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Topic 2: Photochromic metal complexes for the modulation of luminescence and nonlinear optical properties

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Dr Hubert Le Bozec / Dr Véronique Guerchais / Muriel Escadeillas / Dr Julien Boixel

Photochromic metal complexes for the modulation of luminescence and nonlinear optical properties

We are currently developping the chemistry of photochromic DithienylEthene (DTE) containing bipyridine ligands and their metal complexes (ZnII, IrIII, FeII, RuII, ReI…) for the modulation of their optical, linear and nonlinear, properties.

Multifunctional molecules

Designs of the photochromic DTE units

1-Efficient photoswitching of the nonlinear optical properties of dipolar photochromic zinc(II) complexes

V. Guerchais & H. Le Bozec

PhD : V. Aubert

Collaborations : I. Ledoux, E. Ishow, K. Nakatani (ENS Cachan)

A new type of 2,2’-bipyridine ligands featuring photochromic dithienylethene (DTE) groups, and the corresponding dipolar zinc(II) have been designed. The NLO properties of these metallo-chromophores have been studied by EFISH. This study describes for the first time an efficient ON/OFF photoswitching of the NLO response of metal-containing chromophores.

Angew. Chem. Int. Ed. (2008) 47, 577-580 (VIP)

2-Tunable Double Photochromism of a Family of Bis-DTE Bipyridine Ligands and their Dipolar Zn Complexes

J. Boixel, V. Guerchais & H. Le Bozec

PhD : L. Ordronneau & V. Aubert

Collaborations : R. Métivier, E. Ishow, K. Nakatani (ENS Cachan), A. Boucekkine (Rennes)

The bis-DTE containing bipyridine ligands, display a double photochromism behavior, the two DTE units undergo the photocyclization processes to afford the closed,closed (c,c) form. Moreover, we have demonstrated that the photochromic ring-closure/opening reactions occur in a stepwise fashion with an excellent photo-conversion (> 95 %), for both the free bipyridine ligands and their corresponding Zn complexes.

Photokinetic studies shows very different consecutive quantum yields, which are correlated to the electronic effects of the D end groups and of the bipy-metallic fragment acting as the acceptor group.

3-Linear and Nonlinear Optical Properties of Cationic Bipyridyl Iridium(III) Complexes: Tunable and Photoswitchable ?

V. Guerchais & H. Le Bozec

PhD : L. Ordronneau & V. Aubert

Collaborations J. A. G. Williams (Durham); D. Roberto (Milano); A. Boucekkine (Rennes)

A full investigation on the synthesis, characterization, linear and nonlinear optical properties of a new series of iridium(III) complexes which incorporate extended Ar-vinyl π systems on the bipyridine ligand, is reported. These cationic complexes display large second order NLO responses which can be modulated by the nature of the substituents, as well as by the concentration and nature of the counter-anion. The incorporation of a photochromic DTE unit into the bipyridine ligand allows to switch ON and OFF the luminescence but not the NLO activity.

Inorg. Chem. (2011) 50, 5027-5038

4-Photochromic Metal Complexes : Photoregulation of Both the Nonlinear Optical and Luminescent Properties

H. Le Bozec & V. Guerchais

PhD : L. Ordronneau & H. Nitadori (Tokyo)

Collaborations I. Ledoux (ENS Cachan), J. A. G. Williams (Durham), M. Akita (Tokyo)

A series of dithienylethene (DTE)-containing 2,2’-bipyridine ligands and their zinc(II), rhenium(I) and ruthenium(II) complexes have been designed and synthesized, and their photochromic, photophysical, and quadratic nonlinear optical properties have been studied. The NLO study describes an efficient ON/OFF photoswitching of the NLO response of these metal-containing chromophores. Moreover, the combination of the photochromic DTE-based bipyridine ligand with luminescent Re(I) and Ru(II) fragments allows the photoregulation of the emission, leading to an efficient quenching of the luminescence

Inorg. Chem. (2012) 51, 5627-5636

5-Photoswitching of the second-order nonlinearity of a tetrahedral octupolar multi DTE-based copper(I) complex

J. Boixel, V. Guerchais & H. Le Bozec

PhD : L. Ordronneau & H. Nitadori (Tokyo)

Collaborations : D. Jacquemin (Nantes) ; I. Ledoux (ENS Cachan)

The modulation of the quadratic NLO response of an octupolar copper complex containing four photochromic units is reported for the first time. As evidenced by absorption spectroscopy and supported by DFT calculations, the NLO response is controlled by the full photohromism of the four DTE units. The molecular first hyperpolarizability is increased more than six fold with DTE ring-closure, to reach the impressive Betaxyz value of 2212 × 10-30 esu.

Chem. Commun. (2012) 48, 10395-10397

6-The first hexa–dithienylethene tris(bipyridine)metal complexes as quadratic NLO photoswitches: Combined experimental and DFT studies

H. Le Bozec & V. Guerchais

PhD : L. Ordronneau & V. Aubert

Collaborations : D. Jacquemin (Nantes) ; I. Ledoux (ENS Cachan)

Flip the NLO switch ! A straightforward access to hexa-DTE based photochromes by using a coordination chemistry approach through the combination of bis-DTE bipyridyl ligands and metal ions (M = Zn, Fe) is reported. The photostability of the isomeric forms of the iron(II) complexes allows the photoswitching of second-order NLO responses, and the results are rationalized with the help of TD-DFT.

Chem. Eur.J. (2013) DOI: 10.1002/chem.201300517

7-A “reverse interruptor”: novel molecular design of a fluorescent photochromic DTE-based bipyridine

J. Boixel, H. Le Bozec & V. Guerchais

PhD : L. Ordronneau & V. Aubert

Collaborations E. Ishow, K. Nakatani (ENS Cachan); J. A. G. Williams (Durham); A. Boucekkine (Rennes)

An original design of a fluorescent dithienylethene-based bipyridine, where the donor (D) and acceptor (A) groups are located on the same thiophene ring of the DTE unit is reported; in non-polar solvents, excitation in the UV or visible triggers the photochromic reaction, disrupting the conjugation and quenching the fluorescence.

New J. Chem. (2009) 33, 1320-1323

Palladium-catalysed C-H bond activation

Collaboration Henri Doucet (Rennes)

1-Palladium-catalysed direct arylation of a tris-cyclometallated Ir(III) complex

H. Doucet, V. Guerchais

PhD : M. Zaarour, K. Beydoum

Collaboration J. A. G. Williams (Durham)

The palladium-catalysed direct 5-arylation of metallated thiophenes of fac-Ir(N^C3’-thpy)3 with aryl bromides via C–H bond functionalisation allows the synthesis of a variety of new Ir(III) complexes in only one step (thpyH = 2,2’-thienylpyridine). This method offers an easy modification of the nature of the ligand and hence of the photophysical properties of the luminescent complexes.

Chem. Commun. (2012) 48, 1260-1262

2-Direct arylation of dithienylperfluorocyclopentenes via palladium-catalysed C-H bond activation

J. Boixel, V. Guerchais, H. Doucet

PhD : K. Beydoum

We found that Pd-catalysed direct arylation of 1,2-dithienylethene derivatives (DTE) proceeds regioselectively on the C5 position of the thiophene moieties. Mono- and diarylated products were obtained with moderate to good yields. The functional group tolerance of this catalytic method allows a fine-tuning of the photochromic properties.

Catal. Sci. Technol. (2012) 2, 1242-1248

3-A straightforward access to photochromic diarylethene derivatives via palladium-catalysed direct heteroarylation

J. Boixel, H. Doucet, H. Le Bozec, V. Guerchais

PhD : K. Beydoum

Pd-catalysed C-H bond activation is a powerful tool to prepare “reverse” diarylethenes (DAE) such as bis(2-thienyl)ethene and bis(5-thiazolyl)ethene derivatives.

Moreover, this method involves the use of 1,2-dichlorohexafluorocyclopentene as starting material, a more convenient precursor than the toxic and volatile octafluorocyclopentene.

Pd-catalysed alkenylation of heteoarenes by 2-dichlorohexafluorocyclopentene offers a fast and direct access to symmetrical and unsymmetrical 1,2-di(heteroaryl)hexafluorocyclopentenes. A wide range of heterocycles (thiophenes, thiazoles or furans) can be employed and various functions are tolerated. The photochromic properties of these new DAE have been studied by UV-vis. and NMR spectroscopy.

Chem. Commun. (2012) 48, 11951-11953

Organometallic Luminophores

M. Escadeillas, H. Le Bozec, V. Guerchais,

PhD : J. Araya, J. Gayardo

Collaborations S. A. Moya, P. Aguirre (Santiago de Chile), J. A. G. Williams (Durham)

A novel iridium complex incorporating a di(2-picolyl)anilinoappended bipyridine ligand was synthesized and its optical properties studied. The presence of Zn2+ ions specifically perturbs the excited state, giving rise to a blue-shifted absorption and emission, and a shorter luminescence lifetime.

New J. Chem. (2010) 34, 21-24