Heteroaromatic Binuclear Direct Dyes for Stable Keratin Coloration
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Solution Overview
Problem
Existing direct dyes for keratin fibers, such as human hair, suffer from temporary or semi-permanent coloration, poor wash-fastness, and light-sensitivity, leading to fading and instability, especially when exposed to perspiration and sunlight, and lack the ability to maintain dark shades without lightening the hair beforehand.
Innovation Solution
A novel heteroaromatic binuclear direct dye composition comprising a pyridine nucleus, specifically a compound of formula (I), which provides stable, light-fast, and resistant coloration, allowing for consistent dark to grey shades without changing color upon washing, light exposure, or sweating, and maintains the initial shade after multiple applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional direct dyes are used for keratin fibers, then the dyeing process is simple and quick, but the coloration is temporary or semi-permanent with poor wash-fastness and light sensitivity
Solution Approach 1:
The patent employs composite dye molecules containing multiple chromophoric systems (azo groups, pyridine nuclei, and heteroaromatic rings) combined with specific auxiliary groups. This composite structure creates synergistic effects where the multiple chromophores work together to provide both dark coloration and improved stability, resolving the contradiction between reliability and complexity by integrating multiple functional elements into a unified molecular architecture.
Solution Approach 2:
The invention modifies the chemical parameters of direct dyes by introducing specific heteroaromatic nuclei (pyridine, pyrimidine, triazine) and controlling the arrangement of chromophoric systems. These parameter changes in molecular structure fundamentally alter the dye's interaction with keratin fibers, transforming temporary coloration into stable, long-lasting coloration while maintaining the direct dye application simplicity.
2Reliability
If direct dyes are applied to achieve dark black shades, then the coloration is intense, but the dye fades over time due to light sensitivity and poor resistance to photochemical attack
Solution Approach 1:
The patent fundamentally changes the chemical parameters of the chromophore system by incorporating heteroaromatic nuclei (pyridine, pyrimidine, triazine) alongside traditional azo groups. This structural modification increases the chromophore's resistance to photochemical attack while maintaining its light-absorbing capability, thereby improving light-fastness without sacrificing the dark color intensity required for black shades.
3Reliability
If conventional direct dyes are used to dye hair without lightening, then the application process is simple, but the dye cannot achieve consistent dark shades and changes color after washing or light exposure
Solution Approach 1:
The invention modifies the chemical parameters of the dye molecules to enhance their affinity for keratin fibers and improve their stability under various conditions. The specific arrangement of chromophoric systems and auxiliary groups in the heteroaromatic binuclear direct dyes enables consistent dark shade deposition directly on unlightened hair, maintaining color consistency through washing and light exposure while preserving the simplicity of the application process.
4Reliability
If multiple applications of direct dyes are performed to maintain dark shades, then the color intensity is improved, but the shade changes towards blue, violet, red, green glints after fading
Solution Approach 1:
The patent uses composite dye molecules with multiple chromophoric systems (azo groups, pyridine nuclei, heteroaromatic rings) that work synergistically. This composite structure ensures that as the dye fades, all chromophores degrade uniformly, preventing the selective fading that causes shade shifts toward blue, violet, red, or green glints. The multi-chromophore system maintains shade stability throughout the color retention period.
Data Source
AI summary
Disclosed herein are novel heteroaromatic binuclear direct dyes, dye compositions containing these dyes and also a process for dyeing keratin fibers using them. In particular, the invention relates to heteroaromatic binuclear direct dyes comprising a pyridine nucleus.With these novel dyes, black shades that show good fastness can be obtained, and they also may show good stability in dye compositions.