Abstract:

Objective With the increase of molecular weight, the chromatographic depth of dyes increases, but the solubility of dyes in supercritical carbon dioxide decreases. In order to design a dye molecular whose solubility and chromatographic depth meet the requirements, the above contradiction between solubility and chromatographic depth must be solved.

Method In this research, the two objective optimization problems about dye solubility and chromatographic depth were transformed into a single objective 0-1 programming problem. Among the problem, dye molecular solubility was regarded as the optimization objective function, and the chromatographic depth function was regarded as the constraint. In the program, the dye solubility was expressed by cohesive energy, and the model of cohesive energy and hydroxyl substitution position was established. The chromatographic depth of the dye was expressed by the maximum absorption spectral intensity in the visible light band. According to the geometric characteristics of the molecular structure of anthraquinone dyes, molecular symmetry was used as a heuristic rules to eliminate repeated substitution positions and reduce feasible paths, and the implicit number method was used to iteratively calculate the optimal substitution position of hydroxyl group.

Results The 5,7,12,14-pentaphentetra ketone molecule was taken as example for research. The cohesive energy and light absorption strength were calculated by the computer molecular dynamics simulation platform and relevant analysis software. Based on the above data, an optimization model was constructed, and the optimal molecular structure was obtained by solving the model. In order to determine whether the chromatographic depth of the optimal dye met the requirement, the UV absorption spectra about two molecular structures were compared. The light absorption intensity of the dyes substituted at positions 1, 4, and 6 was obviously higher than that of the dyes inserted with hydroxyl groups at other positions. Therefore, the chromatographic depth of the optimal dye met the requirement. Through molecular dynamics simulation of the optimal dye molecular structure and the actually produced Disperse Violet 26, the difference between the cohesive energies obtained from the two experiments was compared. It was seen that the designed optimal dye has greater cohesive energy and better solubility than Disperse Violet 26. The effectiveness of the design method was thus proved.

Conclusion With the increase of benzene rings in dye structure, more functional groups can be inserted into the molecular structure and it highlights the advantages of optimal design despite the longer reaction period. Symmetry is adopted to eliminate symmetrical positions, making the optimization calculation simpler. Another achievement from the research is the use of the implicit method to calculate the optimal number of functional groups and replacement positions at one time, which is more efficient than the combination optimization. Areas for improvement are also identified for future research. Firstly, plane symmetry is adopted to find symmetry points in this research, but the plane symmetry of anthraquinone dyes is directly related to many variables such as the intermolecular interaction, the state of molecular plane motion, cohesive energy and solubility. In order to improve the efficiency and accuracy of design, it is possible to establish the model of symmetry and state of molecular plane motion, the model of cohesive energy and solubility to design optimal dyes from molecular geometric structure. Secondly, the part of validation in this research is completed on the molecular dynamics platform. When solubility and chromatography are verified by actual dyeing experiments after the optimal dye is synthesized and manufactured, the conclusion of this research would be further proved.

Key words: anthraquinone type dye, hydroxyl group, solubility, implicit number method, molecular symmetry, optimal substitution, dye molecular design