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

Effects of substituents in polyvinylcarbazole structures on their optical properties

Absorption, photoluminescence, and photoluminescence excitation spectra of solutions and thin films of N-vinylcarbazole polymers and copolymers with various substituents directly on the carbazole moiety and on the polymer chain were studied comprehensively. Polymers that were used previously to develop polymer composites with polymethine dyes having photosensitivity over a broad spectral range including the visible and near-IR regions were selected for the studies

An experimental and theoretical study of exciplex-forming compounds containing trifluorobiphenyl and 3,6-di-tert-butylcarbazole units and their performances in OLEDs

Derivatives of trifluorobiphenyl and 3,6-di-tert-butylcarbazole were synthesised as potential components of emitting layers of OLEDs. Molecular design of the compounds was performed taking into consideration the hydrogen bonding ability of the fluorine atom and electron-donating ability of the carbazole moiety. Their toluene solutions exhibited very high triplet-energy values of 3.03 eV and 3.06 eV. Ionisation energies of the compounds in the solid-state were found to be in the range from 5.98 to 6.17 eV. Density functional theory (DFT) calculations using the ωB97XD functional, with the ω parameter tuned in the presence of the solvent, uncovered singlet–triplet energy splitting in good agreement with the experimental results. The materials were tested in the emissive layers of OLEDs, showing the ability to form exciplexes with complementary electron-accepting 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine. Using the synthesised compounds as exciplex-forming materials, highly efficient exciplex emission-based OLEDs were developed. In the best case, a high maximum current efficiency of 24.8 cd A−1, and power and external quantum efficiencies of 12.2 lm W−1 and 7.8%, respectively, were achieved

The Effect of Park and Urban Environments on Coronary Artery Disease Patients: A Randomized Trial

© 2015 Regina Grazuleviciene et al. Aim. To test the hypothesis that walking in a park has a greater positive effect on coronary artery disease (CAD) patients' hemodynamic parameters than walking in an urban environment. Methods. Twenty stable CAD patients were randomized into two groups: 30-minute walk on 7 consecutive days in either a city park or busy urban street. Wilcoxon signed-rank test was employed to study short-term (30 min) and cumulative changes (following 7 consecutive days of exposure) in resting hemodynamic parameters in different environments. Results. There were no statistically significant differences in the baseline and peak exercise systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), exercise duration, or HR recovery in urban versus park exposure groups. Seven days of walking slightly improved all hemodynamic parameters in both groups. Compared to baseline, the city park group exhibited statistically significantly greater reductions in HR and DBP and increases in exercise duration and HR recovery. The SBP and DBP changes in the urban exposed group were lower than in the park exposed group. Conclusions. Walking in a park had a greater positive effect on CAD patients' cardiac function than walking in an urban environment, suggesting that rehabilitation through walking in green environments after coronary events should be encouraged

Electrochemical cross-linking of carbazole derivatives: a new route for bulk heterojunction based on semi-interpenetrating polymer networks

Electrochemical behaviors of different pendant carbazole based oligomers have been studied for the realization of electroactive tridimensional structures. 3-substitution by hydrazone functional groups onto the pendant carbazole moieties increases the electron donor properties of the electroactive units. Electrochemical oxidation of thin films of the oligomer precursors deposited onto electrode ensures the formation of a cross-linked structure by in situ anodic coupling with the formation of biscarbazole redox sites. When the electrochemical cross-linking of the oligomers is realized in the presence of the electron acceptor polyimide (perylene based), we form a semi-interpenetrating polymer network (semi-IPN) coated as a thin layer. The electrochemical behavior of the semi-IPN shows two reversible oxidations and two reversible reduction peaks indicating respectively the p-doping of the biscarbazole entity and the n-doping of the perylene one. The presence of hydrazone substituents modifies the electron donor properties of the semi-IPN and should influence the electron transfer properties from biscarbazole to perylene units in bulk heterojunction solar cells

An iminodibenzyl–quinoxaline–iminodibenzyl scaffold as a mechanochromic and dual emitter: donor and bridge effects on optical properties

The influence of phenyl linkage and donor strength on the photophysical properties of new derivatives of quinoxaline-containing iminodibenzyl and iminostilbene moieties is studied. The donor–acceptor derivatives showed dual thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) despite a large energy gap between the excited singlet and triplet states (ca. 0.5 eV). This extremely rare observation is explained by the twisted and rigidified structure of the iminodibenzyl moiety

Carbazole based polymers as hosts for blue iridium emitters: synthesis, photophysics and high efficiency PLEDs

This article reports the synthesis of new carbazole based polymers and their application as hosts in sky-blue polymer light emitting devices (PLEDs) with a solution-processed emitting layer doped with a cyclometalated Ir(III) complex. We systematically investigate their effect on the PLED performance. A current efficiency of 19.7 cd A(-1) and a brightness of 1850 cd m(-2) were achieved with these polymers. The roll-off in electrophosphorescent quantum efficiency in PLEDs was shown to arise mainly from triplet-triplet annihilation between dopants in the hosts with tert-butyl groups. It has been shown that in the devices with hosts without tert-butyl groups the efficiency roll-off is additionally affected by electric field quenching. In these carbazole based polymers, triplet dimers are formed and tert-butyl groups do not limit the intermolecular interactions to prevent triplet dimer formation, nevertheless tert-butyl groups reduce charge transport