Elucidating Singlet-Fission-Born Multiexciton Dynamics via Molecular Engineering: A Dilution Principle Extended to Quintet Triplet Pair.

Multiexciton in singlet exciton fission represents a critical quantum state with significant implications for both solar cell applications and quantum information science. Two distinct fields of interest explore contrasting phenomena associated with the geminate triplet pair: one focusing on the persistence of long-lived correlation and the other emphasizing efficient decorrelation. Despite the pivotal nature of multiexciton processes, a comprehensive understanding of their dependence on the structural and spin properties of materials is currently lacking in experimental realizations. To address this gap in knowledge, molecular engineering was employed to modify the TIPS-tetracene structures, enabling an investigation of the structure-property relationships in spin-related multiexciton processes. In lieu of the time-resolved electron paramagnetic resonance technique, two time-resolved magneto-optical spectroscopies were implemented for quantitative analysis of spin-dependent multiexciton dynamics. The utilization of absorption and fluorescence signals as complementary optical readouts, in the presence of a magnetic field, provided crucial insights into geminate triplet pair dynamics. These insights encompassed the duration of multiexciton correlation and the involvement of the spin state in multiexciton decorrelation. Furthermore, simulations based on our kinetic models suggested a role for quintet dilution in multiexciton dynamics, surpassing the singlet dilution principle established by the Merrifield model. The integration of intricate model structures and time-resolved magneto-optical spectroscopies served to explicitly elucidate the interplay between structural and spin properties in multiexciton processes. This comprehensive approach not only contributes to the fundamental understanding of these processes but also aligns with and reinforces previous experimental studies of solid states and theoretical assessments.

Controlling Intramolecular Singlet Fission Dynamics via Torsional Modulation of Through-Bond versus Through-Space Couplings.

Covalent dimers, particularly pentacenes, are the dominant platform for developing a mechanistic understanding of intramolecular singlet fission (iSF). Numerous studies have demonstrated that a photoexcited singlet state in these structures can rapidly and efficiently undergo exciton multiplication to form a correlated pair of triplets within a single molecule, with potential applications from photovoltaics to quantum information science. One of the most significant barriers limiting such dimers is the fast recombination of the triplet pair, which prevents spatial separation and the formation of long-lived triplet states. There is an ever-growing need to develop general synthetic strategies to control the evolution of triplets following iSF and enhance their lifetime. Here, we rationally tune the dihedral angle and interchromophore separation between pairs of pentacenes in a systematic series of bridging units to facilitate triplet separation. Through a combination of transient optical and spin-resonance techniques, we demonstrate that torsion within the linker provides a simple synthetic handle to tune the fine balance between through-bond and through-space interchromophore couplings that steer iSF. We show that the full iSF pathway from femtosecond to microsecond timescales is tuned through the static coupling set by molecular design and structural fluctuations that can be biased through steric control. Our approach highlights a straightforward design principle to generate paramagnetic spin pair states with higher yields.

Neural Network Models for Driving Control of Indoor Autonomous Vehicles in Mobile Edge Computing.

Mobile edge computing has been proposed as a solution for solving the latency problem of traditional cloud computing. In particular, mobile edge computing is needed in areas such as autonomous driving, which requires large amounts of data to be processed without latency for safety. Indoor autonomous driving is attracting attention as one of the mobile edge computing services. Furthermore, it relies on its sensors for location recognition because indoor autonomous driving cannot use a GPS device, as is the case with outdoor driving. However, while the autonomous vehicle is being driven, the real-time processing of external events and the correction of errors are required for safety. Furthermore, an efficient autonomous driving system is required because it is a mobile environment with resource constraints. This study proposes neural network models as a machine-learning method for autonomous driving in an indoor environment. The neural network model predicts the most appropriate driving command for the current location based on the range data measured with the LiDAR sensor. We designed six neural network models to be evaluated according to the number of input data points. In addition, we made an autonomous vehicle based on the Raspberry Pi for driving and learning and an indoor circular driving track for collecting data and performance evaluation. Finally, we evaluated six neural network models in terms of confusion matrix, response time, battery consumption, and driving command accuracy. In addition, when neural network learning was applied, the effect of the number of inputs was confirmed in the usage of resources. The result will influence the choice of an appropriate neural network model for an indoor autonomous vehicle.

Superatom-in-Superatom Nanoclusters: Synthesis, Structure, and Photoluminescence.

We report a new strategy in which a thiolate-protected Ag25 nanocluster can be doped with open d-shell group 8 (Ru, Os) and 9 (Ir) metals by forming metal hydride (RuH2 , OsH2 , IrH) superatoms with a closed d-shell. Structural analyses using various experimental and theoretical methods revealed that the Ag25 nanoclusters were co-doped with the open d-shell metal and hydride species to produce superatom-in-superatom nanoclusters, establishing a novel superatom doping phenomenon for open d-shell metals. The synthesized superatom-in-superatom nanoclusters exhibited dopant-dependent photoluminescence (PL) properties. Comparative PL lifetime studies of the Ag25 nanoclusters doped with 8-10 group metals revealed that both radiative and nonradiative processes were significantly dependent on the dopant. The former is strongly correlated with the electron affinity of the metal dopant, whereas the latter is governed predominantly by the kernel structure changed upon the doping of the metal hydride(s).

Ultrafast Symmetry-Breaking Charge Separation in a Perylene Bisimide Dimer Enabled by Vibronic Coupling and Breakdown of Adiabaticity.

Perylene bisimides (PBIs) have received great attention in their applicability to optoelectronics. Especially, symmetry-breaking charge separation (SB-CS) in PBIs has been investigated to mimic the efficient light capturing and charge generation in natural light-harvesting systems. However, unlike ultrafast CS dynamics in donor-acceptor heterojunction materials, ultrafast SB-CS in a stacked homodimer has still been challenging due to excimer formation in the absence of rigidifying surroundings such as a special pair in the natural systems. Herein, we present the detailed mechanism of ultrafast photoinduced SB-CS occurring in a 1,7-bis(N-pyrrolidinyl) PBI dimer within a cyclophane. Through narrow-band and broad-band transient absorption spectroscopy, we demonstrate that ultrafast SB-CS in the dimer is enabled by the combination of (1) vibrationally coherent charge-transfer resonance-enhanced excimer formation and (2) breakdown of adiabaticity (formation of SB-CS diabats) in the excimer state via structural and solvent fluctuation. Quantum chemical calculations also underpin that the participation of strong electron-donating substituents in overall vibrational modes plays a crucial role in triggering the ultrafast SB-CS. Therefore, our work provides an alternative route to facilitate ultrafast SB-CS in PBIs and thereby establishes a novel strategy for the design of optoelectronic materials.

Real-time Observation of Structural Dynamics Triggering Excimer Formation in a Perylene Bisimide Folda-dimer by Ultrafast Time-Domain Raman Spectroscopy.

In π-conjugated organic photovoltaic materials, an excimer state has been generally regarded as a trap state which hinders efficient excitation energy transport. But despite wide investigations of the excimer for overcoming the undesirable energy loss, the understanding of the relationship between the structure of the excimer in stacked organic compounds and its properties remains elusive. Here, we present the landscape of structural dynamics from the excimer formation to its relaxation in a co-facially stacked archetypical perylene bisimide folda-dimer using ultrafast time-domain Raman spectroscopy. We directly captured vibrational snapshots illustrating the ultrafast structural evolution triggering the excimer formation along the interchromophore coordinate on the complex excited-state potential surfaces and following evolution into a relaxed excimer state. Not only does this work showcase the ultrafast structural dynamics necessary for the excimer formation and control of excimer characteristics but also provides important criteria for designing the π-conjugated organic molecules.

Navigating Stigma Trajectory and Mental Health Among Young Adults Living with Perinatal HIV in New York City.

Perceived HIV stigma and mental health are fluid across the lifespan for people living with perinatally-acquired HIV (PHIV). The process of navigating discredited identities over time in the context of other life demands potentially exerts a toll on the mental health of adolescents and young adults living with PHIV (AYAPHIV). Based on data from a longitudinal study in New York City examining mental health and health risk behaviors among 182 AYAPHIV, we examined if increased perceived HIV stigma predicted mental health, future orientation, HIV-disclosure, and healthcare transition over time (2003-2018). Findings from linear mixed-effects modeling indicated that older age predicted poorer mental health, less future orientation, more HIV-serostatus disclosure, and adult medical services utilization. Perceived stigma was the only significant predictor of mental health and mediated the association between age and mental health-highlighting the importance of addressing stigma across development for AYAPHIV while addressing systems that perpetuate them.

Simulator for Interactive and Effective Organization of Things in Edge Cluster Computing.

Edge computing is intended to process events that occur at the endpoint of the Internet of Things (IoT) network quickly and intelligently. Edge regions must be organized effectively to facilitate cooperation so that the intention of edge computing can be realized. However, inevitably, many human and material resources are required in the process of arranging things in the edge area to confirm the appropriateness of the thing operation. To address this problem, we proposed a simulator that created a virtual space for edge computing and provided an interactive role and effective organization for edge things. The proposed simulator was aimed at Raspberry Pi as the physical hardware target. To prove the accuracy of the proposed simulator, the similarity between the proposed simulator and the physical target Raspberry Pi was evaluated based on three metrics while executing several applications. In the experiment, several edge-computing service applications were performed in various cluster architecture types formed by the proposed simulator. To support effective resource usage and fast real-time response for edge computing, the proposed simulator identified a suitable number of things in forming the edge cluster.

Biomechanical properties of canine staphylectomies closed with barbed or smooth suture.

OBJECTIVE: To compare the duration of closure and biomechanical properties of staphylectomies closed with absorbable bidirectional barbed suture or smooth monofilament suture in a simple continuous or interrupted pattern STUDY DESIGN: Ex vivo study SAMPLE POPULATION: Soft palates (n = 60) harvested from mesaticephalic canine cadavers METHODS: One centimeter of tissue was excised from the caudal border of each soft palate, and the oral and nasopharyngeal mucosal surfaces were apposed with 2-0 bidirectional Quill Monoderm knotless closure device barbed suture (Q), 3-0 Monocryl in a simple continuous (MC) pattern, or 3-0 Monocryl in a simple interrupted (MI) pattern (n = 20 per group). Duration of closure was compared between groups. Tissues were tested under tension to failure, and mode of failure data were collected by video capture. RESULTS: Closure time was longer for MI closures than for Q and MC closures, with means of 259.9, 215.4, and 196.7 seconds, respectively (P < .0001). No difference was detected in yield force, force to first tissue rupture, maximum force, and energy required for yield and maximum force between groups. Energy to yield was 190.0, 167.8, and 188.95 N-mm for MI, Q, and MC closures, respectively. CONCLUSION: Biomechanical properties of staphylectomies closed with barbed or smooth sutures did not differ in this cadaveric model. CLINICAL SIGNIFICANCE: Barbed suture can be considered as an alternative for closure of canine staphylectomies. These results provide evidence to justify additional research to evaluate clinical outcomes in dogs undergoing staphylectomy.

Gray Ramus Communicans Nerve Block for Acute Pain Control in Vertebral Compression Fracture.

Background and Objectives: The current options for acute pain control of vertebral compression fracture include hard brace, vertebroplasty, early surgery, and analgesic injection. We hypothesize that the gray ramus communicans nerve block (GRNB) controls the acute pain experienced during vertebral compression fractures. This study assessed the time course of pain control after injection and evaluated the risk factors affecting pain control failure. Materials and methods: Sixty-three patients (24 male, 66.19 ± 15.17 y) with a thoracolumbar vertebral fracture at the T10-L5 spine, who presented to our hospital from November 2018 to October 2019, were included in this retrospective cohort study. GRNB was performed within 1 week of the trauma. The patients were followed up on days 3, 14, 30, 90, and 180 and assessed with the serial visual analog scale (VAS, resting and motion), Oswestry Low Back Disability (ODI) questionnaire, and Roland-Morris Disability Questionnaire (RDQ). The failure group was defined by the need for an additional block or cement injection after a single GRNB. The failure group's risk factors, such as body mass index, initial thoracolumbar injury classification and severity score, Kummel's disease, age, bone marrow density (BMD), and underlying disease, were analyzed. Results: The motion VAS score improved from preoperative to three months post-procedure, but the resting VAS was affected by the procedure for only three days. The quality of life index improved at postoperative six months. A lower BMD was the only risk that affected treatment failure in the logistic regression analysis (p = 0.0038). Conclusion: The effect of GRNB was maintained even at three months after trauma based on motion VAS results. The only risk factor identified for GRNB failure was lower BMD.

Mode-Specific Vibrational Analysis of Exciton Delocalization and Structural Dynamics in Conjugated Oligomers.

Exciton delocalization in organic semiconducting polymers, affected by structures at a molecular level, plays a crucial role in modulating relaxation pathways, such as charge generation and singlet fission, which can boost device efficiency. However, the structural diversity of polymers and broad signals from typical electronic spectroscopy have their limits when it comes to revealing the interplay between local structures and exciton delocalization. To tackle these problems, we apply femtosecond stimulated Raman spectroscopy in archetypical conjugated oligothiophenes with different chain lengths. We observed Raman frequency dispersions of symmetric bond stretching modes and mode-specific kinetics in the S1 Raman spectra, which underpins the subtle and complex interplay between exciton delocalization and bond length alternation along the conjugation coordinate. Our results provide a more general picture of exciton delocalization in the context of molecular structures for conjugated materials.

Two-Step Charge Separation Passing Through the Partial Charge-Transfer State in a Molecular Dyad.

Charge separation (CS) in molecular systems usually takes place in weakly coupled donor-acceptor dyads where an electron charge moves from the donor to the acceptor in the local excited state of a chromophore. Herein, we present a two-step charge-separation process in a newly synthesized diketopyrrolopyrrole-pyrrolopyrrole (DPP-PP) dyad (AD), which starts from the initial photoexcited bright exciton and goes through a partial charge-transfer (CT) state before finally reaching the charge-separated (CS) state. The evolving CT character in the excited state is demonstrated through the complementary use of transient absorption, broad-band fluorescence upconversion, and transient impulsive stimulated Raman spectroscopy. The bright exciton state of the dyad relaxes to a partial CT state with 1 and 20 ps during solvent and structural fluctuations in toluene, respectively, and with 700 fs for the solvent fluctuations occurring in tetrahydrofuran. This is evident from the characteristic excited-state absorption spectra and the reduced fluorescence intensity observed on the adiabatic potential energy surface. AD in THF additionally evolves to the diabatic potential energy surface of the CS state, whose absorption spectrum converges to that of a DPP anion for which fluorescence is completely quenched. The trend of shifting for certain vibrational frequencies also supports the proposed CT dynamics and mechanism; furthermore, it gives quantitative insight into the CT characters of the bright state (0.1 e) and intermediate partial CT state (0.5 e), as determined by the linear relationship that exists between the vibrational frequency of the marker modes and the CT character. We have found that as the structure of the bridge between donor and acceptor enables an intermediate level of electronic communication, the charge-separation can rapidly occur through a distinct partial charge-transfer state. It seems that the exceptionally strong electronic communication at positions 2 and 5 of the pyrrolo[3,2-b]pyrrole core is a crucial element for this charge-transfer mechanism, which could be applied to organic photovoltaics or light-emitting diodes requiring efficient charge separation.

Efficient Multiexciton State Generation in Charge-Transfer-Coupled Perylene Bisimide Dimers via Structural Control.

The singlet fission (SF) process is generally defined as the conversion of one singlet exciton (S1) into two triplet excitons (2·T1), which has the potential to overcome thermalization losses in the field of photovoltaic devices. Among the applicable compounds for SF-based photovoltaic devices, perylene bisimide (PBI) is one of the best candidates because of its electronic tunability and photostability. However, the strategy for efficient SF in PBIs remains ambiguous because of numerous competing relaxation pathways in PBI-based molecular materials. In this regard, for the first time, we observed the SF mechanism in PBI dimers by controlling the intrinsic factor (exciton coupling) and the external environment (solvent polarity and viscosity). Time-resolved spectroscopic measurements and quantum chemical simulations reveal that efficient SF occurs through the charge-transfer-assisted mechanism, entailing a large structural fluctuation. Our findings not only highlight the SF mechanism in PBI dimers but also suggest the factors responsible for an efficient SF process, which are important considerations in the design of molecular materials for photovoltaic devices.

Tracking Structural Evolution during Symmetry-Breaking Charge Separation in Quadrupolar Perylene Bisimide with Time-Resolved Impulsive Stimulated Raman Spectroscopy.

Elucidating structural roles in photoinduced charge transfer is indispensable, as nuclear rearrangements are simultaneously usually involved in the dynamics. However, it is hard to evaluate whether the structural changes occur or not by using conventional time-resolved electronic spectroscopy. Here, time-resolved impulsive stimulated Raman spectroscopy is applied to record the evolution of vibrational snapshots during charge-separation dynamics of donor-acceptor-donor-type quadrupolar perylene bisimide in real time. Drastic frequency shifts were observed for several Raman bands with their population kinetics, thus symmetry-breaking charge separation accompanies significant structural changes, as supported by (TD)-DFT calculations. A comparison between time-resolved Raman spectra of the neutral S1 state and the radical anion species shows that the spectral signatures, especially in high-frequency regions, provide important clues to bond length alternation patterns in the PBI core.

Ultrafast Exciton Self-Trapping and Delocalization in Cycloparaphenylenes: The Role of Excited-State Symmetry in Electron-Vibrational Coupling.

Upon photon absorption, π-conjugated organics are apt to undergo ultrafast structural reorganization via electron-vibrational coupling during non-adiabatic transitions. Ultrafast nuclear motions modulate local planarity and quinoid/benzenoid characters within conjugated backbones, which control primary events in the excited states, such as localization, energy transfer, and so on. Femtosecond broadband fluorescence upconversion measurements were conducted to investigate exciton self-trapping and delocalization in cycloparaphenylenes as ultrafast structural reorganizations are achieved via excited-state symmetry-dependent electron-vibrational coupling. By accessing two high-lying excited states, one-photon and two-photon allowed states, a clear discrepancy in the initial time-resolved fluorescence spectra and the temporal dynamics/spectral evolution of fluorescence spectra were monitored. Combined with quantum chemical calculations, a novel insight into the effect of the excited-state symmetry on ultrafast structural reorganization and exciton self-trapping in the emerging class of π-conjugated materials is provided.

Control and Switching of Aromaticity in Various All-Aza-Expanded Porphyrins: Spectroscopic and Theoretical Analyses.

Modification of aromaticity is regarded as one of the most interesting and important research topics in the field of physical organic chemistry. Particularly, porphyrins and their analogues (porphyrinoids) are attractive molecules for exploring various types of aromaticity because most porphyrinoids exhibit circular conjugation pathways in their macrocyclic rings with various molecular structures. Aromaticity in porphyrinoids is significantly affected by structural modification, redox chemistry, NH tautomerization, and electronic states (singlet and triplet excited states). Conversely, aromaticity significantly affects the spectroscopic properties and chemical reactivities of porphyrinoids. In this context, considerable efforts have been devoted to understanding and controlling the aromaticity and antiaromaticity of porphyrinoids. Thus, a series of porphyrinoids are in the limelight, being expected to shed light on this field because they have some advantages to demonstrate the switching of aromaticity; it is possible to control the aromaticity by lowering the temperature, adding and removing the protons of expanded porphyrins, changing the chemical environment, and switching the electronic states (triplet and singlet excited states) by photoexcitation. In this regard, this Review describes the control of aromaticity in various expanded porphyrins from the spectroscopic point of view with assistance from theoretical calculations.

Enhanced thermal stability of InP quantum dots coated with Al-doped ZnS shell.

Colloidal InP quantum dots (QDs) have attracted a surge of interest as environmentally friendly light-emitters in downconversion liquid crystal displays and light-emitting diodes (LEDs). A ZnS shell on InP-based core QDs has helped achieve high photoluminescence (PL) quantum yield (QY) and stability. Yet, due to the difficulty in the growth of a thick ZnS shell without crystalline defects, InP-based core/shell QDs show inferior stability against QY drop compared to Cd chalcogenide precedents, e.g., CdSe/CdS core/thick-shell QDs. In this work, we demonstrate the synthesis of InP-based core/shell QDs coated with an Al-doped ZnS outer shell. QDs with an Al-doped shell exhibit remarkable improvement in thermal and air stability even when the shell thickness is below 2 nm, while the absorption and PL spectra, size, and crystal structure are nearly the same as the case of QDs with a pristine ZnS shell. X-ray photoelectron spectroscopy reveals that Al3+ in Al-doped QDs forms an Al-oxide layer at elevated temperature under ambient atmosphere. The as-formed Al-oxide layer blocks the access of external oxidative species penetrating into QDs and prevents QDs from oxidative degradation. We also trace the chemical pathway of the incorporation of Al3+ into ZnS lattice during the shell growth. Furthermore, we fabricate QD-LEDs using Al-doped and undoped QDs and compare the optoelectronic characteristics and stability.

Excited-state structural relaxation and exciton delocalization dynamics in linear and cyclic π-conjugated oligothiophenes.

π-Conjugated oligothiophene is considered a chain segment of its polymeric counterpart, whose size and shape can be precisely controlled. Because of its simplified structure, it is possible to understand complex excited-state dynamics of the π-conjugated polymers by employing a bottom-up approach. We review theoretical and experimental aspects of π-conjugated oligothiophenes by summarizing recent works employing time-resolved spectroscopy. The extent of exciton delocalization, which is a prerequisite to efficient charge generation at organic heterojunctions, is described sequentially in model linear and cyclic oligothiophenes, and their analogues. The heterogeneous nature of these systems is highlighted by illustrating the results at both ensemble and single-molecule levels. Exciton dynamics that arise in the polymers are also covered and the signifcance of exciton and charge delocalization in photovoltaic materials is highlighted.

Smart Sensing Period for Efficient Energy Consumption in IoT Network.

The devices included in IoT networks have sensors and actuators for monitoring their surroundings. These operate on battery energy, according to the characteristics of the environment in which they are deployed. To enhance the longevity of IoT networks, the devices need to avoid any unnecessary sensing operations in order to reduce the power consumption rate. However, as existing sensing methods use a fixed sensing period policy, battery power wastage is inevitable. In this paper, a smart sensing period policy is proposed for efficient energy consumption in an IoT network. The proposed method uses a learning model based on a back-propagation neural network. Within the target time, it can efficiently use the battery energy without any surplus or wastage in the quantity of preserved battery energy. In experiments, our proposed method shows improved results in battery energy consumption rates compared to the existing sensing period methods.

Biomechanical comparison of three epitendinous suture patterns as adjuncts to a core locking loop suture for repair of canine flexor tendon injuries.

OBJECTIVE: To determine the effects of different epitendinous sutures (ES) in addition to core locking-loop (LL) sutures on the mechanical properties and gap formation in a canine cadaveric tendon model. STUDY DESIGN: Experimental, ex vivo, biomechanical study. SAMPLE POPULATION: Seventy-two cadaveric superficial digital flexor tendon specimens. METHODS: Superficial digital flexor tendon specimens were divided into four groups (n = 18): sharply transected and repaired with LL, LL + simple continuous ES, LL + Silfverskiöld cross-stitch ES, and LL + interlocking horizontal mattress ES. Constructs were loaded to monotonic failure. Failure modes, gapping, yield, peak, and failure forces were analyzed. Significance was set at P < .05. RESULTS: Yield, peak, and failure forces increased by 2.5-fold, two-fold, and twofold, respectively when ES groups were compared with core LL suture patterns alone (P < .0001). Resistance to 1- and 3-mm gap formation was greater in ES groups compared with core LL constructs alone (P < .0001). No differences in yield, peak, failure force, or gapping were observed among ES patterns (P > .827). CONCLUSION: Adding an ES reduced gap formation and increased yield, peak, and failure forces of tenorrhaphies. No difference was detected between the epitendinous patterns tested in this study. CLINICAL SIGNIFICANCE: The addition of an ES seems more relevant than the specific type of pattern to improve the biomechanical properties of flexor tendon repairs. In vivo studies are warranted to determine the biological implications of the patterns tested here.