Tethering of modified Reichardt's dye on SBA-15 mesoporous silica: the effect of the linker flexibility

Solvatochromic Reichardt's dye has been covalently anchored to both aniline-functionalized and propylamine-functionalized SBA-15 mesoporous silicas. The former offers a rigid linker to the surface; the latter offers a flexible one. The optical properties of immobilized dye in the presence of various vapors and gases were investigated by means of in situ diffuse reflectance UV-visible spectroscopy. The nature of the linker (rigid or flexible), used to covalently immobilize the dye, was found to play a significant role in determining the solvatochromic response of the chromophore to molecules. The use of the rigid linker, which reduces dye-support secondary interactions, represents a significant improvement in view of sensing applications, due to the stronger effects of the interaction with molecules from the gas or vapor phase on the visible absorption spectrum. This study provides a direct observation of the effect of linker flexibility on the behavior of anchored species.