Exciton-polaritons are bosonic quasiparticles that arise from the normal mode splitting of photons in a microcavity and excitons in a semiconductor material. One of the most intriguing extensions of such a light−matter interaction is the socalled ultrastrong coupling regime. It is achieved when the Rabi frequency (Ω R , the energy exchange rate between the emitter and the resonant photonic mode) reaches a considerable fraction of the emitter transition frequency, ω 0 . Here, we report a Rabi energy splitting (2ℏΩ R ) of 1.12 eV and record values of the coupling ratio (2Ω R /ω 0 ) up to 0.6-fold the material band gap in organic semiconductor microcavities and up to 0.5-fold in monolithic heterostructure organic light-emitting diodes working at room temperature. Furthermore, we show that with such a large coupling strength it is possible to undress the exciton homogeneous linewidth from its inhomogeneous broadening, which allows for an unprecedented narrow emission line (below the cavity finesse) for such organic LEDs. The latter can be exploited for the realization of novel monochromatic sources and near-IR organic emitting devices.

In the last few years, white-light emission from organic compounds has been the subject of increasing interest due to its potential impact on the lighting industry and backlight applications. In order to obtain white light from organic lightemitting devices (OLEDs), the simultaneous excitation of different molecular species emitting at different primary colors is required. [1,2] So far, the most exploited approach has been the fabrication of multilayer devices by consecutive evaporations or co-evaporation of different emitting compounds.[1±6]However, this technique requires complex technological processes and a large amount of wasted organic materials, resulting in relatively high fabrication costs. Spin-coating of a blend of different soluble emitters in a single layer seems to be a more cost-effective technique. [7,8] Though cheaper, this approach has the drawback that customized color combinations are not always possible due to Förster transfer from the highenergy emitting material (donor) to the low-energy one (acceptor), which induces emission only from the lower-gap compound. [9,10] An alternative approach which overcomes such a problem is to blend two blue-light-emitting organic molecules of different electron affinities, whose interaction gives rise to exciplex states. [11,12] The combination of the exciplex emission with the blue-light emission of the individual donor molecule results in the generation of white light. However, in both of these approaches the purity of the color emission is strongly dependent on the relative concentration of the different molecular species and, generally, on the applied voltage. This is a problem for lighting applications in which the source intensity (but not the color) has to be varied by changing the applied electrical power. [13] In this frame, the synthesis of a soluble compound showing white-light emission in the solid state is strongly desirable because it would enable the fabrication of a new class of devices which combine the simplicity and low cost of the single-layer spin-coated structures without the problems connected with the material concentration and bias.In this work, we demonstrate a bright single-layer white OLED realized by spin-coating a single emitting molecular material, namely 3,5-dimethyl-2,6-bis(dimesitylboryl)-dithieno[3,2-b:2¢,3¢-d]thiophene (compound 1 in Fig. 1). In 1, white electroluminescence is achieved by the superposition of the intrinsic blue±green-light emission (BGE) of the single molecule with a red-shifted emission (RSE) that occurs only in the solid state. The origin of the RSE peak is due to the formation of cross-like dimers between the molecules. This has been demonstrated by optical measurements and theoretical calculations, and also performed on similar compounds functionalized with different substitution patterns (2, 3, and 4 in Fig. 1) in order to control the self-assembling of the molecules. By virtue of the excellent properties of compound 1, namely the good electron-acceptor characteristics of the dimesitylboryl moieties...

We demonstrate a straightforward strategy to fabricate a multilayer inorganic/organic polarized light-emitting diode device based on highly ordered arrays of rod-shaped nanocrystals as the active species. We have developed a simple and effective method that allows colloidal CdSe/CdS core/shell nanorods to be laterally aligned in smectic or nematic phases on the surface of water. A floating film of such ordered nanorods has been collected by a poly(dimethylsiloxane) (PDMS) stamp pad and transferred by contact printing onto previously evaporated organic layers. Thanks to the lateral nanorod alignment the as-prepared film exhibited strong polarized photoluminescence and it has been used as emissive layer in the polarized electroluminescent device.

Incubating in the rise of perovskite photovoltaic era, the advances in material design encourage further promising optoelectronic exploitations. Here, we evaluate halide perovskite envisioning light-emitting applications, with a particular focus to the role that this material can effectively play in the field, discussing advantages and limitations with respect to state of art competing players. Specific benefits derive from the use of low dimensional and nanostructured perovskites, marginally exploited in photovoltaic devices, allowing for a tuning of the excited states properties and for the obtainment of intrinsic resonating structures. Thanks to these unique properties, halide perovskite ensure a great potential for the development of high-power applications, such as lighting and lasing.