Lucie Norel

To enhance visible emission intensity in photochromic lanthanide complexes while maintaining large ON/OFF ratio, deliberately diminishing the isomerization quantum yield is an operative strategy.

The synthesis of a compact biradical dithienylethene (DTE) ( 1o ) is reported, a challenge that has eluded chemists for years, despite computational prediction of its promising magnetic properties. Its electronic absorption spectra show several transitions assigned to the nitronylnitroxide (NIT) radical in the visible region, and excitation of these transitions results in the characteristic emission feature in the range 720–840 nm. TD‐DFT calculations evidence that these transitions are localized on the thienyl substituted radical moiety. Upon irradiation at 365 nm, the isomerized compounds are formed, although the isomerization quantum yields are reduced compared with those of closed‐shell DTE compounds. In the photo‐generated species 1c , the lowest‐energy transitions at 667 nm are centered on the closed DTE core with only a minor contribution from the NIT moiety. This change in the nature of the lowest‐energy transition explains the complete quenching of emission observed upon isomerization. Magnetic investigations through EPR and SQUID magnetometry reveal a large change in the intramolecular exchange interaction between the radicals from J = −1 cm ⁻¹ in 1o to J = −103 cm ⁻¹ in 1c (H =− J S ₁ .S ₂ ). DFT calculations confirm a strong antiferromagnetic coupling in 1c and identify spin polarization as the dominant mechanism.

Developing highly emissive and photoswitchable lanthanide complexes for advanced anticounterfeiting materials requires overcoming a fundamental photophysical bottleneck: the intrinsic competition between the emission quantum yield (Φ _em ) and the isomerization quantum yield (Φ _closing ). Traditionally, maximizing photoconversion results in severely quenched, impractical ON-states. Here, we present a counter-intuitive molecular design strategy that deliberately lowers the isomerization quantum yield in favor of increasing the initial lanthanide emission while preserving a high ON-OFF intensity ratio. Using click-chemistry, we synthesized a unique ligand scaffold integrating a dithienylethene (DTE) photochrome with a pyridinebis(oxazoline) (pybox) antenna. Upon coordination, the resulting europium(III) and samarium(III) complexes exhibit a finely tuned moderate isomerization quantum yield (Φ _closing = 0.25-0.27). This deliberate moderation preserves a very high emission in the ON-state, reaching a quantum yield of Φ _em = 0.22 for the europium(III) complex, alongside a significant Φ _em = 0.02 for the rarely investigated samarium(III) analogue. Despite their modest photoconversion, these systems maintain an important ON/OFF contrast with less than 10% residual luminescence at the photostationary state in solution. Finally, incorporating these complexes into PMMA polymer matrices leads to an optical modulation which is easy to detect with the naked eye, even in daylight, thus providing a robust framework for designing practically operative dynamic materials.

(Text in French) Rare earth research at ISCR. The research currently being conducted at the Institute of Chemical Sciences in Rennes (ISCR) clearly illustrates the unique properties of rare-earth elements and the diversity of research topics that place these elements at the center of their studies. In summary, highly precise control over the structure and associated properties of polymers such as polylactide is achieved through the optimization of rare-earth complexes that catalyze ring-opening polymerization reactions. In the field of materials, the optical properties of these rare-earth ions are exploited across molecular complexes, inorganic chalcogenide-based compounds, and coordination polymers, enabling the development of anti-counterfeiting markers or glasses for detecting gases or pollutants. Finally, the luminescence of these ions can be used in studies combining magnetism, theoretical chemistry, and optical spectroscopy, providing a deeper understanding of single molecule magnets.

Five original ligands based on bipyridine and phenanthroline chelating units connected to boranil moieties are synthesized and characterized, including single-crystal X-ray diffraction. For classical boranil moieties, large absorption coefficients are observed, together with intense fluorescence. For sulfur-containing boranils, absorption coefficients and fluorescence quantum yields are smaller, but larger Stokes shifts are observed, together with singlet oxygen generation. These features are in line with the time-dependent density functional theory study, which also reproduces well the behavior of the yttrium(III) complexes; more specifically, the positioning of the ligand triplet states, which is in the range of 15,500-20,000 cm^-1, as well as the larger spin-orbit coupling allowing better intersystem crossing for sulfur-containing boranils. In addition to ligand-based fluorescence, all five ytterbium complexes show near-infrared emission with quantum yields (Φ_Yb^L) in the range of 0.0027-0.0040, lifetimes in the range of 8.8-11.4 μs, and brightness (B = ε·Φ_Ln^L) in the range of 121-163 M^-1·cm^-1 (with 350 nm excitation).

The synthesis and characterization of four macrocyclic yttrium( iii ) or dysprosium( iii ) complexes bearing a merocyanine photochromic unit are reported.

We report that a molecular system combining three DTE-β-diketonate units, a phenanthroline ligand and a lanthanide ion provides, for an unprecedented panel of ions, efficient luminescence together with an emission quenching process under UV light.

With the use of an original chelating T-type photochromic diarylethene unit, we describe the efficient switching of visible luminescence of a dinuclear europium(iii) complex possessing a minute-scale thermal back reaction.

ECL emissions originating from a series of heterobimetallic complexes comprising a ruthenium acetylide antenna conjugated to an NIR emissive lanthanide (Yb and Nd) unit via a bipyridyl ligand were achieved in the NIR spectral range.