An ambipolar BODIPY derivative for a white exciplex OLED and cholesteric liquid crystal laser toward multifunctional devices

A new interface engineering method is demonstrated for the preparation of an efficient white organic light-emitting diode (WOLED) by embedding an ultrathin layer of the novel ambipolar red emissive compound 4,4-difluoro-2,6-di(4-hexylthiopen-2-yl)-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (bThBODIPY) in the exciplex formation region. The compound shows a hole and electron mobility of 3.3 × 10–4 and 2 × 10–4 cm2 V–1 s–1, respectively, at electric fields higher than 5.3 × 105 V cm–1. The resulting WOLED exhibited a maximum luminance of 6579 cd m–2 with CIE 1931 color coordinates (0.39; 0.35). The bThBODIPY dye is also demonstrated to be an effective laser dye for a cholesteric liquid crystal (ChLC) laser. New construction of the ChLC laser, by which a flat capillary with an optically isotropic dye solution is sandwiched between two dye-free ChLC cells, provides photonic lasing at a wavelength well matched with that of a dye-doped planar ChLC cell

Three-terminal light-emitting device with adjustable emission color

A three-terminal organic light-emitting device with a periodic interrupted middle electrode is developed to allow for an adjustable emission color. The emission results from three independent light-emitting diodes with one diode utilizing exciplex emission. An equivalent electrical circuit is suggested taking the current–voltage characteristics and the direction of current flow through the organic structure into account. Two diodes are formed between the embedded middle electrode and the LiF/Al top and ITO bottom electrode, respectively, and the third diode utilizes that part of the device without the middle-electrode exhibiting exciplex emission. It will be shown that the spectrum of the emitted light can be tuned from blue to orange by controlling the applied potentials to the device terminals

Star-Shaped Carbazole Derivatives for Bilayer White Organic Light-Emitting Diodes Combining Emission from Both Excitons and Exciplexes

Star-shaped carbazole-based compounds were synthesized by the Buchwald–Hartvig method. The materials were examined by various experimental and theoretical methods, including differential scanning calorimetry, UV spectrometry, electron photoemission, time-of-flight techniques, and DFT (B3LYP) calculations. The synthesized compounds showed high thermal stability with the initial weight loss temperature higher than 400 °C. The electron photoemission spectra of the layers of the amorphous materials showed ionization potentials of 4.9 eV. Tri­(9-hexylcarbazol-3-yl)­amine showed high hole mobility (μ = 10^–3 cm² V^–1 s^–1 at an electric field of 3.6 × 10⁵ V/cm). The star-shaped compounds were used for the preparation of bilayer white organic light-emitting diodes which combine emission from both excitons and exciplexes. The brightness of the white organic light emitting diode at 7 V is 300 cd/m² with current efficiency 2.3 cd/A and CIE coordinates (0.37, 0.35) which are very close to the equienergy white point (0.33, 0.33)

Nine-ring angular fused biscarbazoloanthracene displaying a solid state based excimer emission suitable for OLED application

A new biscarbazoloanthracene consisting of nine fused aromatic rings, including two pyrrole units, has been obtained in a straightforward and convergent synthesis. Computational chemistry and conformational analysis revealed that the semiconductor’s molecule is not planar, the two carbazole moieties being helical twisted from the plane of the anthracene unit. Photophysical and electrochemical measurements showed that this angular fused heteroacene has a low lying HOMO energy level with a wide band gap despite its extended p-conjugated molecular framework. Based on its relatively low-lying HOMO level, the semiconductor promises a high environmental stability in comparison to other related linear fused acenes and heteroacenes. The biscarbazoloanthracene has been applied as the light emitting layer in a white light emitting diode (WOLED). It is proposed that the white OLED feature is due to dual light emission properties from the active semiconductor layer being based on both the molecular luminescence of the small molecule and a discrete excimer emission made possible by suitable aggregates in the solid state. Noteworthy, this is the first reported example of such a behavior observed in a small molecule heteroacene rather than an oligomer or a polymer

Highly Efficient Blue Organic Light-Emitting Diodes Based on Intermolecular Triplet–Singlet Energy Transfer

Diphenilamino-substituted carbazoles were used as guest compounds for the preparation of highly efficient blue organic light-emitting diodes based on the phenomenon of delayed fluorescence. It was shown that the spectra of the delayed fluorescence of host–guest systems are identical to those of the prompt fluorescence and in general coincide with the photoluminescence spectra of the guest films. The congruence of the prompt and delayed fluorescence spectra is explained by the effective intermolecular triplet–singlet (T → S) energy transfer from the excited T states of the host to the S states of the guest molecules. High external electroluminescence efficiency of the fabricated electroluminescent devices, reaching 17%, is comparable to that achieved in phosphorescence-based organic light-emitting diodes

The choice of legal form of business from the point of view of tax burden

The aim of this thesis is to assess the possibilities of tax optimization in relation to the different legal forms of business. The thesis describes the various legal forms of business and tax system according to the valid legislation of the Czech Republic. The next step is analyze tax burden on individual forms, especially in terms of income tax. The methodology of thesis includes a procedure for determining of the tax burden, actually the tax obligations and available resources. A substantial part of the thesis are tax optimization options and their impact on tax obligation. The practical part of thesis deals with some forms of business and compares their tax burden and the available resources that are available after the payment of compulsory payments. The conclusion of thesis contains a summary and comparison of results from the practical part, the advantages and disadvantages of forms and recommendations. This recommendation should provide guidance to future businessmen when choosing a legal form of business if they are making a decisions on the basis of the above mentioned two aspects, namely the tax burden and the resources available after payment of compulsory payments