Chun Yoon

Synthesis and characterization of thermally stable dyes with improved optical properties for dye-based LCD color filters

We have designed and synthesized six phthalocyanine dyes and one benzoperylene dye for dye-based green Liquid Crystal Display (LCD) color filters. The solubility, spectral properties and thermal stability of the prepared six phthalocyanine dyes varied depending on their isomeric structures and core metals. They were dissolved in industrial solvent–binder composites and spin coated with and without yellow compensating benzoperylene dye into dye-based LCD color filters. The prepared color filters exhibited superior optical properties compared to conventional pigment-based ones due to the fluorescence of benzoperylene dye and less light scattering resulting from the smaller particle size of the dyes. The phthalocyanine dyes substituted at the peripheral (β) positions showed enough thermal stability for color filters and the yellow benzoperylene dye effectively compensated the spectra for vivid green colors.

Improving the Contrast Ratio of Red Pixels in Liquid-Crystal Displays by Synthesizing Synergists from an Anthraquinone Colorant

The color properties of liquid-crystal displays are usually classified on the basis of color representations, contrast ratios, and brightness, which primarily depend on the properties of pigments. Among these classifications, the contrast ratio can be improved by minimizing the light scattering of the pigment particles, which is directly related to the degree of dispersion. Therefore, synergists are usually applied to increase the contrast ratio by augmenting the efficiency of the dispersion. In this study, synergists containing anthraquinone as a backbone were synthesized and then their performance in improving the contrast ratio was examined.

Synthesis and characteristics of metal-phthalocyanines tetra-substituted at non-peripheral (α) or peripheral (β) positions, and their applications in LCD color filters

Four metal-phthalocyanine dyes were synthesized to evaluate the variation of their properties with both the position of the substituents and the type of metal used for coordination. The substituent, ethyl 4-hydroxy-3-methoxybenzoate, was introduced at the non-peripheral (α) or the peripheral (β) position in order to improve the solubility of the phthalocyanine. Cu and Zn were chosen as coordination metals, both to increase thermal stability and to fine-tune the color of the complex. The resulting complexes were highly soluble in a range of organic solvents as well as industrial solvents, such as di(propylene glycol) methyl ether acetate, diethylene glycol monobutyl ether acetate, and propylene glycol methyl ether acetate. The solubility of the dyes substituted at the α-position was higher than that of β-substituted dyes. Structural analyses of the substituted phthalonitriles were achieved using 1H and 13C NMR spectroscopy, and high-resolution mass spectrometry. The structures of the dyes were confirmed by MALDI-TOF spectroscopy and FT-IR spectrophotometry. The optical properties and thermal stabilities of the dyes were estimated by UV–Vis spectrophotometry and thermogravimetric analysis. The synthesized dyes were cyan in color, and thus could be successfully applied in six-primary-color (RGBCMY) liquid crystal display (LCD) color filters in order to improve the color gamut. Dye-based color filters showing adequate optical spectra for LCD cyan color filters were manufactured. Appropriate compensating dyes were also required in order to cut off undesirable transmittance peaks.

Preparation of Thermally Stable Red Dyes Derived from Diketo-Pyrrolo-Pyrrole Pigment for LCD Color Filter

6 dyes derived from Diketo-pyrrolo-pyrrole pigment were prepared by introducing an N-alkyl group, an N-acyl group or an N-aryl group to the DPP-ring. Absorption maxima, thermal stability by a thermogravimetric analysis (TGA), and the chromatic characteristics of the fabricated films were measured. It was explained that the observed hypsochromic shift and the effects of N-substituent on thermal stability of the dyes as well as a chromaticity diagram.

The Synthesis and Characterizations of Thermally-Stable Yellow Metal Complex Dyes for LCD Color Filters

Eight kinds of yellow metal (III) complex azo dyes were synthesized using different diazo component, coupling component and metal ion. The effect on the thermal stability of the synthesized dyes by azo ligand with two different functional groups, alcohol and carboxylic acid, was studied. The characteristics of the synthesized dyes were examined by their absorption maxima, thermal stability by a thermogravimetric analysis (TGA), and the chromatic characteristics of the fabricated films were measured. It was also explained that the effect of functional groups on the thermal stability of the dyes as well as their chromaticity values.

Preparation of Red Dyes Derived from Quinacridone Pigment by Introducing N-substituent and Their Characteristics as a Colorant for LCD Color Filter

Six red dyes derived from quinacridone pigment (C. I. Pigment Red 122) were prepared by introducing an N-alkyl group or N-acyl group in the quinacridone ring. The characteristics of the synthesized dyes were examined by absorption maxima, solubility and thermogravimetric analysis (TGA). The introduction of N-alkyl group gave very little bathochromic shift of 2∼3 nm, whereas the presence of a withdrawing group at the nitrogen exhibited a large hypsochromic shift of 60∼45nm comparing to that of C. I. Pigment Red 122 which is unsubstitued at the nitrogen atom. In terms of weight reduction at 250°C, N-alkyl groups withstood to the thermal decomposition in comparison with the behavior of withdrawing groups at the position of nitrogen atom. The solubility of six dyes was dramatically increased by the introduction of N-substituent which clearly indicates their character as a dye rather than a pigment.