Self-assembled Co(II) and Co(III) [M2L3] helicates and [M4L6] tetrahedra from an unsymmetrical quaterpyridine ligand.

In order to bind guest molecules with exquisite selectivity, biological host molecules often employ low symmetry binding pockets. The majority of metallosupramolecular assemblies, however, rely on symmetrical ligands to form high-symmetry assemblies that enclosing similarly symmetrical cavities. Here we employ an unsymmetrical quaterpyridine ligand in combination with cobalt(II) to form a mixture of low-symmetry [M2L3] helicates and [M4L6] tetrahedra and their subsequent oxidation to Co(III)-containing assemblies.

Tamm plasmon polariton-based planar hot-electron photodetector for the near-infrared region.

Light-trapping devices have always been a topic of intense interest among researchers. One such device that has gained attention is the hot-electron photodetector with a tunable detection wavelength. Photodetectors based on plasmon nanostructures that provide excitation of surface plasmon polaritons are challenging to manufacture. To address this issue, a planar hot-electron photodetector based on a Tamm plasmon polariton localized in a metal-semiconductor-multilayer mirror structure has been proposed in this study. The parameters and materials of the structure were adjusted to ensure perfect absorption at the resonance wavelength. As a result, the photoresponsivity of the proposed device can reach 42.6 mA W-1 at 905 nm. For the first time, the photosensitivity was calculated analytically by solving the dispersion law for the Tamm plasmon polariton.

Remote stereocentres do not disrupt the stereochemical coupling in homochiral [M2L3] helicates and [M4L6] tetrahedra.

Despite the use of achiral ligands, the vast majority of metallosupramolecular assemblies containing octahedral tris-bidentate metal centres show strong stereochemical communication between metal centres, generally resulting in homochiral assemblies even though they are statistically disfavoured. Here we show that when resolved stereocentres are attached to the central part of a quaterpyridine ligand, the stereochemical coupling from this centre is insufficient to disrupt the strong stereochemical communication between metal centres in both [M2L3] helicates and [M4L6] tetrahedra.

Wavelength- and Angle-Selective Photodetectors Enabled by Graphene Hot Electrons with Tamm Plasmon Polaritons.

Recently, two-dimensional materials have attracted attention owing to their special optical characteristics and miniaturization, with low thickness as well as extremely high responsivity. Additionally, Tamm plasmon polariton (TPP) resonance can be observed by combining a metal film and a one-dimensional (1D) photonic crystal (PC), where an electric field confinement is located at the metal-1D PC interface. In this study, a graphene layer combined with a TPP is proposed as a wavelength- and angle-selective photodetector. The graphene layer is located where the strong field confinement occurs, and the photocurrent response is significantly enhanced with increasing absorption by over four times (from 62.5 µA⋅W-1 to 271 µA⋅W-1 and undetected state to 330 µA⋅W-1 in two different samples). Moreover, the graphene-TPP photodetector has wavelength and angle selectivity, which can be applied in LiDAR detecting, sun sensors, laser beacon tracking, and navigational instruments in the future.

Facile Synthesis of PdO.TiO2 Nanocomposite for Photoelectrochemical Oxygen Evolution Reaction.

The rapid depletion of fossil fuels and environmental pollution has motivated scientists to cultivate renewable and green energy sources. The hydrogen economy is an emerging replacement for fossil fuels, and photocatalytic water splitting is a suitable strategy to produce clean hydrogen fuel. Herein, the photocatalyst (PdO.TiO2) is introduced as an accelerated photoelectrochemical oxygen evolution reaction (OER). The catalyst showed significant improvement in the current density magnitude from 0.89 (dark) to 4.27 mA/cm2 (light) during OER at 0.5 V applied potential. The as-synthesized material exhibits a Tafel slope of 170 mVdec-1 and efficiency of 0.25% at 0.93 V. The overall outcomes associated with the photocatalytic activity of PdO.TiO2 demonstrated that the catalyst is highly efficient, thereby encouraging researchers to explore more related catalysts for promoting facile OER.

Nanostructured photosensitive layer for Tamm-plasmon-polariton-based organic solar cells.

The influence of the volume fraction of plasmonic nanoparticles on the efficiency of the Tamm-plasmon-polariton-based organic solar cell is investigated in the framework of temporal coupled mode theory and confirmed by the transfer matrix method. It is shown that, unlike a conventional plasmonic solar cell, in which the efficiency is directly proportional to the volume fraction of nanoparticles in the photosensitive layer, the efficiency of the proposed solar cell reaches the highest value at low volume fractions. This effect is explained by the fact that at these volume fractions, the critical coupling condition of the incident field with the Tamm plasmon polariton is fulfilled. Thus, for the incoming radiation range of 350 to 500 nm, a maximal cell efficiency of 28% is achieved with a volume fraction of nanoparticles equal to 10%. Additionally, the optical properties of the photosensitive layer are compared for the cases of determining its complex refractive index by effective medium theory and the S-parameter retrieval method. A good agreement between the results is demonstrated, which encourages the use of the effective medium theory for preliminary calculations.

Double-Resolved Beam Steering by Metagrating-Based Tamm Plasmon Polariton.

We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The tunability of the phase and amplitude of the reflected wave arises from modulation of the refractive index of a transparent conductive oxide layer by applying the bias voltage. The electrical switching of diffracted beams of the ±1st order is shown. The possibility of doubling the angular resolution of beam steering by using asymmetric reflected phase distribution with integer and half-integer periods of the metagrating is demonstrated.

Sterics and metal-ion radius control the self-assembly of [M2L3] helicates.

The interplay of many factors influences the outcomes of self-assembly reactions. Using an acetylene-appended quaterpyridine ligand we show that both the size of the metal ion and the presence of steric repulsion between the acetylene groups result in the exclusive formation of [M2L3] helicates rather than a helicate/tetrahedron equilibrium.

Broadband Tamm Plasmons in Chirped Photonic Crystals for Light-Induced Water Splitting.

An electrode of a light-induced cell for water splitting based on a broadband Tamm plasmon polariton localized at the interface between a thin TiN layer and a chirped photonic crystal has been developed. To facilitate the injection of hot electrons from the metal layer by decreasing the Schottky barrier, a thin n-Si film is embedded between the metal layer and multilayer mirror. The chipping of a multilayer mirror provides a large band gap and, as a result, leads to an increase in the integral absorption from 52 to 60 percent in the wavelength range from 700 to 1400 nm. It was shown that the photoresponsivity of the device is 32.1 mA/W, and solar to hydrogen efficiency is 3.95%.

Metal-Dielectric Polarization-Preserving Anisotropic Mirror for Chiral Optical Tamm State.

This numerical study demonstrates the possibility of exciting a chiral optical Tamm state localized at the interface between a cholesteric liquid crystal and a polarization-preserving anisotropic mirror conjugated to a metasurface. The difference of the proposed structure from a fully dielectric one is that the metasurface makes it possible to decrease the number of layers of a polarization-preserving anisotropic mirror by a factor of more than two at the retained Q-factor of the localized state. It is shown that the proposed structure can be used in a vertically emitting laser.

Controlling the Complexity and Interconversion Mechanisms in Self-Assembled [Fe2 L3 ]4+ Helicates and [Fe4 L6 ]8+ Cages.

Self-assembled coordination cages and metal-organic frameworks have relied extensively on symmetric ligands in their formation. Here we have prepared a relatively simple system employing an unsymmetric ligand that results in two distinct self-assembled structures, a [Fe2 L3 ]4+ helicate and a [Fe4 L6 ]8+ cage composed of 10 interconverting diastereomers and their enantiomers. We show that the steric profile of the ligand controls the complexity, thermodynamics and kinetics of interconversion of the system.

Chiral-Selective Tamm Plasmon Polaritons.

Chiral-selective Tamm plasmon polariton (TPP) has been investigated at the interface between a cholesteric liquid crystal and a metasurface. Different from conventional TPP that occurs with distributed Bragg reflectors and metals, the chiral-achiral TPP is successfully demonstrated. The design of the metasurface as a reflective half-wave plate provides phase and polarization matching. Accordingly, a strong localized electric field and sharp resonance are observed and proven to be widely tunable.

Photosensitivity and reflectivity of the active layer in a Tamm-plasmon-polariton-based organic solar cell.

We report on a model of an organic solar cell in which a photosensitive layer doped with plasmon nanoparticles acts as not only an absorbing element but also a mirror involved in the formation of the Tamm plasmon polariton. It is shown that such solar cells can be fabricated without metal contacts, thus avoiding undesired losses in the system. Methods for an additional increase in the integral absorption by applying metal or dielectric mirrors to the lower boundary of the photonic crystal are proposed. It has been found that the integral absorption in the active layer can be increased by 15% compared to classical optimized planar solar cells.

Strain Sensor via Wood Anomalies in 2D Dielectric Array.

Optical sensing is one of many promising applications for all-dielectric photonic materials. Herein, we present an analytical and numerical study on the strain-responsive spectral properties of a bioinspired sensor. The sensor structure contains a two-dimensional periodic array of dielectric nanodisks to mimic the optical behavior of grana lamellae inside chloroplasts. To accumulate a noticeable response, we exploit the collective optical mode in grana ensemble. In higher plants, such a mode appears as Wood's anomaly near the chlorophyll absorption line to control the photosynthesis rate. The resonance is shown persistent against moderate biological disorder and deformation. Under the stretching or compression of a symmetric structure, the mode splits into a couple of polarized modes. The frequency difference is accurately detected. It depends on the stretch coefficient almost linearly providing easy calibration of the strain-sensing device. The sensitivity of the considered structure remains at 5 nm/% in a wide range of strain. The influence of the stretching coefficient on the length of the reciprocal lattice vectors, as well as on the angle between them, is taken into account. This adaptive phenomenon is suggested for sensing applications in biomimetic optical nanomaterials.

The kinetics and mechanism of interconversion within a system of [Fe2L3]4+ helicates and [Fe4L6]8+ cages.

Nature builds simple molecules into highly complex assemblies, which are involved in all fundamental processes of life. Some of the most intriguing biological assemblies are those that can be precisely reconfigured to achieve different functions using the same building blocks. Understanding the reconfiguration of synthetic self-assembled systems will allow us to better understand the complexity of proteins and design useful artificial chemical systems. Here we have prepared a relatively simple system in which two distinct self-assembled structures, a [Fe2L3]4+ helicate and a [Fe4L6]8+ cage that are formed from the same precursors, coexist at equilibrium. We have measured the rates of interconversion of these two species and propose a mechanism for the transformation.

Critical coupling vortex with grating-induced high Q-factor optical Tamm states.

We investigate optical Tamm states supported by a dielectric grating placed on top of a distributed Bragg reflector. It is found that under certain conditions the Tamm state may become a bound state in the continuum. The bound state, in its turn, induces the effect of critical coupling with the reflectance amplitude reaching an exact zero. We demonstrate that the critical coupling point is located in the core of a vortex of the reflection amplitude gradient in the space of the wavelength and angle of incidence. The emergence of the vortex is explained by the coupled mode theory.

Model of a tunable hybrid Tamm mode-liquid crystal device.

A concept of an easily tunable device based on hybrid Tamm modes is proposed. The device can be controlled using a high-sensitivity chiral liquid crystal serving as a mirror. The coupling of the chiral optical Tamm state with the Tamm plasmons is predicted. The Tamm plasmons are excited at different frequencies for the orthogonal linear polarizations, while the chiral Tamm state is excited at only one frequency. The properties of the proposed model are analytically and numerically calculated. The possibility of creating a two- and three-mode laser with tunable characteristics on the basis of the proposed model is discussed.

Chiral Optical Tamm States at the Interface between a Dye-Doped Cholesteric Liquid Crystal and an Anisotropic Mirror.

The resonant splitting of optical Tamm state numerically is demonstrated. The Tamm state is localized at the interface between a resonant chiral medium and a polarization-preserving anisotropic mirror. The chiral medium is considered as a cholesteric liquid crystal doped with resonant dye molecules. The article shows that the splitting occurs when dye resonance frequency coincides with the frequency of the Tamm state. In this case the reflectance, transmittance, and absorptance spectra show two distinct Tamm modes. For both modes, the field localization is at the interface between the media. The external field control of configurable optical and structural parameters paves the way for use in tunable chiral microlaser.

Electrically induced transformations of defects in cholesteric layer with tangential-conical boundary conditions.

Electric-field-induced changes of the orientational structures of cholesteric liquid crystal layer with the tangential-conical boundary conditions have been investigated. The samples with the ratio of the cholesteric layer thickness d to the helix pitch p equalled to 0.57 have been considered. The perpendicularly applied electric field causes a decrease of the azimuthal director angle at the substrate with the conical surface anchoring. In the cells with d = 22 µm, the defect loops having the under-twisted and over-twisted areas are formed. At the defect loop the pair of point peculiarities is observed where the 180° jump of azimuthal angle of the director occurs. Under the action of electric field the loops shrink and disappear. In the cells with d = 13 µm, the over-twisted and under-twisted defect lines are formed. Applied voltage results in the shortening of lines or/and their transformation into a defect of the third type. The director field distribution near defect lines of three types has been investigated by the polarising microscopy techniques. It has been revealed that the length ratio between the over-twisted and third-type defect lines can be controlled by the electric field.

Transanal total mesorectal excision for rectal cancer has been suspended in Norway.

BACKGROUND: Transanal total mesorectal excision (TaTME) for rectal cancer has emerged as an alternative to the traditional abdominal approach. However, concerns have been raised about local recurrence. The aim of this study was to evaluate local recurrence after TaTME. Secondary aims included postoperative mortality, anastomotic leak and stoma rates. METHODS: Data on all patients who underwent TaTME were recorded and compared with those from national cohorts in the Norwegian Colorectal Cancer Registry (NCCR) and the Norwegian Registry for Gastrointestinal Surgery (NoRGast). Kaplan-Meier estimates were used to compare local recurrence. RESULTS: In Norway, 157 patients underwent TaTME for rectal cancer between October 2014 and October 2018. Three of seven hospitals abandoned TaTME after a total of five procedures. The local recurrence rate was 12 of 157 (7·6 per cent); eight local recurrences were multifocal or extensive. The estimated local recurrence rate at 2·4 years was 11·6 (95 per cent c.i. 6·6 to 19·9) per cent after TaTME compared with 2·4 (1·4 to 4·3) per cent in the NCCR (P < 0·001). The adjusted hazard ratio was 6·71 (95 per cent c.i. 2·94 to 15·32). Anastomotic leaks resulting in reoperation occurred in 8·4 per cent of patients in the TaTME cohort compared with 4·5 per cent in NoRGast (P = 0·047). Fifty-six patients (35·7 per cent) had a stoma at latest follow-up; 39 (24·8 per cent) were permanent. CONCLUSION: Anastomotic leak rates after TaTME were higher than national rates; local recurrence rates and growth patterns were unfavourable.

ANTECEDENTES: La resección total del mesorrecto transanal (transanal total mesorectal excision, TaTME) para el cáncer de recto se ha propuesto como una alternativa al abordaje abdominal tradicional. Sin embargo, la recidiva local (local recurrence, LR) después de este procedimiento es motivo de preocupación. El objetivo de este estudio fue evaluar la LR en pacientes operados mediante TaTME. Los objetivos secundarios incluyeron la mortalidad postoperatoria, las fugas anastomóticas y el porcentaje de estomas. MÉTODOS: Se registraron los datos de todos los pacientes operados mediante TaTME y se compararon con las cohortes nacionales del Registro Noruego de Cáncer Colorrectal (Norwegian Colorectal Cancer Registry, NCCR) y del Registro Noruego de Cirugía Gastrointestinal (Norwegian Registry for Gastrointestinal Surgery, NoRGast) utilizando estimaciones de Kaplan-Meier y la prueba de log-rank para comparar curvas de LR. RESULTADOS: En Noruega, 157 pacientes se sometieron a TaTME por cáncer de recto entre octubre de 2014 y octubre de 2018. Tres de siete hospitales abandonaron el TaTME después de un total de cinco procedimientos. La LR observada fue 12/157 (7,6%), siendo ocho de ellas multifocales o extensas. La tasa estimada de LR a 2,4 años fue de 11,6 % (i.c. del 95% 6,6 a 19,9) versus 2,4 % (1,4 a 4,3) en el NCCR (log rank P < 0,001). El cociente de riesgos instantáneos (hazard ratio, HR) ajustado fue 6,7 (i.c. del 95% 2,9 a 15,3). Las fugas anastomóticas que precisaron una reintervención después de TaTME ocurrieron en un 8,4% versus 4,5% en el registro NoRGast (P = 0,047). Cincuenta y seis pacientes (35,7%) tenían un estoma en el último seguimiento; 39 (24,8%) eran permanentes. CONCLUSIÓN: Las tasas de fuga anastomótica tras una TaTME fueron más altas que los datos nacionales con tasas de LR y patrones de crecimiento desfavorables.