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 23nm, whereas the presence of a withdrawing group at the nitrogen exhibited a large hypsochromic shift of 6045nm comparing to that of C. I. Pigment Red 122 which is unsubstitued at the nitrogen atom. In terms of weight reduction at 250C, 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.