Julien Boixel

CNRS Researcher Fellow

Email : julien [dot] boixel [at] univ-rennes1 [dot] fr

Phone : +33 (0) 2 23 23 31 67

Office number : 927 - Build. 10C

CNRS Researcher Fellow

Researcher unique identifier (ORCID) : 0000-0001-8704-8776

UMR 6226 CNRS-Université de Rennes 1, Institut des Sciences Chimiques de Rennes, Campus de Beaulieu, 35042 Rennes, France

Curriculum Vitae

Education

2019. Accreditation to supervise research (HDR). Université de Rennes / Institute of Chemical Sciences of Rennes – UMR-CNRS 6226 / France

2009. PhD in organic chemistry. Université de Nantes – laboratoire CEISAM. Under supervision of Dr. Fabrice ODOBEL. "Synthèse et caractérisation d’édifices moléculaires pour la séparation et l’accumulation de charges photo-induites".

2006. Master degree in chemistry. Université de Nantes

Professional experience

2011 – 2012. Postdoctoral research associate. ENS Cachan / Institut des Sciences Chimiques de Rennes with Dr. Keitaro NAKATANI / Dr. Véronique Guerchais. Organometallic chemistry.

2010 – 2011. Postdoctoral research associate. University of Geneva (UNIGE) with Prof. Stefan MATILE. Supramolecular organic chemistry.

Fundings

2019-2023. ANR JCJC PhotoControl, 183 k€, coordinator.

2019-2021. Programme de Recherche Conjoint PRC, 21 k€ granted by the CNRS, coordinator in collaboration with Dr. Keith Man-Chung Wong, SUSTC, China.

2018-2019. Programme d’attractivité doctorale, 21 k€ granted by the Université Bretagne Loire, coordinator in collaboration with Dr. Rémi Dessapt, Institut des Matériaux Jean Rouxe.

2018. Programme Boost’ERC, 16.5 k€ granted by La Région Bretagne, coordinator.

2018. Défis Scientifiques, 10 k€ granted by the Université de Rennes 1, coordinator

2016. PHC Galilée with the University of Milano (Italy), scientific partner.

2016. PICS with the University of Milano (Italy), scientific partner.

2015. Allocation d’Installation Scientifique (AIS), 20 k€ granted by Rennes Metropole.

Responsibilities

Treasurer of the Société Chimique de France – Bretagne Pays de Loire.

Prevention officer at the Institut des Sciences Chimiques de Rennes.

Research interests

The common thread running through my research interests is the development of molecules for molecular photonics. It is mainly based on a molecular engineering approach including chromophores design and organometallic complexes chemistry for the synthesis of new molecular materials precursors for luminescence and nonlinear optics (NLO). An important aspect of these investigations deals with the control of the optical properties via the photo-isomerization a dithienylethene (DTE) photochromic unit. By combining photochromism with a second optical property such as luminescence or NLO, new multi-functional molecular systems can be achieved.

DTE as electronic modulator

Photochromic Cyclometalated Platinum Complexes: Second-Order NLO Switches from Molecules to Polymer Films

Novel photochromic dithienylethene-based platinum(II) complexes (C^N^N)Pt(C≡C-DTE-C6H4-D) were prepared and characterized. Their excellent photochromic properties allow the photoinduced switching of their second-order nonlinear optical properties in solution, as measured by the EFISH technique, due to formation of an extended π-conjugated ligand upon suitable electromagnetic radiation. Insights into the electronic structures of the complexes and the nature of their excited states have been obtained by DFT and TD-DFT calculations. These novel Pt(II) complexes were nanoorganized in polymer films which were polled, affording new materials characterized by a good second-order NLO response that can be easily switched, with an excellent NLO contrast. To the best of our knowledge, our compounds allowed designing the very first examples of switchable NLO polymer films based on metal complexes.

A new type of DTE-based platinum complex have been prepared where the organometallic fragment and the dialkylaminophenyl group are located on the same thiophene ring of the photochromic DTE unit (rather than at both ends of the DTE unit as for the previous system), the cyclometalated Pt(II) acetylide moiety being bounded to one of the reactive carbon atoms. This design gives rise to an extended p-conjugated alkynyl ligand in the open form, accompanied by metal-to-ligand–ligand-to-ligand charge transfer (MLCT/LLCT) transitions. In contrast, the formation of a tetrahedral center at the C2 carbon in the closed form induces a new conjugated pathway centered on DTE. Moreover, the introduction of a strong donating dialkylamino end group allows us to dramatically modify the electronic structure by protonation. This unprecedented DTE-based Pt(II) complex stands as the first example of a sequential double nonlinear optical switch, induced first by protonation and next upon irradiation with UV light.

The DTE as structuring unit

Another challenge is the photo-control of the p-p and metal-metal interactions at the supramolecular level for NIR luminescence. Accordingly, we designed a set of two DTE-based di-nuclear of Pt(II) complexes, Pt-A and Pt-B With the aim of reversibly controlling the supramolecular interactions between two Pt(II) fragments thanks to the introduction of a photoisomerizable central DTE spacer. Pt-A displays a "normal" design whereas the Pt(II) acetylide fragments are linked to the reactive carbon atoms ("reverse" design) in Pt-B.  In addition to the closed form, the possible conformations of the parallel (P) and antiparallel (AP) isomers of the DTE in the open forms offer several possible interaction modes between the two Pt(II) fragments. Remarkably, Pt-A ​​can be efficiently photo-converted into its closed form upon irradiation at 350 or 450 nm (> 90 % of openclosed conversion estimated by proton NMR). Conversely, Pt-B exhibits no photochromism under the same conditions which is surprising given the adequate molecular orbitals topology on the reactive carbons of the AP open form for a ring-closure reaction. In fact, stabilizing interactions (p-stacking interactions between terminal phenyl rings and the N^N^C ligands) are calculated in AP open form of Pt-B but not in its closed form that is much less stable (> 35 kcal mol-1).

The locked structure for Pt-B in its AP conformation forces the terminal phenyl ring and the N^N^C ligand to interact with each other through p-p stacking interaction. The ca. 4 Å distance between the centroids of the terminal phenyl and the centroid of the central pyridine ring hints for weak p-stacking interactions at the ground state that turned to be operative at the triplet state giving rise to excimer luminescence in the near infra-red (760 nm) upon 436 nm excitation.

Publications

Publications referenced in HAL since 2006