Denis Frath

Denis Frath obtained his PhD in chemistry from the University of Strasbourg in 2013 (laboratory of Dr. Gilles Ulrich and Raymond Ziessel). His doctoral work, supported by a MENRT scholarship, focused on hydrogen production using light and the synthesis of new fluorescent dyes. He then joined the Matsuda laboratory to work on photoresponsive self-assembled monolayers as a JSPS postdoctoral fellow at Kyoto University (2013-2015). After that, he worked on redox-active molecular layers for electronic devices at Paris Diderot University (2016-2017) and binuclear phthalocyanine metallic complexes for catalytic reactions at CNRS in Lyon (2018).

Since 2018, he is CNRS researcher at the Chemistry Laboratory of ENS Lyon where he is head of the Supramolecular Chemistry and Chemical Biology group. His research interests are directed towards π‐conjugated molecules with optical and electrochemical properties, their supramolecular self-assembly and functional materials with switchable properties (gels, liquid crystals, surfaces…). In 2024, he was awarded the SP2P Young Researcher Prize (French Chemical Society).

Our article is available to read at ACS Omega.We describe a very simple and efficient gram-scale synthetic pathway toward Boranils substituted directly on the boron center by 1,1′-bi-2-naphthol derivatives (BINOL). Properties of the resulting BINOL-Boranils were investigated by nuclear magnetic resonance (NMR), UV–visible, fluorescence, electronic circular dichroism (ECD), and circularly polarized luminescence (CPL) spectroscopies. Insight into the molecular structure is also provided based on single-crystal X-ray diffraction experiments. These chiral dyes typically feature high molar absorption coefficients in the range of 35,000 to 90,000 M^–1·cm^–1, absorption dissymmetry factors (g_abs) in the range of 2.5–5.5 × 10^–4 at the maximum wavelength of absorption of Boranils, and CPL brightness up to B_CPL = 5.4 M^–1·cm^–1.

Our article is available to read at J Mater. Chem. C.

Organo-bridged polysilsesquioxanes (PSQ) incorporating photo- and electroactive motifs are promising candidates for optoelectronic and ion-conductive materials. We report the synthesis of PSQ gels incorporating redox- and photo-sensitive naphthalene diimide (NDI) units capable of self-assembly via π–π interactions. Two distinct synthetic routes were explored: the first offering simplicity and quick access to the targeted materials, the second being longer but bringing better control of their composition. The NDI-PSQ gels obtained by these two different routes were exhaustively characterized using rheology, XRD, fluorescence, spectroelectrochemical, electrochemical, impedance, NMR, and IR spectroscopy measurements. Both routes yield gels with similar morphological characteristics but exhibit notable differences in the aggregation modes of the NDI motifs. The NDI-PSQ gels exhibit dual emission states (λ_em = 450 and 550 nm) attributed to the coexistence of at least two distinct aggregate domains. The remarkable ionic conductivity of NDI-PSQ gels is also particularly interesting for considering applications in optoelectronics. Overall, this study provides new insights into the design and applications of redox/photo-responsive PSQ-based gels.

Our article is available to read at Chem. Eur. J.

Herein we report one of the very first supramolecular gel for which the formation and dissociation of the self-assembled network can be achieved using an electrochemical stimulation. The redox-triggered macroscopic changes under different photochemical or electrochemical stimuli result from the reversible assembly of charge transfer complexes formed between the viologen acceptor and iodide counter-anions.

Our article is available to read at J. Org. Chem.

We describe herein the synthesis along with full photophysical and computational studies of three series of boranil complexes (Series I−III), incorporating extended ethynyl substitution, either on the imino side (Series I), on the phenolic side (Series II), or on both sides (Series III), in order to assess the impact of the insertion of electron donors or acceptors on the fluorescence properties. A full photophysical study in solution (various solvents) demonstrated the presence of a strong intramolecular charge transfer process within these boron complexes, with fluorescence colors spanning the entire visible range. Additionally, these compounds are also emissive in the solid state, on a similar wide fluorescence range, thus providing more examples of dual solution- and solid-emissive fluorophores, based on boron complexes. Theoretical calculations on both anil ligands and boranil complexes rationalize the charge transfer nature of the excited states involved in the emissive transitions.

Our article is available to read at Chem. Sci.

The present article reports on a new and efficient synthetic strategy towards tetracene-bipyridiniums. On the basis of extensive experimental analyses supported by DFT simulations, we report the first observation of a mixed valence complex formed in solution under standard conditions from an unconstrained bis-viologene derivative.

Our article is available to read at Soft Matter.

Supramolecular crystal gels, a subset of molecular gels, are formed through the self-assembly of low molecular weight gelators into interconnecting crystalline fibers, creating a three-dimensional soft solid network. This study focuses on the formation and properties of viologen-based supramolecular crystalline gels. It aims to answer key questions about the tunability of network properties and the origin of these properties through in-depth analyses of the gelation kinetics triggered by thermal quenching. Experimental investigations, including UV-Vis absorption spectroscopy, rheology, microscopy and scattering measurements, contribute to a comprehensive and self-consistent understanding of the system kinetics. We confirm that viologen-based gelators crystallize by forming nanometer radius hollow tubes that assemble into micro to millimetric spherulites. We then show that crystallization follows the Avrami theory and is based on pre-existing nuclei. We also establish that the growth is interface-controlled, leading the hollow tubes to branch into spherulites with fractal structures. Finally, we demonstrate that the gel properties can be tuned depending on the quenching temperature. Lowering the temperature results in the formation of denser and smaller spherulites. In contrast, the gel’s elasticity is not significantly affected by the quench temperature, leading us to hypothesize that the densification of spherulites occurs at the expense of connectivity between spherulites.

Our article is available to read at J. Phys. Chem. C.

In the present work, two viologen derivatives were synthesized and used in molecular junctions (MJs) to investigate the impact of a decoupling unit on the rectification behavior. Both bear an aniline terminal unit but one of the viologen derivative (named VIO-C₁) is terminated by a methyl group whereas the other (named VIO-C₆) bears a six-carbon (C₆H₁₃) terminal chain. Thin layers of each derivative were deposited on gold microelectrodes by the electroreduction of the corresponding diazonium reagents, and solid-state MJs were fabricated to study the electronic transport. JV curves of VIO-C₁ show a symmetric behavior, whereas the VIO-C₆ (with alkyl chain) JV curves show strong asymmetry in the transport. This behavior is attributed to the decrease of the electronic coupling at the top interface due to the alkyl chain and is confirmed by comparison with similar VIO-C₁ MJs in which a thin AlO_x layer is inserted on top of the VIO-C₁ layer. The impact of this decoupling unit on the rectification ratio is discussed.

Our article is available to read at J. Mater. Chem. C.

Naphthalenediimide amphiphiles (NDI-as) with quaternary ammonium groups (DC4, DaP, and DaO) display unprecedented UV light-induced aggregation in solutions of water, acetonitrile and THF. Light-induced aggregation brings significant spectral modification by which unusual absorption band distribution is assigned to H-type aggregates. Such aggregation can be reversibly broken by heating and reassembled by photoirradiation. The irradiation/heating cycles that provoke assembly/disassembly process can be confirmed by ¹H-NMR spectroscopy. The possibility of a chemically promoted aggregation by or radical anion either anion–π interaction may be ruled out by UV-Vis, EPR and electrochemistry measurements. These photoinduced aggregates can sensitize dissolved O₂ to produce singlet oxygen, a surprising observation when it comes to sensitization efficiency for dyes as aggregation usually decreases sensitization yield. Laser-induced luminescence measurements corroborate the existence of monomeric and aggregate forms, as well as confirm triplet states as phosphorescence was detected, being particularly intense in concentrated THF solutions.

Ambition Internationale (2024-2026)

“On-surface chiroptical properties in self-assembled monolayers for photonics and optoelectronics”

Partners involved :
P1 : UMR 5182 – Laboratoire de Chimie, ENS Lyon (Coord. D. Frath)
P2 : UMR 5306 – ILM, Université Claude Bernard Lyon 1 (S. Guy)
P3 : Nara Institute of Science and Technology (T. Kawai)
P4 : Graduate School of Engineering, Kyoto University (K. Matsuda)

Our article is available to read at J. Mater. Chem. C.

Redox-active conductive supramolecular gels involving highly ordered chiral assemblies of small organic molecules are very promising soft materials for many applications ranging from catalysis to electronics. However, combining all these properties in the same material has so far remained a difficult task. We now report the synthesis and detailed structural, rheological, and electrical characterizations of supramolecular gels obtained by self-assembly of a dicationic low molecular weight gelator incorporating a redox-active 4,4′-bipyridinium unit. These molecules have been shown to self-assemble in pentanol to form chiral hollow core–shell cylinders, eventually yielding dendritic clusters inducing gelation. We also showed that the optical, rheological, and electrical properties of the gels can be tuned by adding ionic additives. Careful control of the formation of charge-transfer complexes between viologens and iodides has led to the formation of robust, transparent, conductive, and chiral gel. The gelation process, the properties of the gel, and the structure of the assemblies have been thoroughly investigated by UV-Vis and ECD spectroscopy, rheometry, bright-field microscopy, SAXS, AFM, electrochemical and impedance measurements.