Organic light-emitting diodes (OLEDs) able to directly emit circularly polarized (CP) electroluminescence (CP-OLEDs) are rapidly gaining much interest, due to their possible applications in displays with antiglare filters and 3D displays. Development of more efficient CP-OLEDs can open their use also in point-of-care and personalized diagnostic tools, since CP light alteration can be related to health state of irradiated tissues. In this work it is shown that the performance of chiral europium complex-based CP-OLEDs can be improved both in terms of external quantum efficiency (measured on all the Eu bands) and degree of polarization of emitted photons (as measured by the dissymmetry factor gEL), by proper active layer formulation and through a fine tuning of the architecture of the device. Polarization performances (gEL = −1) are obtained about three times higher than for any other CP-OLED reported so far. Moreover, for the first time, it is shown that the position of the recombination zone (RZ) plays a major role on the polarization outcomes. In order to rationalize these results the level of light polarization is related to the position of the RZ allied with the reflection on the cathode through a simple mathematical model. The values predicted by this model are in qualitative agreement with the experimental ones

We describe the preparation of a compound whose molecules consist of two metal sandwich stands carrying tentacles with affinity to metal surfaces and holding an axle that carries a dipolar or a nonpolar rotator. The dipolar rotor exists as three pairs of enantiomers, rapidly interconverting at room temperature. When mounted on a gold surface, each molecule represents a chiral altitudinal rotor, with the rotator axle parallel to the surface. The surface-mounted rotor molecules are characterized by several spectroscopic and imaging techniques. At any one time, in about one-third of the dipolar rotors the rotator is free to turn and the direction of its dipole can be flipped by the electric field applied by an STM tip, as revealed by differential barrier height imaging. Molecular dynamics calculations suggest that electric field normal to the surface causes members of one pair of enantiomers to rotate unidirectionally.

This article provides insight into the interaction of synthetic conjugated polymers [polyfluorene derivatives (PFDs)] with layers of two-dimensional titanium carbide (Ti3C2T x ). Three derivatives with nonpolar, polar, and charged nitrogen-containing functionalities were synthesized via the Suzuki polycondensation reaction. The organic–inorganic PFD/Ti3C2T x hybrids were prepared and characterized using X-ray diffraction and a range of microscopic and spectroscopic techniques to elucidate the host–guest interaction mechanism. We show that polar polymers with charged nitrogen-containing ends have the strongest interaction with the Ti3C2T x layers, yielding an increase in interlayer spacing and large shifts in spectroscopic peaks. Furthermore, the effect of polymer backbone juxtaposition between Ti3C2T x layers on pseudocapacitance is discussed in detail. Our results suggest that new organic materials capable of intercalation between the layers of Ti3C2T x and other MXenes may be used in the design of hybrid structures for high-performance energy storage applications and beyond.

Colloidal nanoplatelets (NPLs), owing to their efficient and narrow-band luminescence, are considered as promising candidates for solution-processable light-emitting diodes (LEDs) with ultrahigh color purity. To date, however, the record efficiencies of NPL-LEDs are significantly lower than those of more-investigated devices based on spherical nanocrystals. This is particularly true for red-emitting NPL-LEDs, the best-reported external quantum efficiency (EQE) of which is limited to 0.63% (EQE = 5% for green NPL-LEDs). Here, we address this issue by introducing a charge-regulating layer of a polar and polyelectrolytic polymer specifically engineered with complementary trimethylammonium and phosphonate functionalities that provide high solubility in orthogonal polar media with respect to the NPL active layer, compatibility with the metal cathode, and the ability to control electron injection through the formation of a polarized interface under bias. Through this synergic approach, we achieve EQE = 5.73% at 658 nm (color saturation 98%) in completely solution processed LEDs. Remarkably, exposure to air increases the EQE to 8.39%, exceeding the best reports of red NPL-LEDs by over 1 order of magnitude and setting a new global record for quantum-dot LEDs of any color embedding solution-deposited organic interlayers. Considering the emission quantum yield of the NPLs (40 ± 5%), this value corresponds to a near-unity internal quantum efficiency. Notably, our devices show exceptional operational stability for over 5 h of continuous drive in air with no encapsulation, thus confirming the potential of NPLs for efficient, high-stability, saturated LEDs.

We observe polariton condensation in the yellow part of the visible spectrum from a planar organic semiconductor microcavity containing the molecular dye BODIPY-Br. We provide experimental fingerprint of polariton condensation under non-resonant optical excitation, including the non-linear dependence of the emission intensity and wavelength blueshift with increasing excitation density, single excitation pulse dispersion imaging and real space interferometry. The latter two allow us to visualise the collapse of the energy distribution and the long-range coherence of the polariton condensate.

Abstract:We have explored the optical properties of a series of strongly-coupled microcavities containing the fluorescent molecular dye BODIPY-Br (bromine-substituted boron-dipyrromethene) dispersed into a transparent dielectric matrix with each cavity having a different exciton-photon detuning. Using temperature dependent emission, time-resolved spectroscopy, white-light reflectivity and measurements of fluorescence quantum yield, we explore the population of polaritons along the lower polariton branch. We find that both the cavity fluorescence quantum efficiency and the distribution of polariton states along the lower polariton branch is a function of exciton-photon detuning. Importantly, we show that in the most negatively detuned cavities, the emission quantum efficiency approaches that of a control (non-cavity) film. We develop a simple fitting model based upon direct radiative pumping of polariton states along the LPB and use it to obtain an excellent agreement with measured photoluminescence as a function of temperature and excitonphoton detuning, and qualitative agreement with the measured photoluminescence quantum efficiency. The radiative pumping mechanism that we identify indicates that to facilitate the formation of a non-equilibrium polariton condensate in an organic-semiconductor microcavity, it is important to utilize materials having high fluorescent quantum efficiency and fast radiative rates.A semiconductor-microcavity is an optical structure that can be used to control interactions between light and matter [1] . A typical cavity structure is composed of two mirrors separated by a layer of semiconducting material having a thickness commensurate with the wavelength of light (~100 nm). Such structures confine the local electromagnetic field, and if the energy of the confined photon and excitonic transition are degenerate, interactions can occur in the strong-coupling regime [2][3][4][5] . Here exchange of energy between excitons and photons is faster than the photon damping or exciton-photon dephasing, with the eigenstates of the system being cavity polaritons (a coherent superposition between light and matter). Polaritons are observed through an anticrossing 3 around the resonant energy of the exciton and photon modes in optical reflectivity or photoluminescence (PL) emission measurements [6] . Polaritons are bosonic quasi-particles that exhibit properties of both their excitonic and photonic components, namely the ability undergo scattering through their matter component, to form a coherent polariton condensate [7] . The ability to create and manipulate such condensates offers significant opportunities to create low threshold lasers that operate without the need for a population inversion and devices for quantumsimulations [8][9][10][11] .Most studies of strong-coupling have been performed using cavities containing inorganic-based semiconductors such as GaAs [12] , CdTe [13] , ZnO [14] and GaN [15] , either using a bulk semiconductor layer or in more sophisticated quantum well-based structures ...

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Colloidal quantum dots (QDs) are emerging as true candidates for light-emitting diodes with ultrasaturated colors. Here, we combine CdSe/CdS dot-in-rod heterostructures and polar/polyelectrolytic conjugated polymers to demonstrate the first example of fully solution-based quantum dot light-emitting diodes (QD-LEDs) incorporating all-organic injection/transport layers with high brightness, very limited roll-off and external quantum efficiency as high as 6.1%, which is 20 times higher than the record QD-LEDs with all-solution-processed organic interlayers and exceeds by over 200% QD-LEDs embedding vacuum-deposited organic molecules.