Tuning the Thermal Relaxation of a Photochromic Dye in Functionalized Mesoporous Silica

Abstract

In this study, it is shown that the kinetics of the back‐switching reaction of a photochromic spirooxazine dye encapsulated in mesoporous silica materials can be significantly influenced both by the space available to the dye molecules and by the functionalization of the silica wall. Steric hindrance of the ring‐closing process due to high dye content or small pore size leads to a slow fading speed of the irradiated dye species. Further, the density of surface silanol‐groups present at the silica walls has an effect on the switching behavior of the dye because of their ability to stabilize the zwitterionic merocyanine isomers, thereby slowing the fading process from the open to the closed form. This stabilization effect is further enhanced in the presence of acidic functional groups, while, in contrast, basic functional groups reduce the stabilization of the open‐from dye isomers, and thus a faster decay of the irradiated species is observed. Control over the fading speed of photochromic dyes is interesting for applications requiring a particularly fast or slow fading speed.

Facile preparation of stable palygorskite/methyl violet@SiO2 “Maya Violet” pigment

“…So, the hydrolytic condensation of TEOS on the surface of the PAL/MV pigment was carried out under the existence of CTAB with ammonia as the catalyst according to a previously reported method [26]. CTAB is frequently used as structuring agent to form mesoporous structures [29,40,41]. According to the UV-Vis spectra and images of the supernatants after attack of 0.1 M HCl, the stability of PAL/MV@SiO 2 increases with increasing the dosage of CTAB.…”

“…In view of inertness, excellent stability, non-toxicity and optical transparency, silica coating has found extensive applications in optical, magnetic, catalytic and biochemical fields. Recently, preparation of inorganic and/or organic nanomaterials encapsulated by silica has turned into a research focus in material science [26][27][28][29]. The PAL/MV@SiO 2 pigments have uniform morphology and excellent stability against chemical attacks of acid, alkali and organic solvents.…”

Nanophotochromism

“…The study of photochromic transformation of 5- 4)oxazine] in functionalized mesoporous silica showed that the rate of thermal bleaching of the photoinduced merocyanine form decreased with increasing concentration of the photochromic compound and decreasing the pore size [84]. An increase in the density of surface silanol groups and the presence of acidic functional groups on the silica walls retard the thermal bleaching of the merocyanine form but basic functional groups reduce the stability of this form.…”

Control of optical properties through photochromism: a promising approach to photonics

“…As regards the coloration and fading processes, it is required to achieve a fast response in both directions to follow abrupt changes in the illumination conditions. Many studies have been published on the features of switching in polymer matrices, showing the effects of the free volume available for the isomerization that is related to the polymer properties (i. e. glass-transition temperature, T g ) and to chemical interaction between the dye and the matrix [50][51][52][53][54][55]. Moreover, the UV-triggered modulation of color is influenced by temperature that balances the effect of light by favoring the fading process.…”