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Photochromic hybrid polyoxometalates

Hélène Serier-Brault (Associate Professor), Rémi Dessapt (Associate Professor)

We design new solid-state photochromic materials that exhibit reversible light-induced color changes. These systems are of great interest in a wide range of marketable applications (pigments for paints and windows, cosmetics, UV sensors), and other promising technological applications in photonic (optical switches, 3D high-density optical data storage). Our materials are built upon POMs associated with a wide range of organic molecules. They develop remarkable photoinduced optical properties in the solid state that associate the generation of excitons into the POM with electron transfers – and sometimes atom displacement – at the organic-inorganic interface. The developed themes are summarized below.


Photoactive hybrid systems POM/organoammonium (a), POM/sulfonium (b), POM/spiropyran (c), and POM/spirooxazine (d)


 1. POM/Organoammonium hybrid systems

In these materials, POMs are linked to organoammonium cations (OACs) through hydrogen-bonding networks (Figure 1a). The photochromism originates from a synergetic mechanism which involves the H-bonding sub-network at the organic-inorganic interface. The color change is due to the UV-induced photoreduction of the POM concomitant with an electron transfer assisted by H atom displacement from the OAC towards the POM. The photogenerated coloration is highly tunable by varying the composition and the topology of the POM units (Figure 1b). The coloration rate depends on the nature of the OAC, and it is strongly correlated to the homolytic dissociation energy of the N-H bond (Figure 1c).

Figure 1a. POM/OAC hybrid systems
Figure 1b. tunable colors with the POM’s topology
Figure 1c. Adjustable coloration rates with OACs


Polyoxomolybdate Bisphosphonate Heterometallic Complexes: Synthesis, Structure, and Activity on a Breast Cancer Cell Line
A. Saad, W. Zhu, G. Rousseau, P. Mialane, J. Marrot, M. Haouas, F. Taulelle, R. Dessapt, H. Serier-Brault, E. Rivière, T. Kubo, E. Oldfield, A. Dolbecq, Chem. Eur. J. 21, 10537 (2015)

Fully Oxidized and Mixed-Valent Polyoxomolybdates Structured by Bisphosphonates with Pendant Pyridine Groups: Synthesis, Structure and Photochromic Properties
O. Oms, T. Benali, J. Marrot, P. Mialane, M. Puget, H. Serier-Brault, P. Deniard, R. Dessapt, A. Dolbecq, Inorganics 3, 279 (2015)

Tuning the Photochromic Properties of Molybdenum Bisphosphonate Polyoxometalates
H. El Moll, A. Dolbecq, I. Mbomekalle, J. Marrot, P. Deniard, R. Dessapt, P. Mialane, Inorg. Chem. 51, 2291 (2012)

Smart Heterostructures for Tailoring the Optical Properties of Photochromic Hybrid Organic-Inorganic Polyoxometalates
R. Dessapt, M. Gabard, M. Bujoli-Doeuff, P. Deniard, S. Jobic, Inorg. Chem. 50, 5671 (2011)

Kinetics of Coloration in Photochromic Organoammonium Polyoxomolybdates
R. Dessapt, M. Collet, V. Coué, M. Bujoli-Doeuff, S. Jobic, C. Lee, M.-H. Whangbo, Inorg. Chem. 48, 574 (2009)

Synthesis, Characterizations and Photochromic Properties of Hybrid Organic-Inorganic Materials Based on Molybdate, DABCO and Piperazine
V. Coué, R. Dessapt, M. Bujoli-Doeuff, M. Evain, S. Jobic, Inorg. Chem. 46, 2824 (2007)

2. POM/Sulfonium hybrid systems

We have highlighted that sulfonium polyoxometalates develop efficient solid-state photochromism under a low power UV irradiation in ambient conditions. Such hybrid systems are obtained by self assembling or by covalent grafting of the sulfonium cation onto the POM units and their photoinduced coloration can be modulated by playing with the nature of the POM unit. (see for examples Rb0.75(NH4)5.25[(Mo3O8)2O(O3PC(CH2S(CH3)2)OPO3)2]·8H2O (Mo6(Sulf)2) et (Me3S)4[Mo8O26] (Mo8(Sulf)4) (Figure 2),The photochromism is due to the photoreduction of the POM assisted with the strong polarization of the S atom lone electron pair of the sulfonium towards the POM which stabilizes the reduced Mo5+ centers. Importantly, compared to their OAC counterparts, the sulfonium/POM systems are more promising photoactive materials, because the electron transfers at the organic-inorganic interface do not require direct H-bonding interactions between the POM and the organic moiety.


Figure 2. New solid-state photochromic POM/sulfonium materials


Sulfonium Polyoxometalates: A New Class of Solid State Photochromic Hybrid Organic-Inorganic Materials
K. Hakouk, O. Oms, A. Dolbecq, H. El Moll, J. Marrot, M. Evain, F. Molton, C. Duboc, P. Deniard, S. Jobic, P. Mialane, R. Dessapt, Inorg. Chem. 52, 555 (2013)

3. Bistable POM/Spiropyran materials

The association of POMs with photoactive organic molecules such as spiropyrans (SP) has recently opened up the way to new crystallized hybrid materials with exalted solid-state photochromic, multi-photochromic, and electrochromic properties. This work is done in collaboration with a research group of the university of Versailles, France (Institut Lavoisier) in a program aiming at the elaboration of new effective photoresponsive devices for high density 3D optical data storage. In a first approach, we develop new supramolecular assemblies which associate POMs with cationic spiropyrans (Figure 3). These bistable systems show remarkable photocoloration contrasts in the solid state, and the photoisomerization of the spiropyran is highly tunable playing with the nature of the POMs and the design of the hybrid frameworks.


 Figure 3. Solid-state photochromic properties of the bistable material (SP)4[Mo8O26]-2CH3N

In addition, we study the solid-state photo-activity of novel bistable hybrid POMs covalently functionalized by neutral spiropyrans and other spiro-derivatives (Figure 4). The covalent grafting approach allows improving the spiropyran photoisomerization, and solid materials with strong photoresponses can be successfully reached from organic molecules initially nonphotochromic in the crystalline state.


Figure 4. Effective photoresponsive hybrid systems obtained by covalent grafting of neutral spiro-derivatives onto POMs.


Influence of Electronic vs. Steric Factors on the Solid-State Photochromic Performances of New Polyoxometalate/Spirooxazine and Spiropyran Hybrid Materials
C. Menet, H. Serier-Brault, O. Oms, A. Dolbecq, J. Marrot, A. Saad, P. Mialane, S. Jobic, P. Deniard, R. Dessapt, RSC Adv. 5, 79635 (2015)

A High Fatigue Resistant Photoswitchable Fluorescent Spiropyran -Polyoxometalate-BODIPY Single-Molecule
A. Saad, O. Oms, A. Dolbecq, C. Menet, R. Dessapt, H. Serier-Brault, E. Allard, K. Baczko, P. Mialane, Chem. Commun., 51, 16088 (2015)

Design and Optical Investigations of a Spironaphthoxazine/Polyoxometalate/Spiropyran Triad
A. Saad, O. Oms, J. Marrot, A. Dolbecq, K. Hakouk, H. El Bekkachi, S. Jobic, P. Deniard, R. Dessapt, D. Garrot, K. Boukheddaden, R. Liu, G. Zhang, B. Keita, P. Mialane J. Mater. Chem. C 2, 4748 (2014)

New Photoresponsive Charge-Transfer Spiropyran/Polyoxometalate Assemblies with Highly Tunable Optical Properties
K. Hakouk, O. Oms, A. Dolbecq, J. Marrot, A. Saad, P. Mialane, H. El Bekkachi, S. Jobic, P. Deniard, R. Dessapt, J. Mater. Chem. C 2, 1628 (2014)

Photochromic properties of polyoxotungstates with grafted spiropyran molecules
A. Parrot, G. Izzet, L.-M. Chamoreau,; A. Proust, O. Oms, A. Dolbecq, K. Hakouk, H. El Bekkachi, P. Deniard, R. Dessapt, P. Mialane, Inorg. Chem. 52, 11156 (2013)

Photo- and Electrochromic Properties of Covalently Connected Symmetrical and Unsymmetrical Spiropyran/Polyoxometalate Dyads
O. Oms, K. Hakouk, R. Dessapt, P. Deniard, S. Jobic, A. Dolbecq, L. Nadjo, B. Keita, J. Marrot, P. Mialane, Chem. Comm. 48, 12103 (2012)

Functionalized polyoxometalates with intrinsic photochromic properties and their association with spiropyran cations.
J.-D. Compain, P. Deniard, R. Dessapt, A. Dolbecq, O. Oms, F. Sécheresse, J. Marrot, P. Mialane, Chem. Commun. 46, 7733 (2010)

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