The synthesis and characterisation of red dyes for colour filter fabrication

Pigment dispersion method is a mainstream method for liquid crystal displays (LCDs), yet their inherent light scattering by pigment particles often results in low transmittance. While dye have emerged as a promising alternative, their industrial adoption has been limited by poor photo-heat-stability. In this study, a series of six dyes were synthesised by introducing ester-functionalised alkyl chains of varying lengths into C.I. Pigment Red 254 by N-alkylation. The solubility of these dyes was tested, and their thermal stability and light absorption properties were investigated using TGA and UV-Vis. The results indicated that all dyes had solubility exceeding 5 wt% and ε greater than 104 L/(mol·cm). Notably, dyes 2 and 3 show exceptional thermal stability, with a weight loss of less than 5 wt% after by pre-baking at 230°C for 30 min. These dyes possess good solubility, strong light absorption, and high thermal stability, suggesting their suitability for colour filter applications. Additionally, colour filters were created by combining these dyes with pigments. Colour difference showed that ∆E of thermal stability and light stability were under 3. The colour filter incorporating dye 2 achieved a contrast ratio improvement ranging from 220–394.