Direct coloration of textiles with photochromic dyes. Part 2: The effect of solvents on the colour change of photochromic textiles

Polyester, acrylic and nylon textile substrates dyed with two spirooxazine dyes, 1,3,3-trimethyl-spiroindoline-2,3′-3H-naphth[2,1-b][1,4]oxazine (1a) and 6′-piperidino-1,3,3-trimethyl spiroindoline-2,3′-3H-naphth[2,1-b][1,4]oxazine (1b), exhibit significantly higher photochromic colour build-up when wet compared with after drying. A study of this phenomenon, extended beyond water to the influence of a series of selected organic solvents on photochromic behaviour, using colour measurement of the photochromic textiles under controlled ultraviolet irradiation conditions, is reported. The results of molecular modelling calculations (AM1 in water and PM5 in water) have been used as a means of interpreting the observed effects, in conjunction with qualitative arguments based on solvation and fibre swelling.