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The present work demonstrates a facile hydrothermal approach to synthesize lanthanide-doped carbon quantum dots (CQDs) with europium and/or gadolinium elements. Taking the advantage of broadband adsorption in the ultraviolet-visible region, the doped QDs are directly used as building blocks for photo-electrochemical (PEC)-type photodetectors (PDs) and their performance is systematically investigated under various conditions. The europium (Eu) and gadolinium (Gd) co-doped (C:EuGd) QDs exhibit better photo-response than the single-elemental doped ones and also show outstanding long-term stability. According to the apparent response to light from 350 to 400 nm, the C:EuGd QDs are demonstrated to hold great potential for narrow-band PDs. This work highlights the practical applications of lanthanide-doped CQDs for PDs, and the results are beneficial for the development of elemental-doped CQDs in general.

In the past decades, porphyrin analogues have attracted increasing attention in light of their unique properties and potential applications in various areas. In this work, novel nonconjugated thiophene-embedded N-confused homoporphyrins 1 and 2 as well as a fully-conjugated N-fused homoporphyrin 3 have been prepared through acid-catalyzed condensation reactions followed by oxidation. Both 1 and 2 comprise two meso-sp3-carbon atoms. However, they are insensitive to the air or common oxidants. Single crystal X-ray diffraction analysis reveals that 2 adopts a highly distorted boat-like conformation, with the NH moieties of two pyrrolic units pointing outwards and an O atom attached to the α position of the N-confused pyrrole unit. As a result, hydrogen-bonded dimers are formed through the intermolecular hydrogen bonds between the lactam-like moieties. In contrast to the highly distorted structure of 2, N-fused homoporphyrin 3 contains a unique 5,5,5–tricyclic fused ring, and thus demonstrates a relatively coplanar conformation except one inverted pyrrole unit. Because of the different structural characters, 3 exhibits F− binding behavior distinct from that of 1 and 2.

Probing the supramolecular chirality of assemblies and controlling their handedness are closely related to the origin of chirality at the supramolecular level and the development of smart materials with desired handedness. However, it remains unclear how achiral residues covalently bonded to chiral amino acids can function in the chirality inversion of supramolecular assemblies. Herein, we report macroscopic chirality and dynamic manipulation of chiroptical activity of hydrogels self-assembled from phenylalanine derivatives, together with the inversion of their handedness achieved solely by exchanging achiral substituents between oligo(ethylene glycol) and carboxylic acid groups. This helicity inversion is mainly induced by distinct stacking mode of the self-assembled building blocks, as collectively confirmed by scanning electron microscopy, circular dichroism, crystallography, and molecular dynamics calculations. Through this straightforward approach, we were able to invert the handedness of helical assemblies by merely exchanging achiral substituents at the terminal of chiral gelators. This work not only presents a feasible strategy to achieve the handedness inversion of helical nanostructures for better understanding of chiral self-assembly process in supramolecular chemistry but also facilities the development of smart materials with controllable handedness in materials science. MOE (Min. of Education, S’pore)

Stimulated emission depletion microscopy provides a powerful sub-diffraction imaging modality for life science studies. Conventionally, stimulated emission depletion requires a relatively high light intensity to obtain an adequate depletion efficiency through only light–matter interaction. Here we show efficient emission depletion for a class of lanthanide-doped upconversion nanoparticles with the assistance of interionic cross relaxation, which significantly lowers the laser intensity requirements of optical depletion. We demonstrate two-color super-resolution imaging using upconversion nanoparticles (resolution ~ 66 nm) with a single pair of excitation/depletion beams. In addition, we show super-resolution imaging of immunostained cytoskeleton structures of fixed cells (resolution ~ 82 nm) using upconversion nanoparticles. These achievements provide a new perspective for the development of photoswitchable luminescent probes and will broaden the applications of lanthanide-doped nanoparticles for sub-diffraction microscopic imaging., Upconversion nanoparticles, which do not suffer from the photophysical artifacts that limit fluorescent molecules, offer an exciting opportunity for biological super-resolution imaging. Here, Zhan et al. develop an efficient STED mechanism using optimized lanthanide upconversion nanoparticles, enabling cytoskeleton nanoscopic imaging.

Three recently synthesized copper(II) complexes with aroylhydrazones of trifluoroacetic and benzenecarboxylic acids (Dalton Trans., 2013, 42, 16878) have been computationally investigated by densit ...

Although organic light-emitting molecules have received a growing attention and applicability in modern bioimaging science, the design and control of complex photoluminescent properties in unimolecularly selective imaging remains a challenging topic. Considering that tunable multipathway imaging can be advantagedly connected with treatment processes in therapy, the integration of an azulene and a cyanostyryl moiety into one skeleton is carried out for the generation of in situ stimuli-responsive luminescent materials, with the aim to achieve tunable and effective emissions in distinct channels through smart molecular design on a single-molecular platform. This strategy takes advantage of 1) the Z/E isomerization of the cyanostyryl unit that can vary the push-pull effect of the substitution on azulene, accompanied by altering absorption and emission of individual excited states, and 2) an optimized excited-state regulation for opening a near infrared emissive channel and making up for a controllable dual-pathway luminescent system together with the utilization of visible emission. As exemplified by a demonstration of manipulating the luminescence at the cell level, the materials exhibit a superior application potential for unimolecularly selective imaging, labeling and probing events.

Phosphorescence is a phenomenon of delayed luminescence that corresponds to the radiative decay of the molecular triplet state. As a general property of molecules, phosphorescence represents a cornerstone problem of chemical physics due to the spin prohibition of the underlying triplet-singlet emission and because its analysis embraces a deep knowledge of electronic molecular structure. Phosphorescence is the simplest physical process which provides an example of spin-forbidden transformation with a characteristic spin selectivity and magnetic field dependence, being the model also for more complicated chemical reactions and for spin catalysis applications. The bridging of the spin prohibition in phosphorescence is commonly analyzed by perturbation theory, which considers the intensity borrowing from spin-allowed electronic transitions. In this review, we highlight the basic theoretical principles and computational aspects for the estimation of various phosphorescence parameters, like intensity, radiative rate constant, lifetime, polarization, zero-field splitting, and spin sublevel population. Qualitative aspects of the phosphorescence phenomenon are discussed in terms of concepts like structure-activity relationships, donor-acceptor interactions, vibronic activity, and the role of spin-orbit coupling under charge-transfer perturbations. We illustrate the theory and principles of computational phosphorescence by highlighting studies of classical examples like molecular nitrogen and oxygen, benzene, naphthalene and their azaderivatives, porphyrins, as well as by reviewing current research on systems like electrophosphorescent transition metal complexes, nucleobases, and amino acids. We furthermore discuss modern studies of phosphorescence that cover topics of applied relevance, like the design of novel photofunctional materials for organic light-emitting diodes (OLEDs), photovoltaic cells, chemical sensors, and bioimaging.

Objective: Internet-delivered cognitive behavioral therapy (ICBT) is recommended as an efficient treatment alternative for depression in primary care. However, only few previous studies have been conducted at primary care centers (PCCs). We evaluated long-term effects of ICBT treatment for depression compared to treatment as usual (TAU) in primary care settings. Design: Randomized controlled trial. Setting: Patients were enrolled at16 PCCs in south-west Sweden. Participants: Patients attending PCCs and diagnosed with depression (n = 90). Interventions: Patients were assessed by a primary care psychologist/psychotherapist and randomized to ICBT or TAU. The ICBT included an ICBT program consisting of seven modules and weekly therapist e-mail or telephone support during the 3-month treatment period. Main outcome measures: Questionnaires on depressive symptoms (BDI-II), quality of life (EQ-5D) and psychological distress (GHQ-12) were administered at baseline, with follow-ups at 3, 6 and 12 months. Antidepressants and sedatives use, sick leave and PCC contacts were registered. Results: Intra-individual change in depressive symptoms did not differ between the ICBT group and the TAU group during the treatment period or across the follow-up periods. At 3-month follow-up, significantly fewer patients in ICBT were on antidepressants. However, the difference leveled out at later follow-ups. There were no differences between the groups concerning psychological distress, sick leave or quality of life, except for a larger improvement in quality of life in the TAU group during the 0- to 6-month period. Conclusions: ICBT with weekly minimal therapist support in primary care can be equally effective as TAU among depressed patients also over a 12-month period. Clinical trial registration: The trial was registered in the Swedish Registry, researchweb.org, ID number 30511.

A bidipyrrin nickel complex was synthesized in a high yield by oxidatively coupling between the ligands in the corresponding 2:1 (L:M) type of dipyrrin nickel complex, and further demetallation afforded the free bidipyrrin ligand. Interestingly, when treating the bidipyrrin nickel complex or the free bidipyrrin with FeCl3 in CH2Cl2/MeOH, the symmetric di-α-methoxy bidipyrrin could be synthesized in a high yield, with two methoxy groups attached to the terminal pyrrolic α-positions. Moreover, the coordination of the unsubstituted and disubstituted bidipyrrins with Zn(OAc)2·2H2O afforded two similar M2L2 type of bidipyrrin helical complexes with different ligand conformations and different Zn⋯Zn distances of 5.353 and 3.357 A, respectively. The difference in the conformations may be related to the electrostatic repulsions between the methoxy substituents. These results indicate that the dyes based on helical bidipyrrin zinc complexes with tunable structures and photophysical properties may be developed simply by modulating the terminal α-substituents.

Four alkoxy-wrapped push-pull porphyrin dyes containing the phenothiazine derived donor and the ethynylbenzoic acid acceptor have been designed, synthesized and used as sensitizers for fabricating ...

Nacre-mimetic biocomposites made from the combination of montmorillonite clay and the hemicellulose xyloglucan give materials that retain much of their material properties even at high relative humidity. Here, a model composite system consisting of two clay platelets intercalated by xyloglucan oligomers was studied at different levels of hydration using molecular dynamics simulations, and compared to the pure clay. It was found that xyloglucan inhibits swelling of the clay at low water contents by promoting the formation of nano-sized voids that fill with water without affecting the material’s dimensions. At higher water contents the XG itself swells, but at the same time maintaining contact with both platelets across the gallery, thereby acting as a physical cross-linker in a manner similar to the role of XG in the plant cell wall.

CH−π interaction-assisted alignment of organic conjugated systems has played an important role to regulate molecular electronic and photophysical properties, whereas harnessing such a smart noncovalent interaction into the tuning of unimolecular complex emissive bands covering a wide spectral region remains a challenging research topic. Since the tuning for visible and near-infrared emissive properties in a single π-functional platform relates to its multicolor luminescent behaviors and potential superior application in analysis, bioimaging, and sensing, herein, we report a proportional control of the singlet and triplet emissions that cover visible and near-infrared spectral regions, respectively, can be straightforwardly achieved by CH−π interaction-assisted self-assembly at the unimolecular level. Employing an octathionaphthalene-based single luminophore as a prototype, we find that a strength-adjustable CH−π interaction-assisted self-assembly can be established in mixed DMF/H2O and in the film state. ...

Owing to their potential use in organic light-emitting diodes and field-effect transistors we present a theoretical study of a series of unsymmetrical azatrioxa[8]circulenes in order to explain the impact of outer substituents and benzoannelation on photophysical constants and aromaticity of these compounds in terms of spin–orbit coupling perturbation and magnetically-induced ring currents. It is argued that the S1–Tn inter-system crossing processes constitute the main deactivation pathways for the fluorescence quenching, something that is supported by a good agreement obtained with experimental data on fluorescence quantum yields. The concept of the gauge-including magnetically induced currents has been applied in order to estimate the role of substituents and benzoannelated fragments on the aromaticity and particularly on the overall balance between the diatropic “aromatic” and paratropic “antiaromatic” current strengths. While a variation of the substituents in the outer perimeter of the studied circulenes does not provide a clear effect on their aromaticity, it is demonstrated that an additional benzoannelation (π-extension) of the azatrioxa[8]circulene macrocycle induces a significant aromaticity enhancement.

The inability to utilize near infrared (NIR) light has posed a stringent limitation for the efficiencies of most single-junction photovoltaic cells such as dye-sensitized solar cells (DSSCs). Here, we describe a strategy to alleviate the NIR light harvesting problem by upconverting non-responsive NIR light in a broad spectral range (over 190 nm, 670–860 nm) to narrow solar-cell-responsive visible emissions through incorporated dye-sensitized upconversion nanoparticles (DSUCNPs). Unlike typically reported UCNPs with narrow and low NIR absorption, the organic dyes (IR783) anchored on the DSUCNP surface were able to harvest NIR photons broadly and efficiently, and then transfer the harvested energy to the inorganic UCNPs (typically reported), entailing an efficient visible upconversion. We show that the incorporation of DSUCNPs into the TiO2 photoanode of a DSSC is able to elevate its efficiency from 7.573% to 8.568%, enhancing the power conversion efficiency by about 13.1%. We quantified that among the relative efficiency increase, 7.1% arose from the contribution of broad-band upconversion in DSUCNPs (about ∼3.4 times higher than the highest previously reported value of ∼2.1%), and 6.0% mainly from the scattering effect of DSUCNPs. Our strategy has immediate implications for the use of DSUCNPs to improve the performance of other types of photovoltaic devices.

A self-recoverable mechanoconversion of multicolor luminescence was observed by crystallization-induced self-assembly. Such a self-assembly led to the formation of nanorods with different molecular stacking modes, thus making the phosphorescence/fluorescence proportion alterable. Therefore, multicolor luminescence of the single luminophore can be achieved by a straightforward reversible mechanical stimulus.

From the simple one-pot Vilsmeier formylation of 9-diphenylaminoanthracence, mono-, di- and tri-formyl products were successfully synthesized and the yields for the individual products can be optimized by varying the equivalents of the Vilsmeier reagent and changing the reaction temperature. The four obtained aldehydes exhibit distinct optical properties, with the emission maxima varying in a large wavelength range of 455–593 nm, despite their similar structures. The intramolecular charge transfer effect can be effectively modulated by varying the numbers and positions of the formyl groups, resulting in the observed distinct optical properties. Based on the aldehydes, the corresponding boron-dipyrromethenes were also synthesized. Similarly, the intramolecular charge transfer effect and the optical properties can be effectively modulated by the numbers and positions of the boron-dipyrromethene moieties. To further modulate the intramolecular charge transfer effect and red shift the emission, the dimethoxy-substituted 9-diphenylaminoanthracence was also used for synthesizing the corresponding aldehyde and boron-dipyrromethene. Thus, full color emissions within the wavelength range of 455–704 nm were successfully achieved based on modulating the intramolecular charge transfer.

A combination of aggregation-induced emission and intramolecular charge transfer was achieved by using a triphenylamine analogue and a dicyanovinyl moiety as the electron donating and accepting uni ...

Lanthanide-doped upconversion nanoparticles (UCNPs) are increasingly used as luminescent candidates in multiplexing applications due to their excellent optical properties. In the past, several encoding identities have been proposed for UCNPs, including emission colour, intensity ratio between different emission bands, colour spatial distribution, and luminescence lifetime. In this paper, a new optical encoding dimension for upconversion nanomaterials is developed by exploring their luminescence kinetics, i.e., the phase angle of upconversion luminescence in response to a harmonic-wave excitation. Our theoretical derivation shows that the phase angle is governed jointly by the rise and decay times, characterizing the upconversion luminescence kinetics. Experimentally, a full set of methods are developed to manage the upconversion luminescence kinetics, through which the rise and decay times can be manipulated dependently or independently. Furthermore, a large phase-angle space is achieved in which tens of unique codes can potentially be generated in the same colour channel. Our work greatly extends the multiplexing capacity of UCNPs, and offers new opportunities for their applications in a wide range such as microarray assays, bioimaging, anti-counterfeiting, deep tissue multiplexing labelling/detection and high-density data storage. In addition, the development of this luminescence kinetics-based optical encoding strategy is also instructive for developing multiplexing techniques using other cascade luminescent systems that inherently lack multi-spectral channels, such as triplet-triplet annihilation molecule pairs.

This communication presents a structure–property study of a few novel pyridine-based difluoroborate compounds with a N–BF2–O core, which exhibit outstanding fluorescence properties. To exploit their potential for two-photon bioimaging, relationships between the two-photon action cross section and systematic structural modifications have been investigated and unravelled.

A great deal of effort has been devoted to developing gated photochromic systems due to their advantages in the smart materials and opto-electronic fields, whereas the gating function through certain ions has rarely been addressed. Since the photochromic materials gated by ions can be readily further processed into a multi-functional molecular switch and probe, we herein designed and conveniently synthesized a star-shaped Schiff-based diarylethene derivative showing typical photochromic properties in solution. This compound possesses two response channels (colorimetric and fluorogenic) to Cu2+ ions with photoswitching characteristics, making it a viable photochromic probe. It is noteworthy that its photochromic reactivity can be locked when Cu2+ ions are introduced into the solution. Moreover, the photoinactive and photoactive states can be interchanged reversibly by binding Cu2+ ions and unbinding Cu2+ ions using EDTA, which shows promise for application in multi-controlled molecular switches and smart materials. The mechanism of the photochromic properties locked by Cu2+ ions is reasonably proposed by theoretical simulations. These results could be valuable for the further development of molecular switching systems with multiple stimuli responses.

We explore the use of substituent-sensitive balance between fluorescence and non-radiative decay as a tool for optical tuning of promising materials for organic light emitting diode applications. A series of N-butylated tetrabenzotetraaza[8]circulenes is studied computationally in order to explain the gradual decrease of fluorescence intensity with the increase of the substituent number. The inter-system crossing probability is found to increase upon the gradual substitution of the circulene macrocycle as a result of the decrease of the S1–T1 energy gap due to the deformation of the tetrabenzotetraaza[8]circulenes and therefore the distortion of the π-conjugation within the macrocycles. In contrast, the S1–T1 spin–orbit coupling matrix elements are quite insensitive to the number of outer substituents. As a result, the fluorescence-responsible ππ* transition becomes less intense and the fluorescence rate constant decreases.

Core–valence double-electron ionisation spectra of a few small molecules – carbon monoxide, ammonia, methyl fluoride and thiophene – are presented and analysed using the self-consistent field algorithm introduced by Hans Jorgen Jensen 30 years ago. It confirms the utility of this algorithm, frequently employed to obtain stable and sharp convergence of wave functions for the benefit of calculations of a great variety of molecular properties, thus also for optimisation of core–valence states and for the interpretation of the corresponding spectra.

Collective lattice resonances (CLRs) in finite-sized $ 2D $2D arrays of dielectric nanospheres have been studied via the coupled dipole approximation. We show that even for sufficiently large arrays, up to $ 100 \times 100 $100×100 nanoparticles (NPs), electric or magnetic dipole CLRs may differ significantly from the ones calculated for infinite arrays with the same NP sizes and interparticle distances. The discrepancy is explained by the existence of a sufficiently strong cross-interaction between electric and magnetic dipoles induced at NPs in finite-sized lattices, which is ignored for infinite arrays. We support this claim numerically and propose an analytic model to estimate a spectral width of CLRs for finite-sized arrays. Given that most of the current theoretical and numerical researches on collective effects in arrays of dielectric NPs rely on modeling infinite structures, the reported findings may contribute to thoughtful and optimal design of inherently finite-sized photonic devices.

The recently synthesized twisted thia-norhexaphyrin and its multiply annulated polypyrrolic derivatives have been studied computationally. Gauge-including magnetically induced current calculations predict a global nonaromatic character of the initial thia-norhexaphyrin due to the highly-twisted conformation of the macrocycle. Upon the oxidation of the thia-norhexaphyrin four multiply annulated polypyrrolic aromatic macrocycles are formed for which the global aromatic character is confirmed in agreement with experimentally measured

The fundamental properties of recently synthesized single- and bilayer ${\mathrm{PdSe}}_{2}$ are investigated using accurate many-body perturbation GW theory to quantitatively examine their electronic structure and explain the insufficiency of previously reported experimental and theoretical results. Including electron-hole interactions responsible for exciton formation, we solve the Bethe-Salpeter equation on top of the ${\mathrm{GW}}_{0}$ approximation to predict the optical properties. The fundamental quasiparticle band gaps of single- and bilayer ${\mathrm{PdSe}}_{2}$ are 2.55 and 1.89 eV, respectively. The optical gap of monolayer ${\mathrm{PdSe}}_{2}$ reduces significantly due to a large excitonic binding energy of 0.65 eV comparable to that of ${\mathrm{MoSe}}_{2}$, while an increase of the layer number decreases the excitonic binding energy to 0.25 eV in bilayer ${\mathrm{PdSe}}_{2}$. The giant band gap renormalization of \ensuremath{\sim}36--38% in the bilayer (BL) ${\mathrm{PdSe}}_{2}$/graphene heterostructure has a high impact on the construction of ${\mathrm{PdSe}}_{2}$-based devices and explains the experimentally observed band gap. The small value of the experimental optical gap of single-layer (SL) ${\mathrm{PdSe}}_{2}$ (1.3 eV) can be explained by the presence of Se vacancies, which can drop the Tauc-estimated optical gap to \ensuremath{\sim}1.32 eV. The absorption spectra of both mono- and bilayer ${\mathrm{PdSe}}_{2}$ cover a wide region of photon energy, demonstrating promising application in solar cells and detectors. These findings provide a basis for a deeper understanding of the physical properties of ${\mathrm{PdSe}}_{2}$ and ${\mathrm{PdSe}}_{2}$-based heterostructures.

A series of Zn(ii) complexes with 5-(4

Expanded porphyrins have been attracting increasing attention owing to their unique optical and electrochemical properties as well as switchable aromaticity. Toward material applications, regioselective functionalization of the expanded porphyrins at their periphery is indeed challenging due to the presence of multiple reactive sites. Herein, a set of regioselective halogenated isomers (L5-Br-A/B/C) of neo-confused isosmaragdyrin (L5) are synthesized by a combination of the halogenation reaction of L5 and sequential macrocycle-to-macrocycle transformation reactions of its halogenated isomers. On this basis, the regioselectively functionalized isosmaragdyrins are utilized as building blocks for constructing multichromophoric porphyrinoids, specifically, heterodyads L5-ZnP-A/B/C, in which a common zinc porphyrin is linked at three different pyrrolic positions of isosmaragdyrins, respectively, by Sonogashira coupling reactions. The highly efficient energy cascade from porphyrin to isosmaragdyrin is elucidated using steady-state/time-resolved spectroscopies and theoretical calculations. Notably, the energy transfer processes from the porphyrin to the isosmaragdyrin moieties as well as the excitation energy transfer rates in L5-ZnP-A/B/C are highly dependent on the linking sites by through-bond and Forster-type resonance energy transfer mechanisms. The site-selective functionalization and subsequent construction of a set of heterodyads of the expanded porphyrinoid would provide opportunities for developing new materials for optoelectronic applications.

In this study, we systematically investigate the decay characteristics of upconversion luminescence (UCL) under anti-Stokes excitation through numerical simulations based on rate-equation models. We find that a UCL decay profile generally involves contributions from the sensitizer's excited-state lifetime, energy transfer and cross-relaxation processes. It should thus be regarded as the overall temporal response of the whole upconversion system to the excitation function rather than the intrinsic lifetime of the luminescence emitting state. Only under certain conditions, such as when the effective lifetime of the sensitizer's excited state is significantly shorter than that of the UCL emitting state and of the absence of cross-relaxation processes involving the emitting energy level, the UCL decay time approaches the intrinsic lifetime of the emitting state. Subsequently, Stokes excitation is generally preferred in order to accurately quantify the intrinsic lifetime of the emitting state. However, possible cross-relaxation between doped ions at high doping levels can complicate the decay characteristics of the luminescence and even make the Stokes-excitation approach fail. A strong cross-relaxation process can also account for the power dependence of the decay characteristics of UCL. QC 20190318

Visualized sensing through fluorescence signals is a powerful method for chemical and physical detection. However, the utilization of fluorescent molecular probes still suffers from lack of precise signal self-calibration in practical use. Here we show that fluorescence and thermally activated delayed fluorescence can be simultaneously produced at the single-molecular level. The thermally activated delayed fluorescence serves as a sensing signal with its wavelength and lifetime both altered correlating to polarity, whereas the fluorescence always remains unchanged as an internal reference. Upon the establishment of a three-dimensional working curve upon the ratiometric wavelength and photoluminescence lifetime vs. polarity, disturbance factors during a relevant sensing process can be largely minimized by such a multiple self-calibration. This strategy was further applied into a precise detection of the microenvironmental polarity variation in complex phospholipid systems, towards providing new insights for convenient and accurate diagnosis of membrane lesions., New photoluminescent strategies are required to realize high-performance ratiometric sensors for bio-sensing applications. Here, the authors demonstrate a fluorescence-thermally activated delayed fluorescence dual emission strategy for ratiometric sensors with high precision.

The amyloid β (Aβ) fibril is a hallmark of Alzheimer's disease (AD) and has therefore served as an important target for early diagnosis of AD. The Pittsburgh Compound-B (PiB) is one of the most famous positron emission tomography (PET) tracers commonly used for in vivo detection of Aβ fibrils. Many theoretical studies have predicted the existence of various core binding sites with different microenvironments for probes binding to the Aβ fibril. However, little attention has been devoted to how the probes actually penetrate into the different core binding sites. In this study, an integrated molecular modeling scheme is used to study the penetration of PiB into the core binding sites of the Aβ

We review recent work on property decomposition techniques using quantum chemical methods and discuss some topical applications in terms of quantum mechanics-molecular mechanics calculations and the constructing of properties of large molecules and clusters. Starting out from the so-called LoProp decomposition scheme [Gagliardi et al., J. Chem. Phys., 2004, 121, 4994] for extracting atomic and inter-atomic contributions to molecular properties we show how this method can be generalized to localized frequency-dependent polarizabilities, to localized hyperpolarizabilities and to localized dispersion coefficients. Some applications of the generalized decomposition technique are reviewed - calculations of frequency-dependent polarizabilities, Rayleigh scattering of large clusters, and calculations of hyperpolarizabilities of proteins.

Photocurrent (Jsc) and photovoltage (Voc) are two important parameters for dye-sensitized solar cells (DSSCs) to achieve high power conversion efficiencies (PCEs). Herein, we synthesize four novel ...

CdTe/CdS core-shell quantum dots were synthesized and implemented into a light emitting device resulting in multi-channel electroluminescence with a light-green emission colour. The main electroluminescence band at about 530 nm corresponds to the emission by the CdTe core (type I core/shell structure), while the next emission band at 595 nm is assigned to the crossed recombination of electrons from the conduction band of the CdS shell and holes from the valence band of the CdTe core (type II core/shell structure). At the same time, the photoluminescence spectrum of the synthesized CdTe/CdS core-shell quantum dots contains only one emission band distinctive for type II structures. This behavior of CdTe/CdS core-shell quantum dots upon the electroexcitation allows the extension of the electroluminescence spectrum in the optical region in a way that is useful for the lighting-source applications. Such multi-channel electroluminescence can most probably also be reproduced in related core-shell systems accounting for size-confinement between the core size and shell thickness.

Purpose Several tracers have been designed for tracking the abnormal accumulation of tau pathology in vivo. Recently, concerns have been raised about the sources of off-target binding for these tracers; inconclusive data propose binding for some tracers to monoamine oxidase B (MAO-B). Methods Molecular docking and dynamics simulations were used to estimate the affinity and free energy for the binding of several tau tracers (FDDNP, THK523, THK5105, THK5317, THK5351, T807 [aka AV-1451, flortaucipir], T808, PBB3, RO-948, MK-6240, JNJ-311 and PI-2620) to MAO-B. These values were then compared with those for safinamide (MAO-B inhibitor). PET imaging was used with the tau tracer [18F]THK5317 and the MAO-B tracer [11C]DED in five patients with Alzheimer’s disease to investigate the MAO-B binding component of this first generation tau tracer in vivo. Results The computational modelling studies identified a binding site for all the tau tracers on MAO-B; this was the same site as that for safinamide. The binding affinity and free energy of binding for the tau tracers to MAO-B was substantial and in a similar range to those for safinamide. The most recently developed tau tracers MK-6240, JNJ-311 and PI-2620 appeared, in silico, to have the lowest relative affinity for MAO-B. The in vivo investigations found that the regional distribution of binding for [18F]THK5317 was different from that for [11C]DED, although areas of suspected off-target [18F]THK5317 binding were detected. The binding relationship between [18F]THK5317 and [11C]DED depended on the availability of the MAO-B enzyme. Conclusions The developed tau tracers show in silico and in vivo evidence of cross-interaction with MAO-B; the MAO-B component of the tracer binding was dependent on the regional concentration of the enzyme. Electronic supplementary material The online version of this article (10.1007/s00259-019-04305-8) contains supplementary material, which is available to authorized users.

A series of thia[7]circulenes and novel Se-, Te-, S/Te-, and Se/Te-substituted [8]circulenes have been studied by calculations of nucleus-independent chemical shift indices and gauge including magnetically induced currents to interpret the impact of heteroatoms on the aromatic properties of these polyheterocyclic species. The calculations indicate that all the studied hetero[7]circulenes and hetero[8]circulenes consist of two concentric subsystems: an inner seven- or eight-membered core is antiaromatic because of the existence of a paratropic ring current, and an outer system of benzene and hetarene rings that exhibit aromatic behaviour due to the circulation of diatropic ring currents. Thus, most of the hetero[7]circulenes can be considered as slightly antiaromatic because of the slight domination of the paratropic ring currents over the diatropic ones, whereas hetero[8]circulenes represent aromatic species due to the prevailing contribution of the diatropic currents. The antiaromaticity gradually increases with more scattered arrangements of the thiophene and benzene rings in each series of di-, tri-, tetra-, and pentathia[7]circulenes because of the reduced conjugation effect between the neighboring thiophene and benzene rings. Loss of planarity with increased strain leads to an increased antiaromatic character of the lower representatives of the thia[n]circulenes, whereas higher thia[n]circulenes demonstrate a more pronounced aromatic nature because of the small deviation from planarity. The ring current topology is found to be quite insensitive to the heteroatom type, number of hetarene rings and the size of the inner ring; this clearly manifests the special electronic structure of hetero[n]circulenes containing two concentric cyclic subsystems.

We report on a combined theoretical and experimental study of core excitation spectra of gas and liquid phase methanol as obtained with the use of X ray absorption spectroscopy XAS and resonant inelastic X ray scattering RIXS . The electronic transitions are studied with computational methods that include strict and extended second order algebraic diagrammatic construction [ADC 2 and ADC 2 x], restricted active space second order perturbation theory, and time dependent density functional theory providing a complete assignment of the near oxygen K edge XAS. We show that multimode nuclear dynamics is of crucial importance for explaining the available experimental XAS and RIXS spectra. The multimode nuclear motion was considered in a recently developed mixed representation where dissociative states and highly excited vibrational modes are accurately treated with a time dependent wave packet technique, while the remaining active vibrational modes are described using Franck Condon amplitudes. Particular attention is paid to the polarization dependence of RIXS and the effects of the isotopic substitution on the RIXS profile in the case of dissociative core excited states. Our approach predicts the splitting of the 2a amp; 8243; RIXS peak to be due to an interplay between molecular and pseudo atomic features arising in the course of transitions between dissociative core and valence excited states. The dynamical nature of the splitting of the 2a amp; 8243; peak in RIXS of liquid methanol near pre edge core excitation is shown. The theoretical results are in good agreement with our liquid phase measurements and gas phase experimental data available from the literature

In the present paper we describe the first synthesis and evaluation of a novel Mn (II) complex (DTPA-PPDA Mn (II)) which contains a C-15 fatty acid moiety that has high affinity to the heart muscle. The complexation energy of DTPA-PPDA Mn (II) evaluated by quantum chemistry methodology indicates that it essentially exceeds the corresponding value for the known DTPA Mn (II) complex. Molecular docking revealed that the affinity of the designed complex to the heart-type transport protein H-FABP well exceeds that of lauric acid. Phantom experiments in low-field MRI the designed contrast agent provides MR imaging comparable to gadopentetic acid.

Positron emission tomography (PET) tracers play an important role in the diagnosis of Alzheimer’s disease, a condition that leads to progressive dementia and memory loss. A high binding affinity and specificity of the PET tracers to amyloid oligomers and fibrils are crucial for their successful application as diagnostic agents. In this sense, it is essential to design PET tracers with enhanced binding affinities, which can lead to more precise and earlier detection of Alzheimer’s disease conditions. The application of in silico methodology for the design and development of efficient PET tracers may serve as an important route to improved Alzheimer’s disease diagnosis. In this work, the performance of widely used computational methods is explored for predicting experimental binding affinities of styrylbenzoxazole (SB) derivatives against a common amyloid protofibril. By performing docking, molecular dynamics, and quantum chemistry calculations in sequence their combined predictive performance is explored. ...

By oxidation of an alternately N-confused bilane in CH2Cl2, a C–N fused tetrapyrrin was synthesized that bears a 5.5.5-tricyclic ring generated from an intramolecular C–N linkage. When CH3CN was used as the reaction medium, a multiply C–N-fused octapyrrolic dimer was also obtained that contained two 5.5.5.7.5-pentacyclic moieties and a bipyrrole unit generated from the intramolecular C–N linkage and intermolecular C–C linkage, respectively. This could be coordinated with Ni(acac)2 to afford a mixed-ligand complex.

Two recently synthesized copper(II) complexes with spacer-armed bispicolylamidrazone ligands have been theoretically studied at the density functional theory (DFT) level accounting for empirical dispersion correction and intrinsic anionic environment by perchlorate ions. The exchange parameter between the open-shell singlet and triplet states of the studied complexes has been estimated by broken symmetry DFT calculations. The mechanism of spin-spin exchange interaction between the unpaired electrons via the σ-bond aliphatic chain (Gusev et al., 2015) is confirmed. Instead, a anion-induced mechanism is proposed which means that the anionic grid participates in the exchange interaction between the unpaired electrons.

Efficient Broadband Upconversion of Near-Infrared Light in Dye-Sensitized Core/Shell Nanocrystals

The design of molecular probes and tracer molecules with specificity toward amyloid beta (Aβ) fibrils is of paramount importance for the selective diagnosis of Alzheimer's disease. This requires a detailed understanding of the binding sites in amyloid targets, their number, and their binding mechanism for various tracer molecules. We adopt an integrated approach including molecular docking, molecular dynamics, and generalized Born-based free energy calculations to investigate site-specific interactions of different amyloid binding molecules. Our study reproduces the experimental results on the relative binding affinity of the tracers and amyloid binders and explains the feature of "multiple binding sites" in amyloid targets as probed by competition binding experiments. A major outcome of this study is that it is the core sites of the Aβ fibrils that are responsible for the experimentally reported binding profiles of tracers in amyloid targets rather than the surface sites that received much focus in earlier investigations.

Rayleigh scattering of naturally polarized light was studied for systems with atmospheric relevance representing growing water clusters with adsorbed cis-pinonic acid. The scattering intensity was computed from the static and dynamical polarizabilities of the clusters obtained by a recently derived methodology for classical polarizabilities, in which Applequist equations for interacting polarizable dipoles are used together with point-dipoles and polarizabilities obtained by quantum chemistry and decomposed into the atomic domain by the so-called LoProp transformation generalized for frequency dependence. The Applequist interaction was found to yield scattering intensities 20% larger for a cluster consisting of 1000 water molecules, as compared to the method where all of the polarizabilities of molecules are added without interactions. It was confirmed that scattering intensity depends quadratically on the number of water molecules in the cluster, and that it also increases quadratically with increase in the mass constituent of the foreign substance. The adsorption of the cis-pinonic acid increases the contribution to the scattering intensity stemming from the anisotropic polarizability, as compared to the isotropic contribution. The ramifications of the method in predicting Rayleigh scattering and the earth's albedo with respect to man-made and natural gas emission are briefly discussed.

A functional C3-symmetric benzene-1,3,5-tricarboxamide-anchored diarylethene molecule (C3-BTE) is synthesized, which evolves into ordered superstructures with tunable morphology properties both in different solvent and via alternative light stimuli. The formation of rod-like assemblies from C3-BTE is reported and the self-assembly property of C3-BTE can be realized through alternative light stimuli in nonpolar solvents such as toluene.

To rationalize the effects of intramolecular steric hindrance on the performance of diarylethene photoswitches, we here present a density functional theory study on the thermal bistability and optical properties of a photochromic diarylethene BBTE consisting of a benzobis(thiadiazole) bridge and benzothiophene rings, in which prominent steric hindrance exists owing to the extended structures of π-conjugated groups. Our calculations not only provide rational explanations for the isolation of enantiopure anti-parallel conformers of the open-ring isomer, but also elucidate the detailed pathway of a two-step ground-state ring-opening process, where the thermal stability of the closed-ring isomer is guaranteed by an overall free energy barrier of around 113 kJ mol −1 (27 kcal mol −1 ). In addition, the tunable intramolecular charge transfer of the donor–acceptor structure formed by the benzobis(thiadiazole) bridge and the bulky benzothiophene rings is also addressed within time-dependent density functional theory. Charge transfer excitations in the open- and the closed-ring isomers are characterized as long-range and medium-range, respectively. We show that the diarylethene derivative under investigation can serve as a promising platform for future development of optoelectronic materials.

Organic near-infrared (NIR) fluorescent probes have been recognized as an emerging class of materials exhibiting a great potential in advanced bioanalytical applications. However, synthesizing such organic probes that could simultaneously work in the NIR spectral range and have large Stokes shift, high stability in biological systems, and high photostability have been proven challenging. In this work, aggregation induced excimeric NIR emission in aqueous media was observed from a suitably substituted perylene monoimide (PeIm) dye. Controlled entrapment of the dye into pluronic F127 micellar system to preserve its monomeric green emission in aqueous media was also established. The aggregation process of the PeIm dye to form organic nanoparticles (NPs) was evaluated experimentally by the means of transmission electron microscope imaging as well as theoretically by the molecular dynamics simulation studies. Tuning the morphology along with the formation of colloidosomes by the controlled self-aggregation of PeIm NPs in aqueous suspension was demonstrated successfully. Finally, both excimeric and monomeric emissive PeIm NPs as well as PeIm colloidosomes were employed for the bioimaging in vitro.

We propose and evaluate algorithms for the calculation of molecular polarizabilities and hyperpolarizabilities of extended chemical systems. These algorithms are generalizations of the Silberstein-Applequist procedure involving interacting induced classical dipoles through the localized polarizabilities and hyperpolarizabilities. The models are evaluated in terms of interacting molecular units as well as interacting atomic units that result from the atomic decomposition scheme known as the LoProp transformation. We introduce a generalized LoProp scheme which applies to hyperpolarizabilities as well as to polarizabilities. The accuracy of the second-order Applequist method is tested for the first hyperpolarizability for the TIP3P water model using both Hartree-Fock and density functional theory evaluated with different basis sets. Possible applications and ramifications of the scheme are discussed.