Abstract
The assembly of two distinct organic photochromic groups and polyoxometalate (POM) within a single molecule has been realized. In the hetero-functionalized Anderson polyanion MnMo6O18(SP)(SN), one spiropyran and one spironaphthoxazine cap the two faces of a planar {(MnMo6O18)-Mo-III-O-VI} fragment. A related symmetrical POM where the {(MnMo6O18)-Mo-III-O-VI} inorganic moiety is connected to two spironaphthoxazines has also been obtained, and isolated as an organoammonium (MnMo6O18(SN)(2)) or a cationic spiropyran ((SP)(3)MnMo6O18(SN)(2)) salt. The structures of MnMo6O18(SN)(2) and MnMo6O18(SP)(SN) have been solved by single-crystal X-ray diffraction analysis. In solution, both compounds exhibit electrochromic properties with multiple redox coloured states. The solid-state photochromism of all the compounds has also been extensively studied at room temperature. Contrary to the organic spironaphtoxazine derivative SNTris which is very poorly photochromic, the pale yellow colour of MnMo6(O18)(SN)(2) shifts to deep blue with high coloration contrast which underlines the positive effect of the grafting onto the inorganic platform. In addition, MnMo6O18(SN)(2) also shows good cyclability and exhibits a fast bleaching process. Finally, the temperature dependence of the solid-state photochromic properties of MnMo6O18(SN)(2) is also reported and compared to that of the related MnMo6O18(SP)(2). The photo-coloration process which is attenuated at low temperatures in both cases is clearly more affected for MnMo6O18(SN)(2). Moreover, the thermal fading process becomes significant at 340 K for MnMo6O18(SP)(2) and 260 K for MnMo6O18(SN)(2) underlining strong different optical behaviours between both materials.