Photochromic Properties of Polyoxotungstates with Grafted Spiropyran Molecules

Abstract

The first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA)₄­[PW₁₁O₃₉­{Sn­(C₆H₄I)}] precursor, two hybrid organic–inorganic species where a spiropyran derivative (SP) has been covalently grafted onto a {PW₁₁Sn} fragment via a Sonogashira coupling have been successfully obtained. Alternatively, a complex containing a silicotungstate {PW₁₁Si₂} unit connected to two spiropyran entities has been characterized. The purity of these species has been assessed using several techniques, including ¹H and ³¹P NMR spectroscopy, mass spectrometry, and electrochemical measurements. The optical properties of the hybrid materials have been investigated both in solution and in the solid state. These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic chromophore in solution. In contrast, these novel hybrid SP–POT materials display highly effective solid-state photochromism from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP–POT systems in the solid state strongly depend on the nature and the number of grafted SP groups