Sulfonium Polyoxometalates: A New Class of Solid-State Photochromic Hybrid Organic–Inorganic Materials

For the very first time, sulfonium polyoxometalate (POM)
assemblies are shown to develop efficient solid-state photochromism
in ambient conditions. The optical properties of the already known
Rb0.75(NH4)5.25[(Mo3O8)2O­(O3PC­(CH2S­(CH3)2)­OPO3)2]·8H2O
(1) and a new material (Me3S)4[Mo8O26] (2) under UV excitation are investigated
by diffuse reflectance spectroscopy, revealing that the color change
effect is highly tunable playing with the nature of the POM. A mechanism
involving the photoreduction of Mo6+ cations associated
with electron transfers from the sulfonium cations toward the POMs
is proposed.