Photochromism behavior prediction using statistical approach

Abstract

Photochromic compounds, namely spiropyran, spirooxazine, and naphthopyran have received much attention because of their high potential applications in various industrial fields. Since there are diverse applications of photochromic materials, there is a need to investigate and improve the photochromic performance with regard to stability. In this research, statistical approach was exploited to predict the behavior of these materials with focus on photostability. The photostability was investigated in three phases, which are solution, sol-gel matrix, and thin film. Minitab 16 was employed to generate the experimental designs and analyze the results. The effects of experimental errors, model assumptions, experimental designs, and modelling approaches on the results were discussed. Statistical models in predicting the photochromic behavior under study were developed and validated. For the first phase, the behavior of three photochromic dyes was observed in solution form. The types of dyes and solvents were screened using mixed-level factorial design to select which dye and solvent give the highest photostability. It was found that both type of dyes and solvents used as well as their interaction have significant effects on photostability, with spirooxazine as the most stable dye, followed by naphthopyran and spiropyran, and ethanol as the solvent. Since spirooxazine has the best photostability, its behavior was then studied in sol-gel matrix and film forms. In the second phase, central composite design was utilized to choose the optimal conditions for dye photostability in sol-gel matrix. It was discovered that the linear and squared terms of dye concentration, antioxidant concentration, and irradiation time have major influences on photostability of spirooxazine. The optimal level setting for sol-gel photostability value of -4.36615 was at 3.85 mM dye concentration, 0.069 % ppm antioxidant concentration, and 14.4 s irradiation time. These conditions were applied in sample preparation of spirooxazine matrix. For the last phase, dip coating process of photochromic film was optimized using central composite design. Both the linear and squared terms of withdrawal speed and dwell time affect photostability of spirooxazine film significantly. Thus, the best level setting for the film photostability value of -5.31852 was at 7.5 mm/s withdrawal speed and 123 s dwell time. The overall results revealed that photostability of spirooxazine was significantly improved in sol-gel matrix and film, as compared to solution form. As a conclusion, a better understanding of photochromic behavior has been achieved. Therefore, this work succeeds in predicting what levels of independent factors will lead to acceptable response values and tolerable variability.