Fast decoloration of spironaphthooxazine bound to a poly(dimethylsiloxane) network

Abstract

Spironaphthooxazine (SNO) was attached to a three-dimensional network of polysiloxane through the allyloxy group on C-7 of the naphthalene ring of SNO, and the photochemical coloration and thermal decoloration behaviors of this material (Film-P) were examined by comparing their properties with those of model SNO having a 7-propyloxynaphthyl group in solution, in a doped polysiloxane film (Film-D), and in a doped PMMA film. For Film-P, the SNO units were connected to a part of the vinyl groups on the Si atoms of a linear polysiloxane by hydrosilylation, and the remaining vinyl groups were bridged by the bifunctional linear polysiloxane possessing two hydrosilyl groups at both ends of the chain. While Film-P containing 1.7 x 10(-3) mol dm(-3) of the SNO unit formed a transparent film, Film-D containing more than 1.2 x 10(-3) mol dm(-3) could not form a transparent film but segregation of SNO occurred. A transparent Film-D was prepared at 0.54 x 10(-3) mol dm(-3) SNO concentration. The decoloration reaction rate of Film-D was faster than those for Film-P, solutions, and PMMA. However, due to the low concentration, the coloration of Film-D was weak. When the concentration of SNO in Film-P was increased 5.7 times, the decoloration rate became 3.6 times faster. Its half-life time was 0.9 s, which is 3.1 times as fast as that of corresponding solution in hexamethyldisiloxane.

Efficient coloration and decoloration reactions of fast photochromic 3H–naphthopyrans in PMMA-b-PBA block copolymer

“…When the large structural change is induced by the photochromic reaction, the thermal back reaction rate crucially depends on the viscosity of the polymer matrix [10,[19][20][21]. The ΔV ‡ is one of the effective measure to elucidate the structural change associated with chemical reactions because ΔV ‡ originates from the difference in the partial molar volumes between the initial state and the transition state.…”

“…We previously demonstrated that the value of the activation free volume (ΔV ‡ ) for the thermal back reaction is an effective measure to evaluate the efficiency of the photochromic reaction in polymer matrix [17,18]. The other solution is to reduce the viscosity of a host polymer matrix [10,[19][20][21]. By using the soft polymer matrix such as siloxane or using the plasticizer, the glass transition temperature (Tg) of a polymer matrix is reduced effectively for the use of the host polymer matrix of photochromic molecules [10].…”

Highly transparent photochromic films with a tunable and fast solution-like response

“…The second strategy is to facilitate the dye isomerization by providing softer (less steric hindrance) or void (free-volume) matrix environments. This has been accomplished by i) functionalizing the photochromic molecules with flexible tails, [46][47][48][49][50] ii) embedding the dyes in different media such as low glass transition and/or plasticized polymers, 51,52 hybrid organic/inorganic materials, [53][54][55] hydrogels, 56 or organogels, 57 and iii) encapsulating the molecules in the cages of hybrid mesostructured (nano)materials, [58][59][60][61][62] metal-organic frameworks, 63,64 and supramolecular assemblies. [65][66][67] The encapsulation was also explored by our group, which reported tunable photochromic properties (fast or reverse photochromism) in solid materials by embedding core-shell capsules into polymeric films, 20,68,69 a strategy that was also successfully extended to the fabrication of liquid-like thermochromic 70 and white-emitting 71 materials.…”

Phototriggered micromanufacturing using photoresponsive amorphous spirooxazine films

“…50 It is well known that the thermal decoloration reaction rate decreases when SOs are placed in solid matrices such as polymer films. 51,52 Prolonged half-lives observed for SO2-SO5 are thought to be ascribed to their relatively large volume for isomerization. They may also be ascribed to their increased T g s since the decoloration experiments were performed at room temperature (300-306 K).…”