Kyu Young Hwang

Showing their true colors? Full emission color tuning in the visible region can be achieved with salen-aluminum complexes that are electronically modulated at C5 of the phenoxide ring in the salen moiety. Emission spectra for various substituents R(5) are shown (EWG: electron-withdrawing group, EDG: electron-donating group).A series of salen-aluminum complexes, [{(R(5))(2)-salen(3-tBu)(2)}Al(OC(6)H(4)-p-C(6)H(5))] (salen=N,N'-bis(salicylidene)ethylenediamine; R(5)=H (1), tBu (2), Br (3), Ph (4),

The organic light-emitting diodes (OLEDs) employing complex [salen(tBu)4Al(OC6H4-p-C6H5)] (4) as a hole-blocking layer produced stable green EL emission of Ir(ppy)3 irrespective of changing current density and showed higher brightness and device efficiency than the BAlq-based device.

The excellent contrast ratio, visibility, and advantages in producing thin and light displays let organic light emitting diodes change the paradigm of the display industry. To improve future display technologies, higher electroluminescence efficiency is needed. Herein, the detailed study of the non-radiative decay mechanism employing density functional theory calculations is carried out and a simple, general strategy for the design of the ancillary ligand is formulated. It is shown that steric b

A discrete heterodinuclear Al (III)/Ir (III) complex shows bright-orange light emission when used as an active layer in host-dopant assembly organic light-emitting diodes based on a solution process.

The optical properties and the theoretical prediction of color optical shutter with dye-doped polymer network liquid crystal (PNLC) were investigated. The view-angle dependence of reflectance according to the bias conditions showed distinctive characteristics, which could be explained from the effects of dye absorption and path length. It was also shown that the thickness dependence of reflectance was strongly influenced by the light-scattering coefficient. Our experimental results matched up we

Abstract The light‐emitting dipole orientation (EDO) of a phosphorescent emitter is a key to improving the external quantum efficiency (EQE) of organic light‐emitting diodes (OLEDs) without structural modification of the device. Here, four homoleptic Ir complexes as a phosphorescent emitter are systematically designed based on the molecular structure of tris(2‐phenylpyridine)iridium(III) (Ir(ppy) 3 ) to control the EDO. Trimethylsilane, methyl, 2‐methylpropyl, and cyclopentylmethyl group substit

Abstract Förster resonance energy transfer (FRET) in sensitized fluorescent (SF) organic light‐emitting diodes (OLEDs) is an important process for suppressing triplet exciton loss during energy transfer toward the fluorescent dopant. Herein, the contribution of the relative orientation between the sensitizer and emitting dopant to the FRET in state‐of‐the‐art SF OLEDs is explained using experimental and theoretical approaches. The enhanced relative orientation factor ( κ 2 ) from 0.375 to 1.250

In this paper, multidirectional light-control reflective (LCR) films are developed in order to create an active reflective structure that will enhance the image brightness and contrast ratio of reflective dye-doped polymer-dispersed liquid crystal (D-PDLC) displays at lower viewing angles. Advantages of LCR films are that their production is low cost and they require a simple photolithographic fabrication method. The optimum design prism-type light-control reflective film succeeded in minimising

Treatment of AlMe 3 with 2 equiv of 2-(2 H -benzo[ d ][1,2,3]triazol-2-yl)-4,6-di- tert -pentylphenol ( Lig 1 H ) or 2- tert -butyl-6-(5-chloro-2 H -benzo[ d ][1,2,3] triazol-2-yl)-4-methylphenol ( Lig 2 H ) and subsequent addition of ROH afford monomeric and heteroleptic (OR)AlL 2 complexes [R = C 6 H 5, L = Lig 1, 1; R = p -C 6 H 4 Ph, L = Lig 1, 2; R = C 6 H 5, L = Lig 2, 3; R = p -C 6 H 4 Ph, L = Lig 2, 4 ]. The simple reaction between a quantitative amount of water and compound 1 gave the n

Abstract The enhancement of electro‐optical properties in reflective‐type dye polymer dispersed liquid crystal (PDLC) has been achieved by applying an additional white PDLC layer along with dye PDLC layer. This newly modified structure that consists of white PDLC layer and scattering reflector acts as an active reflector. In this practice, an additional arrangement of a polymer barrier layer is made‐up over white PDLC layer, to block the absorption of any solution from dye PDLC. The contrast rat

Determination of the formation of bright molecular fluorphores during the synthesis of pyrene-derived CNDs, through extensive separation and systematic characterization.

The color optical switching device by polymer network liquid crystal (PNLC) with color filter on a specular reflector shows excellent performance; white reflectance of 22%, color gamut of 32%, and contrast ratio up to 50:1 in reflective mode measurement. The view-angle dependence of the reflectance can be adjusted by changing the PNLC thickness. The color chromaticity shown by the device is close to the limit value of color filters, and its value nearly remains with respect to the operating volt

A color-reflective optical shutter structure has been studied using polymer-stabilized liquid crystal (PSLC) devices with a specular reflector. The combined effect of an LC, a polymer, a color dye, and a specular reflector results in a high performance of a reflective-mode optical shutter as well as of a simple structure with a fast response time capable of smooth moving images. The reflectance is up to 40%, one of highest for reflective devices, whose response times are fast enough to provide v