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

Abstract

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 Rb(0.75)(NH(4))(5.25)[(Mo(3)O(8))(2)O(O(3)PC(CH(2)S(CH(3))(2))OPO(3))(2)]·8H(2)O (1) and a new material (Me(3)S)(4)[Mo(8)O(26)] (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 Mo(6+) cations associated with electron transfers from the sulfonium cations toward the POMs is proposed.

Organic–inorganic hybrid rare earth complexes based on polymolybdates with intrinsic photosensitive properties

“…One of the promising systems in this field are hybrid organic− inorganic materials based on polyoxomolybdates (POM's) and 35 organic cations (mainly organoammonium cations) [3][4][5][6][7]11] . To date, the photochromism mechanism of such materials has been investigated in detail.…”

“…To date, the photochromism mechanism of such materials has been investigated in detail. Namely, the physical process involved implies the photoreduction of Mo(Ⅵ) cations into Mo(Ⅴ) ones within the POM's block, with a concomitant displacement of a 40 labile hydrogen atom from the N + -H bond of the organic component to the mineral one [2][3][4]12]. Nevertheless, it must be underlined that the photogenerated hue of such hybrid materials depends on the chemical composition and the topology of the POM's, whatever the nature of the 45 associated organoammonium cations.…”

Addition of Metalated 3‐Alkyl‐Substituted Alkoxyallenes to Imines: Preparation of Tetrasubstituted 2,5‐Dihydropyrroles, Pyrrolidin‐3‐ones, and Pyrroles

“…As no hydrogen atoms could be located, it is not possible to determine N-H and H···O distances, nor N-H···O angles, for the observed hydrogen bonds, and so, only NH···O distances are reported. [11][12][13][14][15][16][17] Therefore, it is reasonable to consider that the intermolecular hydrogen bonding between the primary ammonium or glycinium countercations and the POM may contribute to the photochromism observed for the present compounds. For the glycine ligands that bridge the Y atoms, up to three types of intramolecular N-H···O hydrogen bonds to bridging oxo ligands are evident in all compounds (Figures S14 and S15), with NH···O distances in the range of 2.9-3.2 Å.…”

“…[1][2][3][4] Compounds based on polyoxometalates (POMs) of early transition metals, such as Mo or W, can be excellent candidates, due to their facile reduction and accompanying color changes. [11][12][13][14][15][16][17] Two mechanisms have been proposed, both of which involve UV-induced O→Mo/W ligand-to-metal charge-transfer (LMCT) transitions on the polyoxomolybdate or polyoxotungstate, affording a metastable charge-transfer state that contains Mo 5+ or W 5+ ions. [5][6][7][8] The conceptually simplest approach to photochromic POM-based compounds has been covalent grafting of organic photochromes, such as spiropyrans, to the POM framework, [9,10] which has not necessarily exploited the redox properties of the POM.…”

“…In this regard, Dessapt and co-workers reported a series of photochromic molybdobisphosphonate complexes with bisphosphonate ligands functionalized by various pendant alkylammonium or pyridinium groups, which exhibit efficient color change in the solid state, comparable with photochromic POMs with organoammonium cations. [14,15,20] Previously, we have reported several members of a family of hybrid amino acid mixed-metal POMs with interesting redox properties. These features are affected by the reducibility of the POM and the stability of the organic counterpart in the oxidized state, following formation of the charge-transfer complex, versus the tendency to bleach back to the ground state.…”