Large Reorganization Research Articles

EcDBS1R4, an Antimicrobial Peptide Effective against Escherichia coli with In Vitro Fusogenic Ability.

Discovering antibiotic molecules able to hold the growing spread of antimicrobial resistance is one of the most urgent endeavors that public health must tackle. The case of Gram-negative bacterial pathogens is of special concern, as they are intrinsically resistant to many antibiotics, due to an outer membrane that constitutes an effective permeability barrier. Antimicrobial peptides (AMPs) have been pointed out as potential alternatives to conventional antibiotics, as their main mechanism of action is membrane disruption, arguably less prone to elicit resistance in pathogens. Here, we investigate the in vitro activity and selectivity of EcDBS1R4, a bioinspired AMP. To this purpose, we have used bacterial cells and model membrane systems mimicking both the inner and the outer membranes of Escherichia coli, and a variety of optical spectroscopic methodologies. EcDBS1R4 is effective against the Gram-negative E. coli, ineffective against the Gram-positive Staphylococcus aureus and noncytotoxic for human cells. EcDBS1R4 does not form stable pores in E. coli, as the peptide does not dissipate its membrane potential, suggesting an unusual mechanism of action. Interestingly, EcDBS1R4 promotes a hemi-fusion of vesicles mimicking the inner membrane of E. coli. This fusogenic ability of EcDBS1R4 requires the presence of phospholipids with a negative curvature and a negative charge. This finding suggests that EcDBS1R4 promotes a large lipid spatial reorganization able to reshape membrane curvature, with interesting biological implications herein discussed.

Asymmetrically 2,7-difunctionalized carbazole-based donor-acceptor hybrids for deep blue electroluminescence applications

Asymmetrically 2,7-difunctionalized carbazoles decorated with cyano group and different conjugated chromophores have been synthesized by following Suzuki coupling reactions. Direct C–C coupling between cyanocarbazole and peripheral chromophores lead to twist structure of the molecules. As a result, it restricts the electronic communication between the chromophores and thereby confines absorption and emission maxima in shorter wavelength region. The positive solvatochromic emission spectrum of carbazole and triphenylamine substituted compounds is ascribed to synergistic effect of large structural reorganization and intramolecular charge transfer at excited state. Density functional theory (DFT) studies reveal the involvement of ICT from donor carbazole/triphenylamine to cyanocarbazole acceptor. OLED device containing a pyrene substituted dye (5 wt% in CBP host) displayed deep blue electroluminescence with the EQE of 3.0% and CIE of (0.16, 0.06). The superior device performance can be attributed to favorable energy level alignment of this dye with CBP host and complete energy transfer from the host to guest.

Excitation quenching in chlorophyll\u2013carotenoid antenna systems: \u2018coherent\u2019 or \u2018incoherent\u2019

Plants possess an essential ability to rapidly down-regulate light-harvesting in response to high light. This photoprotective process involves the formation of energy-quenching interactions between the chlorophyll and carotenoid pigments within the antenna of Photosystem II (PSII). The nature of these interactions is currently debated, with, among others, ‘incoherent’ or ‘coherent’ quenching models (or a combination of the two) suggested by a range of time-resolved spectroscopic measurements. In ‘incoherent quenching’, energy is transferred from a chlorophyll to a carotenoid and is dissipated due to the intrinsically short excitation lifetime of the latter. ‘Coherent quenching’ would arise from the quantum mechanical mixing of chlorophyll and carotenoid excited state properties, leading to a reduction in chlorophyll excitation lifetime. The key parameters are the energy gap, Updelta varepsilon =varepsilon_{rm Car}-varepsilon_{rm Chl}, and the resonance coupling, J, between the two excited states. Coherent quenching will be the dominant process when -J<Updelta varepsilon <J, i.e., when the two molecules are resonant, while the quenching will be largely incoherent when varepsilon_{rm Chl}>(varepsilon_{rm Car}+J). One would expect quenching to be energetically unfavorable for varepsilon_{rm Chl}<(varepsilon_{rm Car}-J). The actual dynamics of quenching lie somewhere between these limiting regimes and have non-trivial dependencies of both J and Updelta varepsilon. Using the Hierarchical Equation of Motion (HEOM) formalism we present a detailed theoretical examination of these excitation dynamics and their dependence on slow variations in J and Updelta varepsilon. We first consider an isolated chlorophyll–carotenoid dimer before embedding it within a PSII antenna sub-unit (LHCII). We show that neither energy transfer, nor the mixing of excited state lifetimes represent unique or necessary pathways for quenching and in fact discussing them as distinct quenching mechanisms is misleading. However, we do show that quenching cannot be switched ‘on’ and ‘off’ by fine tuning of Updelta varepsilon around the resonance point, Updelta varepsilon =0. Due to the large reorganization energy of the carotenoid excited state, we find that the presence (or absence) of coherent interactions have almost no impact of the dynamics of quenching. Counter-intuitively significant quenching is present even when the carotenoid excited state lies above that of the chlorophyll. We also show that, above a rather small threshold value of J>10,mathrm{cm}^{-1}quenching becomes less and less sensitive to J (since in the window -J<Updelta varepsilon <J the overall lifetime is independent of it). The requirement for quenching appear to be only that J>0. Although the coherent/incoherent character of the quenching can vary, the overall kinetics are likely robust with respect to fluctuations in J and Updelta varepsilon. This may be the basis for previous observations of NPQ with both coherent and incoherent features.

Stimulating Peer Effects? Evidence from a Research Cluster Policy

Production of knowledge relies on peer effects and interactions between researchers. However, little is known on how much policies may stimulate these peer effects. In this paper we shed light on this question, and show how a public cluster'' policy, which funds local networks of researchers working on a common theme, affects the organization of research within these clusters and the productivity of its members. Using data from a large scale financing program in France, and relying on an identification strategy based on grades awarded by reviewers, we show that members of financed clusters increase by up to 30% the research collaborations they have with other members of the cluster, compared to researchers of non selected proposals. This very large reorganization of the research network translates into a more modest positive effect on research productivity. Paradoxically, those who benefit the most from the financing, are those who were not at the core of the research topic, i.e. were not cited in the bibliography of the research proposal, who significantly increase their links with core members and their total publication counts. Consistently, the policy reduces inequality in publication outcomes within the cluster. It stimulates peer effects to the benefit of periphery members.

An Exceptionally Stable and Scalable Sugar–Polyolefin Frank–Kasper A15 Phase

Abstract“One‐component” soft material Frank–Kasper (FK) phases are an intriguing structural form of matter that possess periodically ordered structures arising from the self‐reconfiguration and close packing of an initial assembly of identical “deformable” spheres into two or more size‐ or shape‐distinct sets of particles. Significant challenges that must still be addressed to advance the field of soft matter FK phases further, however, include their rare and unpredictable occurrence, uncertain mechanisms of solid‐state assembly, and low thermodynamic stability. Here we show that a readily‐accessible sugar–polyolefin conjugate quantitatively produces an exceptionally stable solid‐state FK A15 phase through a rapid and irreversible thermotropic order–order transition, which contrary to other prevailing proposed mechanisms, does not require mass transfer between particles or large structural reorganization in the bulk to establish unit cell non‐equivalency. Our results provide the basis for a realistic strategy for obtaining practical and scalable quantities of a diverse range of sugar–polyolefin FK A15 phases with unique intrinsic physical properties and chemical reactivities not previously seen in such systems.

An Exceptionally Stable and Scalable Sugar-Polyolefin Frank-Kasper A15 Phase.

"One-component" soft material Frank-Kasper (FK) phases are an intriguing structural form of matter that possess periodically ordered structures arising from the self-reconfiguration and close packing of an initial assembly of identical "deformable" spheres into two or more size- or shape-distinct sets of particles. Significant challenges that must still be addressed to advance the field of soft matter FK phases further, however, include their rare and unpredictable occurrence, uncertain mechanisms of solid-state assembly, and low thermodynamic stability. Here we show that a readily-accessible sugar-polyolefin conjugate quantitatively produces an exceptionally stable solid-state FK A15 phase through a rapid and irreversible thermotropic order-order transition, which contrary to other prevailing proposed mechanisms, does not require mass transfer between particles or large structural reorganization in the bulk to establish unit cell non-equivalency. Our results provide the basis for a realistic strategy for obtaining practical and scalable quantities of a diverse range of sugar-polyolefin FK A15 phases with unique intrinsic physical properties and chemical reactivities not previously seen in such systems.

Peripheral Nerve Ligation Elicits Widespread Alterations in Cortical Sensory Evoked and Spontaneous Activity

Peripheral neuropathies result in adaptation in primary sensory and other regions of cortex, and provide a framework for understanding the localized and widespread adaptations that arise from altered sensation. Mesoscale cortical imaging achieves high temporal resolution of activity using optical sensors of neuronal activity to simultaneously image across a wide expanse of cortex and capture this adaptation using sensory-evoked and spontaneous cortical activity. Saphenous nerve ligation in mouse is an animal model of peripheral neuropathy that produces hyperalgesia circumscribed to the hindlimb. We performed saphenous nerve ligation or sham, followed by mesoscale cortical imaging using voltage sensitive dye (VSD) after ten days. We utilized subcutaneous electrical stimulation at multiple stimulus intensities to characterize sensory responses after ligation or sham, and acquired spontaneous activity to characterize functional connectivity and large scale cortical network reorganization. Relative to sham animals, the primary sensory-evoked response to hindlimb stimulation in ligated animals was unaffected in magnitude at all stimulus intensities. However, we observed a diminished propagating wave of cortical activity at lower stimulus intensities in ligated animals after hindlimb, but not forelimb, sensory stimulation. We simultaneously observed a widespread decrease in cortical functional connectivity, where midline association regions appeared most affected. These results are consistent with localized and broad alterations in intracortical connections in response to a peripheral insult, with implications for novel circuit level understanding and intervention for peripheral neuropathies and other conditions affecting sensation.

Objective and Subjective Effects of a Passive Exoskeleton on Overhead Work.

Overhead work is a frequent cause of shoulder work-related musculoskeletal disorders. Exoskeletons offering arm support have the potential to reduce shoulder strain, without requiring large scale reorganization of the workspace. Assessment of such systems however requires to take multiple factors into consideration. This paper presents a thorough in-lab assessment of PAEXO, a novel passive exoskeleton for arm support during overhead work. A list of evaluation criteria and associated performance metrics is proposed to cover both objective and subjective effects of the exoskeleton, on the user and on the task being performed. These metrics are measured during a lab study, where 12 participants perform an overhead pointing task with and without the exoskeleton, while their physical, physiological and psychological states are monitored. Results show that using PAEXO reduces shoulder physical strain as well as global physiological strain, without increasing low back strain nor degrading balance. These positive effects are achieved without degrading task performance. Importantly, participants' opinions of PAEXO are positive, in agreement with the objective measures. Thus, PAEXO seems a promising solution to help prevent shoulder injuries and diseases among overhead workers, without negatively impacting productivity.

Structural Origin of the Large Redox-Linked Reorganization in the 2-Oxoglutarate Dependent Oxygenase, TauD.

2-Oxoglutarate (2OG)-dependent oxygenases catalyze a wide range of chemical transformations via C-H bond activation. Prior studies raised the question of whether substrate hydroxylation by these enzymes occurs via a hydroxyl rebound or alkoxide mechanism and highlighted the need to understand the thermodynamic properties of transient intermediates. A recent spectroelectrochemical investigation of the 2OG-dependent oxygenase, taurine hydroxylase (TauD), revealed a strong link between the redox potential of the Fe(II)/Fe(III) couple and conformational changes of the enzyme. In this study, we show that the redox potential of wild-type TauD varies by 468 mV between the reduction of 2OG-Fe(III)-TauD (-272 mV) and oxidation of 2OG-Fe(II)-TauD (+196 mV). We use active site variants to investigate the structural origin of the redox-linked reorganization and the contributions of the metal-bound residues to the dynamic tuning of the redox potential of TauD. Time-dependent redox titrations show that reorganization occurs as a multistep process. Transient optical absorption and infrared spectroelectrochemistry show that substitution of any metal ligand alters the kinetics and thermodynamics of the reorganization. The H99A variant shows the largest net redox change relative to the wild-type protein, suggesting that redox-coupled protonation of H99 is required for high redox potentials of the metal. The D101Q and H255Q variants also suppress the conformational change, supporting their involvement in the structural rearrangement. Similar redox-linked conformational changes are observed in another 2OG dependent oxygenase, ethylene-forming enzyme, indicating that dynamic structural flexibility and the associated thermodynamic tuning may be a common phenomenon in this family of enzymes.

Neighboring base sequence effect on DNA damage

Guanine is the most strongly oxidized base in DNA; generation of a guanine radical cation as an intermediate in an oxidation reaction leads to migration through a resulting cationic hole in the DNA π-stack until it is trapped by irreversible reaction with water or other free radicals. In the case of normal sequences, the primary position of Guanine oxidations by one-electron oxidants such as carbonate radical anions, BPT(7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene), and riboflavin are 5′-G in GG doublets and the central G in a GGG triplet. According to results, the properties of guanine oxidation on abasic site containing sequences are independent from the position of AP(apurinic/apyrimidinic) site in the presence of carbonate radical anions under a short irradiation time, although this radical is exposed to solvent by the existence of an abasic site. The lack of abasic site effect on guanine oxidative damage by the carbonate radical may be due to a sequence-independent property of the initial electron transfer rate in the hole injection step, or may relate to an electron transfer mechanism with large reorganization energy dependency. Consequently, the carbonate radical anions may easily migrate to another single G in the charge re-distribution step. Meanwhile, there is a strong dependency on the presence of an AP(apurinic/apyrimidinic) site in the cleavage patterns of guanine oxidations by physically large oxidizing agents, such as BPT(7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene) and riboflavin. These radicals show strong AP(apurinic/apyrimidinic) site dependency and clear G-site selectivity.Communicated by Ramaswamy H. Sarma

Ergodicity-Breaking in Thermal Biological Electron Transfer? Cytochrome C Revisited.

It was recently suggested that certain redox proteins operate in an ergodicity-breaking regime to facilitate biological electron transfer (ET). A signature for this is a large variance reorganization free energy (several electronvolts) but a significantly smaller Stokes reorganization free energy due to incomplete protein relaxation on the time scale of the ET event. Here we investigate whether this picture holds for oxidation of cytochrome c in aqueous solution, at various levels of theory including classical molecular dynamics with two additive and one electronically polarizable force field, and QM/MM calculations with the QM region treated by full electrostatic DFT embedding and by the perturbed matrix method. Sampling the protein and energy gap dynamics over more than 250 ns, we find no evidence for ergodicity-breaking effects. In particular, the inclusion of electronic polarizability of the heme group at QM/MM levels did not induce nonergodic effects, contrary to previous reports by Matyushov et al. The well-known problem of overestimation of reorganization free energies with additive force fields is cured when the protein and solvent are treated as electronically polarizable. Ergodicity-breaking effects may occur in other redox proteins, and our results suggest that long simulations, ideally on the ET time scale, with electronically polarizable force fields are required to obtain strong numerical evidence for them.

Ligand Selectivity in the Recognition of Protoberberine Alkaloids by Hybrid-2 Human Telomeric G-Quadruplex: Binding Free Energy Calculation, Fluorescence Binding, and NMR Experiments.

The human telomeric G-quadruplex (G4) is an attractive target for developing anticancer drugs. Natural products protoberberine alkaloids are known to bind human telomeric G4 and inhibit telomerase. Among several structurally similar protoberberine alkaloids, epiberberine (EPI) shows the greatest specificity in recognizing the human telomeric G4 over duplex DNA and other G4s. Recently, NMR study revealed that EPI recognizes specifically the hybrid-2 form human telomeric G4 by inducing large rearrangements in the 5′-flanking segment and loop regions to form a highly extensive four-layered binding pocket. Using the NMR structure of the EPI-human telomeric G4 complex, here we perform molecular dynamics free energy calculations to elucidate the ligand selectivity in the recognition of protoberberines by the human telomeric G4. The MM-PB(GB)SA (molecular mechanics-Poisson Boltzmann/Generalized Born) Surface Area) binding free energies calculated using the Amber force fields bsc0 and OL15 correlate well with the NMR titration and binding affinity measurements, with both calculations correctly identifying the EPI as the strongest binder to the hybrid-2 telomeric G4 wtTel26. The results demonstrated that accounting for the conformational flexibility of the DNA-ligand complexes is crucially important for explaining the ligand selectivity of the human telomeric G4. While the MD-simulated (molecular dynamics) structures of the G-quadruplex-alkaloid complexes help rationalize why the EPI-G4 interactions are optimal compared with the other protoberberines, structural deviations from the NMR structure near the binding site are observed in the MD simulations. We have also performed binding free energy calculation using the more rigorous double decoupling method (DDM); however, the results correlate less well with the experimental trend, likely due to the difficulty of adequately sampling the very large conformational reorganization in the G4 induced by the protoberberine binding.

Energy windows for computed compound conformers: covering artefacts or truly large reorganization energies?

The generation of 3D conformers of small molecules underpins most computational drug discovery. Thus, the conformer quality is critical and depends on their energetics. A key parameter is the empirical conformational energy window (ΔEw), since only conformers within ΔEw are retained. However, ΔEw values in use appear unrealistically large. We analyze the factors pertaining to the conformer energetics and ΔEw. We argue that more attention must be focused on the problem of collapsed low-energy conformers. That is due to artificial intramolecular stabilization and occurs even with continuum solvation. Consequently, the conformational energy of extended bioactive structures is artefactually increased, which inflates ΔEw. Thus, this Perspective highlights the issues arising from low-energy conformers and suggests improvements via empirical or physics-based strategies.

Switching between Stepwise and Concerted Proton-Coupled Electron Transfer Pathways in Tungsten Hydride Activation.

Catalytic processes to generate (or oxidize) fuels such as hydrogen are underpinned by multiple proton-coupled electron transfer (PCET) steps that are associated with the formation or activation of metal-hydride bonds. Fully understanding the detailed PCET mechanisms of metal hydride transformations holds promise for the rational design of energy-efficient catalysis. Here we investigate the detailed PCET mechanisms for the activation of the transition metal hydride complex CpW(CO)2(PMe3)H (Cp = cyclopentadienyl) using stopped-flow rapid mixing coupled with time-resolved optical spectroscopy. We reveal that all three limiting PCET pathways can be accessed by changing the free energy for elementary proton, electron, and proton-electron transfers through the choice of base and oxidant, with the concerted pathway occurring exclusively as a secondary parallel route. Through detailed kinetics analysis, we define free energy relationships for the kinetics of elementary reaction steps, which provide insight into the factors influencing reaction mechanism. Rate constants for proton transfer processes in the limiting stepwise pathways reveal a large reorganization energy associated with protonation/deprotonation of the metal center (λ = 1.59 eV) and suggest that sluggish proton transfer kinetics hinder access to a concerted route. Rate constants for concerted PCET indicate that the concerted routes are asynchronous. Additionally, through quantification of the relative contributions of parallel stepwise and concerted mechanisms toward net product formation, the influence of various reaction parameters on reactivity are identified. This work underscores the importance of understanding the PCET mechanism for controlling metal hydride reactivity, which could lead to superior catalyst design for fuel production and oxidation.

Relating Franck-Condon blockade to redox chemistry in the single-particle picture.

In this work, we explore Franck-Condon blockade in the "redox limit," where nuclear relaxation processes occur much faster than the rate of electron transfer. To this end, the quantized rate expressions for electron transfer are recast in terms of a quantized redox density of states (DOS) within a single phonon mode model. In the high temperature regime, this single-particle picture formulation of electron transfer is shown to agree well with the semi-classical rate and DOS expressions developed by Gerischer and Hopfield. Upon incorporation into a two electrode formulation, utilizing the master equation approach, the low temperature quantized conductance features of Franck-Condon blockade are reproduced. Moreover, at sufficiently large reorganization energies, it is argued that Franck-Condon blockade should also be observable in room temperature systems. In general, this work aims to further bridge descriptions of electron transfer and transport in the single-particle picture.

Microfluidics-based super-resolution microscopy enables nanoscopic characterization of blood stem cell rolling.

Hematopoietic stem/progenitor cell (HSPC) homing occurs via cell adhesion mediated by spatiotemporally organized ligand-receptor interactions. Although molecules and biological processes involved in this multistep cellular interaction with endothelium have been studied extensively, molecular mechanisms of this process, in particular the nanoscale spatiotemporal behavior of ligand-receptor interactions and their role in the cellular interaction, remain elusive. We introduce a microfluidics-based super-resolution fluorescence imaging platform and apply the method to investigate the initial essential step in the homing, tethering, and rolling of HSPCs under external shear stress that is mediated by selectins, expressed on endothelium, with selectin ligands (that is, CD44) expressed on HSPCs. Our new method reveals transient nanoscale reorganization of CD44 clusters during cell rolling on E-selectin. We demonstrate that this mechanical force-induced reorganization is accompanied by a large structural reorganization of actin cytoskeleton. The CD44 clusters were partly disrupted by disrupting lipid rafts. The spatial reorganization of CD44 and actin cytoskeleton was not observed for the lipid raft-disrupted cells, demonstrating the essential role of the spatial clustering of CD44 on its reorganization during cell rolling. The lipid raft disruption causes faster and unstable cell rolling on E-selectin compared with the intact cells. Together, our results demonstrate that the spatial reorganization of CD44 and actin cytoskeleton is the result of concerted effect of E-selectin-ligand interactions, external shear stress, and spatial clustering of the selectin ligands, and has significant effect on the tethering/rolling step in HSPC homing. Our new experimental platform provides a foundation for characterizing complicated HSPC homing.

Modern Interdisciplinary and Interhospital Acute Stroke Therapy—What Patients Think About It and What They Really Understand

BackgroundAccess to reperfusion therapies in patients with large vessel occluding acute ischemic stroke demands process reorganization and optimization. Neurovascular networks are being built up to provide 24/7 endovascular stroke therapy service. In times of an increasingly complex stroke rescue chain little is known about patients’ and their relatives’ treatment awareness. MethodsAll patients, who received any kind of acute reperfusion treatment between January and August 2017 in the university hospital Aachen, and their proxies, were included in the survey. Patients were either primarily or secondarily transferred. ResultsFor all questions regarding stroke treatment patients and their caregivers provided concurring answers. 40% of both patients and caregivers did not understand the treatment that was performed. Finally, patients who perceived on their own that stroke detection was delayed had significantly longer onset to door times than patients who did not have this impression. ConclusionsThis study showed that patients’ and proxies’ answers correlated significantly. In case of patients’ unavailability extrapolation of treatment satisfaction from answers by proxies might be permitted. High percentages of patients and caregivers do not understand relevant information, possibly due to limits of communication in an emergency setting or deficits in communication during the hospital stay. More emphasis should be laid on providing further information during the hospital stay.

(Invited) Time Resolved EPR Study on Photoinduced Charge-Transfer Trap States in Thiophene-Thiazolothiazole Copolymers Films

Great attentions have been attracted on the organic photovoltaic (OPV) devices as the next generation thin-film solar cells that can be low-cost, flexible and light.[1] Conjugated polymers have extensively been utilized in various organic electronic devices including the solar cells, field-effect transistors (FET)[2] and light-emitting diodes[3] (LED). The spin coating method from mixed solutions consisting of the conjugated polymers as the electron donors (D) and fullerene derivatives as the acceptors (A) has been employed to produce the solid photoactive layer of the OPV cells.[1] In the organic photoactive layers, it is well known that the polymer molecules are self-organized to generate the bulk heterojunction (BHJ)[4] interfaces. Apart from the OPV applications, pristine films of the conjugated polymers are also utilized for the FET and LED applications.[5] The polymers usually form two dimensional lamellae structures as a result of close interchain packing interaction.[4] Such crystalline phases are known to play a key role for the mobilities of the charges and the excitons in the organic devices. Recent studies suggested that non-fluorescent CT characters exist as a competitive channel of the formation of emissive exciton-type states and determine the light emission efficiencies of the LED films.[5] Despite the significance of the non-fluorescent CT state, no study has experimentally characterized geometry and electronic character of the photoinduced CT state in the pristine polymer films. Consequently, the optoelectric properties of the polymer films have not been fully understood. In our previous study, the geometry and the electronic coupling in the charge-separated states were clarified as the transient radical pairs in regioregular poly(3-hexylthiophene)–fullerene (P3HT–C60) linked dyad molecules.[6] In this study, we have directly observed the photoinduced CT state for a pristine film by thiophene–thiazolothiazole copolymer (PTzBT–BOHD)[7] fabricated by the spin–coating method using time-resolved EPR (TREPR) method to characterize the orbital geometries, the electronic property of the polymer CT state. We show that a long-lived interchain CT states (P+• P–•) are generated as a trap state at disordered region as defects at a cryogenic temperature. We have characterized the interspin separation and the exchange coupling of the interchain CT states in the pristine polymer film of PTzBT–BOHD generated by the 532 nm laser excitation at T = 77 K. It has been revealed that the triplet CT state is generated at the disordered regions of the polymer films as the deep trap site via the triplet exciton. These stable charge−traps would be produced at the polymer defect site possessing the large reorganization energy of ≈ 1 eV. These characteristics of the trapped charges may limit the device performances in the OPV, FET and LED applications. Thus, the TREPR method can provide us with the informative optoelectronic and structural properties of the polymer films for evaluations, designs, and developments of the highly efficient OPV, FET and LED systems. G. Yu, J. Gao, J. C. Hummelen, F. Wudl and A. J. Heeger, Science 270 (1995) 1789.C. B. Nielsen and I. McCulloch, Prog. Polym. Sci. 38 (2013) 2053.I. F. Perepichka, D. F. Perepichka, H. Meng and F. Wudl, Adv. Mater. 17 (2005) 2281.Y. Kim, S. Cook, S. M. Tuladhar, S. A. Choulis, J. Nelson, J. R. Durrant, D. D. C. Bradley, M. Giles, I. Mcculloch, C. S. Ha and M. Ree, Nat. Mater. 5 (2006) 197.Z. J. Hu, A. P. Willard, R. J. Ono, C. W. Bielawski, P. J. Rossky and D. A. Vanden Bout, Nat. Commun. 6 (2015) 8246.T. Miura, R. Tao, S. Shibata, T. Umeyama, T. Tachikawa, H. Imahori and Y. Kobori, J. Am. Chem. Soc. 138 (2016) 5879.I. Osaka, M. Saito, T. Koganezawa and K. Takimiya, Adv. Mater. 26 (2014) 331.

Local protein solvation drives direct down-conversion in phycobiliprotein PC645 via incoherent vibronic transport

The mechanisms controlling excitation energy transport (EET) in light-harvesting complexes remain controversial. Following the observation of long-lived beats in 2D electronic spectroscopy of PC645, vibronic coherence, the delocalization of excited states between pigments supported by a resonant vibration, has been proposed to enable direct excitation transport from the highest-energy to the lowest-energy pigments, bypassing a collection of intermediate states. Here, we instead show that for phycobiliprotein PC645 an incoherent vibronic transport mechanism is at play. We quantify the solvation dynamics of individual pigments using ab initio quantum mechanics/molecular mechanics (QM/MM) nuclear dynamics. Our atomistic spectral densities reproduce experimental observations ranging from absorption and fluorescence spectra to the timescales and selectivity of down-conversion observed in transient absorption measurements. We construct a general model for vibronic dimers and establish the parameter regimes of coherent and incoherent vibronic transport. We demonstrate that direct down-conversion in PC645 proceeds incoherently, enhanced by large reorganization energies and a broad collection of high-frequency vibrations. We suggest that a similar incoherent mechanism is appropriate across phycobiliproteins and represents a potential design principle for nanoscale control of EET.

Ambipolarity and Dimensionality of Charge Transport in Crystalline Group 14 Phthalocyanines: A Computational Study

The charge transport properties of ten group 14 phthalocyanine crystals are investigated by means of kinetic Monte Carlo simulations based on experimental X-ray structures. All investigated materials are predicted to exhibit an ambipolar semiconducting behavior, with hole and electron mobilities lying in the range 0.1–1 cm2 V–1 s–1, showing their potential for organic electronic devices. The simulations also provide evidence that the dimensionality of charge transport in these materials can be finely tuned by substituting the phenoxy axial groups with fluorine atoms and by varying their number and positions; a complete substitution gives rise to two-dimensional transport for both electrons and holes. Most remarkably, one of the investigated compounds that incorporates iodine-phenoxy groups as axial substituents exhibits the largest mobilities for both electrons and holes, owing to large intermolecular couplings and low reorganization energies, and thus emerges as a highly promising one-dimensional semicon...