Photochromic Properties of Polyoxotungstates with Grafted Spiropyran Molecules

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.