The emission of circularly-polarized light is central to many applications, including data storage, quantum computation, biosensing, environmental monitoring and display technologies. An emerging method to induce (chiral) circularly-polarized (CP) electroluminescence from the active layer of polymer light emitting diodes (polymer OLEDs; PLEDs) involves blending achiral polymers with chiral small molecule additives, where the handedness/sign of the CP light is controlled by the absolute stereochemistry of the small molecule. Through the in-depth study of such a system we report an interesting chiroptical property: the ability to tune the sign of CP light as function of active layer thickness for a fixed enantiomer of the chiral additive. We demonstrate that it is possible to achieve both efficient (4.0 cd/A) and bright (8000 cd/m 2) CP-PLEDs, with high dissymmetry of emission of both left handed (LH) and right handed (RH) light, depending on thickness (thin films, 110 nm: g EL = 0.51, thick films, 160 nm: g EL = −1.05, with the terms "thick" and "thin" representing the upper and lower limits of the thickness regime studied), for the same additive enantiomer. We propose that this arises due to an interplay between localized CP emission originating from molecular chirality and CP light amplification or inversion through a chiral medium. We link morphological, spectroscopic, and electronic characterization in thin films and devices with theoretical studies in an effort to determine the factors that underpin these observations. Through the control of active layer thickness and device architecture, this study provides insights into the mechanisms that result in CP luminescence from CP-PLEDs, opportunities in CP photonic device design, and demonstrate high performance CP-PLEDs.

Circularly polarized (CP) electroluminescence has been demonstrated as a strategy to improve the performance of organic light emitting diode (OLED) displays. CP emission can be generated from both small molecule and polymer OLEDs (SM-OLEDs and PLEDs), but to date, these devices suffer from low dissymmetry factors (g-factor <0.1), poor device performance, or a combination of the two. Here, we demonstrate the first CP-PLED employing an inverted device architecture.

Polymer thin films that emit and absorb circularly polarised light have been demonstrated with the promise of achieving important technological advances; from efficient, high-performance displays, to 3D imaging and all-organic spintronic devices. However, the origin of the large chiroptical effects in such films has, until now, remained elusive. We investigate the emergence of such phenomena in achiral polymers blended with a chiral small-molecule additive (1-aza[6]helicene) and intrinsically chiral-sidechain polymers using a combination of spectroscopic methods and structural probes. We show that – under conditions relevant for device fabrication – the large chiroptical effects are caused by magneto-electric coupling (natural optical activity), not structural chirality as previously assumed, and may occur because of local order in a cylinder blue phase-type organisation. This disruptive mechanistic insight into chiral polymer thin films will offer new approaches towards chiroptical materials development after almost three decades of research in this area.

Abstract:Ultra high performance concretes (UHPCs) are cementitious composite materials with high level of performance characterized by high compressive strength, high tensile strength and superior durability, reached by low water-to-binder ratio, optimized aggregate size distribution, thermal activation, and fiber reinforcement. In the past couple of decades, more and more UHPCs have been developed and found their ways into practice. Thus, the demand for computational models capable of describing and predicting relevant aging phenomena to assist design and planning is increasing. This paper presents the early age experimental characterization as well as the results of subsequent simulations of a typical UHPC matrix. Performed and simulated tests include unconfined compression, splitting (Brazilian), and three-point-bending tests. The computational framework is formulated by coupling a hygro-thermo-chemical (HTC) theory and a comprehensive mesoscale discrete model with formulated aging functions. The HTC component allows taking into account various types of curing conditions with varying temperature and relative humidity and predicting the level of concrete aging. The mechanical component, the Lattice Discrete Particle Model (LDPM), permits the simulation of the failure behavior of concrete at the length scale of major heterogeneities. The aging functions relate the mesoscale LDPM mechanical properties in terms of aging degree, defined in this work as the ratio between the quasi-static elastic modulus at a certain age and its asymptotic value. The obtained results provide insights in both UHPC early age mechanisms and a computational model for the analysis of aging UHPC structures.

Detecting circularly polarized light (CPL) signals is the key technique in many advanced sensing technologies. Over the past decades, many efforts have been devoted to both the material design and...

Abstract:A significant step in space exploration during the 21st century will be human settlement on Mars.Instead of transporting all the construction materials from Earth to the red planet with incredibly high cost, using Martian soil to construct a site on Mars is a superior choice. Knowing that Mars has long been considered a "sulfur-rich planet", a new construction material composed of simulated Martian soil and molten sulfur is developed. In addition to the raw material availability for producing sulfur concrete and a strength reaching similar or higher levels of conventional cementitious concrete, fast curing, low temperature sustainability, acid and salt environment resistance, 100% recyclability are appealing superior characteristics of the developed Martian Concrete. In this study, different percentages of sulfur are investigated to obtain the optimal mixing proportions. Three point bending, unconfined compression and splitting tests were conducted to determine strength development, strength variability, and failure mechanisms. The test results show that the strength of Martian Concrete doubles that of sulfur concrete utilizing regular sand. It is also shown that the particle size distribution plays an important role in the mixture's final strength. Furthermore, since Martian soil is metal rich, sulfates and, potentially, polysulfates are also formed during high temperature mixing, which might contribute to the high strength. The optimal mix developed as Martian Concrete has an unconfined compressive strength of above 50 MPa. The formulated Martian Concrete is simulated by the Lattice Discrete Particle Model (LDPM), which exhibits excellent ability in modeling the material response under various loading conditions.

Chirality of organic molecules is characterized by selective absorption and emission of circularly-polarized light (CPL). A consensus for chiral emission (absorption) is that the molecular chirality determines the favored light handedness regardless of the light-emitting (incident) direction. Refreshing above textbook knowledge, we discover an unconventional CPL emission effect in organic light-emitting diodes (OLEDs), where counter-propagating CPLs exhibit opposite handedness. This direction-dependent CPL emission boosts the net polarization rate by orders of magnitude in OLED devices by resolving the long-lasting back-electrode reflection problem. The anomalous CPL emission originates in a ubiquitous topological electronic property in chiral materials, i.e., the orbital-momentum locking. Our work paves the way to design novel chiroptoelectronic devices and reveals that chiral materials, topological electrons, and CPL have intimate connections in the quantum regime.

Reactions of [H(4)L][PF(6)](4) with 4 equiv. of Mn(OAc)(2)·4H(2)O in the presence of air gave rise to a mononuclear Mn(III)-superoxo complex [Mn(III)L(O(2))(H(2)O)](PF(6))(2), which contains a bowl-shaped cationic structure with a D(4d) symmetry. It has an unprecedented linear end-on Mn(III)-O(2) unit and exhibited good efficiency and selectivity in the catalytic oxidation of alkenes with O(2) plus isobutyraldehyde under mild conditions.