The synthesis of red dyes based on diketo-pyrrolo-pyrrole chromophore to improve heat stability and solubility for color filter fabrication

Abstract To replace the conventional red pigment derived from diketo-pyrrolo-pyrrole by new red dyes prepared in this research, an acetylene linkage was introduced between N-alkyl diketo-pyrrolo-pyrrole and naphthalimidyl moiety. TGA analyses and solubility measurement were carried out to compare those of conventional red pigment, C.I. Pigment Red 254, which has been most popular as a red pixel of color filter. Most of the new red dyes were prepared starting from C.I. Pigment Red 254 by the sequent reactions, N-alkylation, Sonogashira coupling, hydrolysis and further Sonogashira coupling. Chemical structures of all red dyes were confirmed by 1H NMR and mass spectral analysis. TGA was carried out at 300 °C, and solubility measurement was carried out using by several organic solvents which can be used in the color filter fabrications. TGA indicated that the introduction of an acetylene linkage group into the N-alkyl diketo-pyrrolo-pyrrole ring combined by an N-butyl-naphthalimidyl system improved its heat stability. The result of weight reduction 1.4% at 300 °C can be identical to that of C.I. Pigment Red 254. The solubility of red dye prepared was observed around 5 g/L, therefore it can be used in the color filter fabrication process to eliminate the conventional photo-etching process.