Application of Photochromic Spiroindolinonaphthoxazines in Disperse Dyeing of Polyester: Re-evaluating Process Optimization by Analyzing Degradation Behavior and Photochromic Properties

In recent years, there has been a growing interest in smart textiles, and photochromic compounds are well-established colorants in the manufacturing of UV-sensing smart textiles. This study investigated the optimal dyeing conditions for photochromic spiroindolinonaphthoxazines dyes, specifically trimethylspiroindoline-2,3′-3H-naphth[2,1-b][1,4]oxazine (SNO) and 9′-hydroxy-1,3,3-trimethylspiro{indoline-2,3′[3H]naphtho[2,1-b][1,4]oxazine} (SNO–OH), on polyester fabric using an aqueous exhaust dyeing method. The results revealed that the optimal conditions for dyeing polyester fabric with spiroindolinonaphthoxazines dyes are pH 8, 100 °C, and 20 min. Liquid chromatography–mass spectrometry analysis demonstrated the susceptibility of these dyes to degradation at higher dyeing temperatures and acidic pH. Notably, the singlet oxygen quencher 1,4-diazabicyclo[2,2,2] octane enhanced photochromic performance by protecting the dyes from degradation during the dyeing process. Polyester fabrics dyed with SNO exhibited superior photochromic behavior compared to those dyed with SNO–OH, including higher color build-up, exhaustion, fatigue resistance, and color fastness properties. Overall, the optimization of the dyeing conditions and the use of a singlet oxygen quencher are crucial for achieving optimal photochromic performance and dye stability on polyester fabrics.