ADAPT-VQE's efficiency, marking a significant stride in quantum chemistry simulations.

Electronic Couplings for Triplet-Triplet Annihilation Upconversion in Crystal Rubrene.

Triplet-triplet annihilation photon upconversion (TTA-UC) is a process able to repackage two low-frequency photons into light of higher energy. This transformation is typically orchestrated by the electronic degrees of freedom within organic compounds possessing suitable singlet and triplet energies and electronic couplings. In this work, we propose a computational protocol for the assessment of electronic couplings crucial to TTA-UC in molecular materials and apply it to the study of crystal rubrene. Our methodology integrates sophisticated yet computationally affordable approaches to quantify couplings in singlet and triplet energy transfer, the binding of triplet pairs, and the fusion to the singlet exciton. Of particular significance is the role played by charge-transfer states along the b-axis of rubrene crystal, acting as both partial quenchers of singlet energy transfer and mediators of triplet fusion. Our calculations identify the π-stacking direction as holding notable triplet energy transfer couplings, consistent with the experimentally observed anisotropic exciton diffusion. Finally, we have characterized the impact of thermally induced structural distortions, revealing their key role in the viability of triplet fusion and singlet fission. We posit that our approaches are transferable to a broad spectrum of organic molecular materials, offering a feasible means to quantify electronic couplings.

Reverse intersystem crossing mechanisms in doped triangulenes.

Thermally activated delayed fluorescence (TADF) has emerged as one of the most promising strategies in the quest for organic light emitting diodes with optimal performance. This computational study dissects the mechanistic intricacies of the central photophysical step, reverse intersystem crossing (rISC) in N and B doped triangulenes as potential multi-resonance TADF compounds. Optimal molecular patterns conducive to efficient rISC, encompassing dopant atom size, number, and distribution, are identified. Additionally, we assess various electronic structure methods for characterizing TADF-relevant molecular systems. The findings identify the distinct role of the direct and mediated mechanisms in rISC, and provide insights into the design of advanced TADF chromophores for next-generation OLED technology.

Photocatalytic activity of dual defect modified graphitic carbon nitride is robust to tautomerism: machine learning assisted ab initio quantum dynamics.

Two-dimensional graphitic carbon nitride (GCN) is a popular metal-free polymer for sustainable energy applications due to its unique structure and semiconductor properties. Dopants and defects are used to tune GCN, and dual defect modified GCN exhibits superior properties and enhanced photocatalytic efficiency in comparison to pristine or single defect GCN. We employ a multistep approach combining time-dependent density functional theory and nonadiabatic molecular dynamics (NAMD) with machine learning (ML) to investigate coupled structural and electronic dynamics in GCN over a nanosecond timescale, comparable to and exceeding the lifetimes of photo-generated charge carriers and photocatalytic events. Although frequent hydrogen hopping transitions occur among four tautomeric structures, the electron-hole separation and recombination processes are only weakly sensitive to the tautomerism. The charge separated state survives for about 10 ps, sufficiently long to enable photocatalysis. The employed ML-NAMD methodology provides insights into rare events that can influence excited state dynamics in the condensed phase and nanoscale materials and extends NAMD simulations from pico- to nanoseconds. The ab initio quantum dynamics simulation provides a detailed atomistic mechanism of photoinduced evolution of charge carriers in GCN and rationalizes how GCN remains photo-catalytically active despite its multiple isomeric and tautomeric forms.

3,4-Dimethylenecyclobutene: A Building Block for Design of Macrocycles with Excited State Aromatic Low-Lying High-Spin States.

3,4-Dimethylenecyclobutene (DMCB) is an unusual isomer of benzene. Motivated by recent synthetic progress to substituted derivatives of this scaffold, we carried out a theoretical and computational analysis with a particular focus on the extent of (anti)aromatic character in the lowest excited states of different multiplicities. We found that the parent DMCB is non-aromatic in its singlet ground state (S0), lowest triplet state (T1), and lowest singlet excited state (S1), while it is aromatic in its lowest quintet state (Q1) as this state is represented by a triplet multiplicity cyclobutadiene (CBD) ring and two uncoupled same-spin methylene radicals. Interestingly, the Q1 state, despite having four unpaired electrons, is placed merely 4.8 eV above S0, and there is a corresponding singlet tetraradical 0.16 eV above. The DMCB is potentially a highly useful structural motif for the design of larger molecular entities with interesting optoelectronic properties. Here, we designed macrocycles composed of fused DMCB units, and according to our computations, two of these have low-lying nonet states (i. e., octaradical states) at energies merely 2.40 and 0.37 eV above their S0 states as a result of local Hückel- and Baird-aromatic character of individual 6π- and 4π-electron monocycles.

Enhanced Charge Separation in Single Atom Cobalt Based Graphitic Carbon Nitride: Time Domain Ab Initio Analysis.

In recent years, single atom catalysts have been at the forefront of energy conversion research, particularly in the field of catalysis. Carbon nitrides offer great potential as hosts for stabilizing metal atoms due to their unique electronic structure. We use ab initio nonadiabatic molecular dynamics to study photoexcitation dynamics in single atom cobalt based graphitic carbon nitride. The results elucidate the positive effect of the doped cobalt atom on the electronic structure of GCN. Cobalt doping produces filled midgap states that serve as oxidation centers, advantageous for various redox reactions. The presence of midgap states enables the harvesting of longer wavelength photons, thereby extending the absorption range of solar light. Although doping accelerates charge relaxation overall, charge recombination is significantly slower than charge separation, creating beneficial conditions for catalysis applications. The simulations reveal the detailed microscopic mechanism underlying the improved performance of the doped system due to atomic defects and demonstrate an effective charge separation strategy to construct highly efficient and stable photocatalytic two-dimensional materials.

Incidence of urinary incontinence after hip fracture surgery and associated risk factors: a prospective study.

BACKGROUND: The contribution of the postoperative process to developing or worsening urinary incontinence (UI) after hip fracture surgery (HFS) remains unclear. We aimed to evaluate UI incidence and worsening among older patients undergoing HFS, and explore associated risk factors. METHODS: This prospective cohort study included patients ≥ 75 years admitted between October 2019 and October 2021 to the Traumatology Service of three hospitals in the Consorci Sanitari de Alt-Penedès i Garraf (Barcelona, Spain) with hip fracture requiring surgical treatment. UI was assessed using the first two questions of the International Consultation on Incontinence Questionnaire - Short Form (ICIQ-SF) at baseline and at days 30 (± 3 days) and 90 (± 3 days) after HFS. Surgery-related data and post-surgical complications were recorded. RESULTS: A total of 248 patients with a mean (SD) age of 85.8 (6.78) years were included; 77.8% were female and 154 (62.1%) had UI at baseline. After HFS, 3.24% experienced urinary tract infections (UTIs), 3.64%, acute urinary retention (AUR), 8.57%, constipation, and 53.9%, prolonged catheterization (> 24 h). Fifty-eight patients without baseline UI developed UI at 30 days, resulting in a UI incidence of 61.7% (95% CI 51.1-71.54) between days 0 and 30. Of the 248 patients, 146 (59.1%) experienced worsening of UI. AUR and UTIs were identified as risk factors for UI development and worsening after HFS, respectively. CONCLUSION: The incidence of UI in older patients after HFS is significant. Patient management protocols should consider AUR and UTIs to reduce or eliminate the incidence of UI in older patients undergoing HFS.

Small-Occupation Density Functional Correlation Energy Correction to Wave Function Approximations.

In this work, we introduce a novel hybrid approach, termed WFT-soDFT, designed to seamlessly incorporate DFT correlation into wave function ansatzes. This is achieved through a partitioning of the orbital space, distinguishing between large and small natural occupation numbers associated with wave function theory (WFT) and DFT correlation, respectively. The method uses a novel criterion for partitioning the orbital space and mapping the electron density in natural orbitals with a small occupation with the correlation energy of fast electrons within the homogeneous electron gas. Central to our approach is the introduction of a separation parameter ν, the choice of the WFT approach, and the correlation functional. Here, we combine the RASCI wave function with hole and particle truncation with a local density correlation functional to only account for small-occupation correlation energy. We investigate the performance of the method in the study of small but challenging chemical systems, for which WFT-soDFT demonstrates notable improvements over pristine wave function calculations. These findings collectively highlight the potential of the WFT-soDFT approach as a computationally affordable strategy to improve the accuracy of WFT electronic structure calculations.

Second-order nonlinear optical properties of X-shaped pyrazine derivatives.

This work reports an investigation of the second-order NLO properties of two isomer series of X-shaped pyrazine derivatives, by means of HRS measurements and DFT calculations. The systems differ in the relative position of the donor and acceptor substituents with respect to the axis formed by the nitrogen atoms of the central pyrazine ring. Although the magnitude of the second harmonic signal is similar, HRS measurements revealed that the anisotropy of the NLO response strongly differs in the two chromophore series, the one of the 2,3-isomers being strikingly dipolar, while the one of the 2,6-isomers is mostly octupolar. The experimental observations are well supported by DFT calculations. In particular, the sum-over-states approach allows us to rationalize the different NLO anisotropies observed in the two isomer series through a detailed analysis of the symmetry of the low-lying excited states.

V-Shaped Tröger Oligothiophenes Boost Triplet Formation by CT Mediation and Symmetry Breaking.

A new family of molecules obtained by coupling Tröger's base unit with dicyanovinylene-terminated oligothiophenes of different lengths has been synthesized and characterized by steady-state stationary and transient time-resolved spectroscopies. Quantum chemical calculations allow us to interpret and recognize the properties of the stationary excited states as well as the time-dependent mechanisms of singlet-to-triplet coupling. The presence of the diazocine unit in Tröger's base derivatives is key to efficiently producing singlet-to-triplet intersystem crossing mediated by the role of the nitrogen atoms and of the almost orthogonal disposition of the two thiophene arms. Spin-orbit coupling-mediated interstate intersystem crossing (ISC) is activated by a symmetry-breaking process in the first singlet excited state with partial charge transfer character. This mechanism is a characteristic of these molecular triads since the independent dicyanovinylene-oligothiophene branches do not display appreciable ISC. These results show how Tröger's base coupling of organic chromophores can be used to improve the ISC efficiency and tune their photophysics.

Emergence of π-Magnetism in Fused Aza-Triangulenes: Symmetry and Charge Transfer Effects.

On-surface synthesis has paved the way toward the fabrication and characterization of conjugated carbon-based molecular materials that exhibit π-magnetism such as triangulenes. Aza-triangulene, a nitrogen-substituted derivative, was recently shown to display rich on-surface chemistry, offering an ideal platform to investigate structure-property relations regarding spin-selective charge transfer and magnetic fingerprints. Herein, we study electronic changes upon fusion of single molecules into larger dimeric derivatives. We show that the closed-shell structure of aza-triangulene on Ag(111) leads to closed-shell dimers covalently coupled through sterically accessible carbon atoms. Meanwhile, its open-shell structure on Au(111) leads to coupling via atoms displaying a high spin density, resulting in symmetric or asymmetric products. Interestingly, whereas all dimers on Au(111) exhibit similar charge transfer properties, only asymmetric ones show magnetic fingerprints due to spin-selective charge transfer. These results expose clear relationships among molecular symmetry, charge transfer, and spin states of π-conjugated carbon-based nanostructures.

Efficient Modeling of Quantum Dynamics of Charge Carriers in Materials Using Short Nonequilibrium Molecular Dynamics.

Nonadiabatic molecular dynamics provides essential insights into excited-state processes, but it is computationally intense and simplifications are needed. The classical path approximation provides critical savings. Still, long heating and equilibration steps are required. We demonstrate that practical results can be obtained with short, partially equilibrated ab initio trajectories. Once the system's structure is adequate and essential fluctuations are sampled, the nonadiabatic Hamiltonian can be constructed. Local structures require only 1-2 ps trajectories, as demonstrated with point defects in metal halide perovskites. Short trajectories represent anharmonic motions common in defective structures, an essential improvement over the harmonic approximation around the optimized geometry. Glassy systems, such as grain boundaries, require different simulation protocols, e.g., involving machine learning force fields. 10-fold shorter trajectories generate 10-20% time scale errors, which are acceptable, given experimental uncertainties and other approximations. The practical NAMD protocol enables fast screening of excited-state dynamics for rapid exploration of new materials.

State-Interaction Approach for Evaluating g-Tensors within EOM-CC and RAS-CI Frameworks: Theory and Benchmarks.

Among various techniques designed for studying open-shell species, electron paramagnetic resonance (EPR) spectroscopy plays an important role. The key quantity measured by EPR is the g-tensor, describing the coupling between an external magnetic field and molecular electronic spin. One theoretical framework for quantum chemistry calculations of g-tensors is based on response theory, which involves substantial developments that are specific to the underlying electronic structure models. A simplified and easier-to-implement approach is based on the state-interaction scheme, in which perturbation is included by considering a small number of states. We describe and benchmark the state-interaction approach using equation-of-motion coupled-cluster and restricted-active-space configuration interaction wave functions. The analysis confirms that this approach can deliver accurate results and highlights caveats of applying it, such as a choice of the reference state, convergence with respect to the number of states used in calculations, etc. The analysis also contributes toward a better understanding of challenges in calculations of higher-order properties using approximate wave functions.

Reversible spin-optical interface in luminescent organic radicals.

Molecules present a versatile platform for quantum information science1,2 and are candidates for sensing and computation applications3,4. Robust spin-optical interfaces are key to harnessing the quantum resources of materials5. To date, carbon-based candidates have been non-luminescent6,7, which prevents optical readout via emission. Here we report organic molecules showing both efficient luminescence and near-unity generation yield of excited states with spin multiplicity S > 1. This was achieved by designing an energy resonance between emissive doublet and triplet levels, here on covalently coupled tris(2,4,6-trichlorophenyl) methyl-carbazole radicals and anthracene. We observed that the doublet photoexcitation delocalized onto the linked acene within a few picoseconds and subsequently evolved to a pure high-spin state (quartet for monoradical, quintet for biradical) of mixed radical-triplet character near 1.8 eV. These high-spin states are coherently addressable with microwaves even at 295 K, with optical readout enabled by reverse intersystem crossing to emissive states. Furthermore, for the biradical, on return to the ground state the previously uncorrelated radical spins either side of the anthracene shows strong spin correlation. Our approach simultaneously supports a high efficiency of initialization, spin manipulations and light-based readout at room temperature. The integration of luminescence and high-spin states creates an organic materials platform for emerging quantum technologies.

On-Surface Synthesis and Characterization of a High-Spin Aza-[5]-Triangulene.

Triangulenes are a class of open-shell triangular graphene flakes with total spin increasing with their size. In the last years, on-surface-synthesis strategies have permitted fabricating and engineering triangulenes of various sizes and structures with atomic precision. However, direct proof of the increasing total spin with their size remains elusive. In this work, we report the combined in-solution and on-surface synthesis of a large nitrogen-doped triangulene (aza-[5]-triangulene) on a Au(111) surface, and the detection of its high-spin ground state. Bond-resolved scanning tunneling microscopy images uncovered radical states distributed along the zigzag edges, which were detected as weak zero-bias resonances in scanning tunneling spectra. These spectral features reveal the partial Kondo screening of a high-spin state. Through a combination of several simulation tools, we find that the observed distribution of radical states is explained by a quintet ground state (S=2), instead of the quartet state (S=3/2) expected for the neutral species. This confirms that electron transfer to the metal substrate raises the spin of the ground state. We further provide a qualitative description of the change of (anti)aromaticity introduced by N-substitution, and its role in the charge stabilization on a surface, resulting in an S=2 aza-triangulene on Au(111).

A Single-Crystal Monomer to Single-Crystal Polymer Reaction Activated by a Triplet Excimer in a Zipper Mechanism.

A combined experimental and theoretical study focused on the elucidation of the polymerization mechanism of the crystal monomer to crystal polymer reaction of a bisindenedione compound in the solid state. The experimental description and characterization of the polymer product have been reported elsewhere and, in this article, we address the first detailed description of the polymerization process. This reaction pathway consists of the initial formation of a triplet excimer state that relaxes to an intermolecularly bonded triplet state that is the starting point of the propagation step of the polymerization. The overall process can be visualized in the monomer starting state as an open zipper in which a cursor or slider is formed by light absorption and the whole zipper is then closed by propagation of the cursor. To this end, variable-temperature electron spin resonance (ESR), femtosecond transient absorption spectroscopy, and vibrational Raman spectroscopic data have been implemented in combination with quantum chemical calculations. The presented mechanistic insight is of great value to understand the intricacies of such an important reaction and to envisage and diversify the products produced thereof.