Effects of matrix and concentration on the photochromism of spirooxazine-doped polymeric films

One of the strategies to take advantage of the photoswitchable properties of spirooxazines, a well-known class of photochromic dyes [1,2], is represented by their encapsulation in transparent host matrices, like polymers [3], which may induce a variation of the optical properties and improve the performance of the material, thanks to a major protection from oxidative degradation [4]. Herein, we report a study of the modulation of the colourability and the colouring/bleaching rates in different polymeric matrices (Polymethylmetacrylate, PMMA, and expanded polystyrene, PS) of two spirooxazines: 1’,3’-dihydro-1’,3’,3’-trimethylspiro[2H-benz[a]anthra[3,4-b]-1,4-oxazine-2,2’-[2H]indole]-7,12-dione (SO1) and methyl-1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3′-[3H]naphth[2,1-b][1,4]oxazine]-9′-carboxylate (SO2). The influence of the photochromic concentration and the chemical nature of the polymeric matrix on the photophysical behaviour of the two molecules is investigated. The obtained results show how it is possible to design a multi-purpose photochromic system by simply varying its concentration within the polymeric matrix. Indeed, by the proper choice of the photochromic concentration, thin solid films showing great photoconversion efficiency, with fast change in transmittance, can be achieved under irradiation, together with the possibility to modulate the bleaching rate from few seconds to tens of minutes.