Minh-Huong Ha-Thi

Three complex ferrocene‐BODIPY‐fullerene‐peptide conjugates were synthesized by successive CuAAC reactions between firstly ferrocene‐BODIPY azides, then a lipoyl peptide azide, with a dual‐clickable fullerene platform. These conjugates displayed broad absorption in the visible region due to their extended π‐conjugation and the presence of an intramolecular charge transfer band from ferrocene to BODIPY, particularly in the case of BODIPY derivatives functionalized at the beta and alpha positions with ethynylFc and vinylFc groups, respectively. The terminal lipoyl peptide allowed grafting of the conjugates on gold surfaces, to form self‐assembled monolayers that were characterized by PM‐IRRAS and ultrafast electrochemical techniques. Estimation of the heterogeneous electron transfer rate constants for these monolayers revealed higher values for electron transfer from the BDP or C ₆₀ entities to the metal surface compared with conjugates without ferrocene units. This could be attributed to a reduced distance between the (Fc) ₂ ‐BODIPY‐C ₆₀ part and the metal surface, due to folding of the conjugates within the monolayer.

Photoinduced electron transfer in an earth-abundant Cu( i ) photosensitizer generates a reduced species capable of activating a CO ₂ reduction catalyst, as revealed by time-resolved spectroscopy and DFT calculations.

A biobased hydroxyanthraquinone dye derived from alizarin was shown to be an efficient visible-light photosensitizer for iodonium salt, leading high acrylate conversions (around 80%) up to 470 nm through a type II photoinitiation process.

Identifying systems composed of earth-abundant elements capable of photoinduced electron-transfer represents a major breakthrough for the development of sustainable photocatalytic processes. Herein, we demonstrate that octahedral tungsten-halide clusters constitute a promising new class of robust photosensitizers, owing to their exceptional chemical stability, intense luminescence, and long-lived triplet excited states. Upon irradiation in aqueous solution, these species transfer an electron to polyoxometalates (POMs), well-known molecular catalysts capable of multielectron redox chemistry. More specifically, we investigate the photophysical properties of supramolecular systems combining the cluster-based motif [{W₆Iⁱ₈}Cl^a₆]^2– and a series of archetypal POMs ([PW₁₂O₄₀]^3–, [SiW₁₂O₄₀]^4–, [BW₁₂O₄₀]^5–, [P₂W₁₈O₆₂]^6–) as electron-acceptor units, in the presence of γ-cyclodextrin (γ-CD), which acts as both a supramolecular assembly scaffold and a stabilizing agent. The photoinduced electron-transfer process was investigated using steady-state and time-resolved optical spectroscopy, complemented by spectro-electrochemical measurements, which unambiguously confirm electron transfer from the excited cluster to the POMs. Furthermore, we demonstrate that both the ionic charge of the POMs and the presence of γ-CD significantly influence the efficiency of the process. This work highlights the dual role of γ-CD, which facilitates the association of two negatively charged inorganic units and stabilizes the charge-separated state by maintaining an appropriate spatial arrangement within the supramolecular assembly.

CO₂ electroreduction to multicarbon products using Cu-based catalysts is one of the strategies currently developed in order to valorize CO₂ and store electricity. Molecular modification of material surfaces has been recently explored in order to tune the reactivity of Cu catalysts and improve their selectivity toward C₂₊ products, in particular ethylene and ethanol. Here, we compare four classes of precursors of aryl radicals, namely, aryl-iodoniums, -diazoniums, -sulfoniums, and -silicates, which are used for grafting an aromatic layer onto the surface of Cu nanoparticles via electroreduction or electrooxidation. In all cases, the surface modification promotes CO-CO coupling and C₂₊ product formation, leading to a much higher FE_C2+/FE_CO (FE = Faradaic efficiency) ratio. However, we show that the composition of the layer is more complex and diverse than anticipated and likely explains the unexpectedly large variations in selectivity, even though the Cu catalysts were functionalized with presumably the same aromatic layer derived from the same aryl radical generated by the four different precursors. These classes of precursor salts are thus not interchangeable and provide a much larger scope of Cu surface modifications and Cu catalysts than anticipated to be studied independently.

Understanding the mechanism through which a photochemical reaction proceeds grants access to thermodynamic and kinetic parameters that allow its optimization for large‐scale applications. In the last few years, photocatalytic systems have been major players in scientific developments on research fields of primary importance, including solar fuel generation in artificial photosynthesis, and the use of excited organic radical ions as photocatalysts in thermodynamically challenging reactions of utmost synthetic relevance. Generally, time‐resolved spectroscopic approaches are the main experimental tools to investigative the dynamics of photoactive systems, with pump‐probe‐based ones being the golden standard in photophysical and photochemical research. However, for photocatalytic systems in which multiple photons are required, which is generally the case for photosynthetic reactions and those promoted by excited organic radical ions, the pump‐probe approach is no longer sufficient since it is based on a single photon‐to‐electron ratio. This is where a second actinic pump excitation comes into play in what is known as pump‐pump‐probe spectroscopy. In this review, we explore how this approach is used to unravel the mechanism of photocatalytic systems triggered by light using different probes of UV–vis absorption and resonance Raman scattering in varying time scales.

We have prepared lycopene aggregates with low scattering in an acetone-water suspension. The aggregates exhibit highly distorted absorption, extending from the UV up to 568 nm, as a result of strong excitonic interactions. We have investigated the structural organization of these aggregates by resonance Raman and TEM, revealing that the lycopene aggregates are not homogeneous, containing at least five different aggregate species. Transient absorption measurements upon excitation at 355, 515, and 570 nm, to sub-select these different species, reveal significant differences in dynamics between each of the aggregate types. The strong excitonic interactions produce highly distorted transient electronic signatures, which do not allow an unequivocal identification of the excited states at times shorter than 60 ps. However, these experiments demonstrate that all the lycopene aggregated species form long-living triplets via singlet fission.

This study demonstrates that water-soluble perylene-derivative dimers can efficiently induce either singlet fission or charge separation upon photoactivation.

We provide direct evidence of singlet fission occurring with water-soluble compounds. We show that perylene-3,4,9,10-tetracarboxylate forms dynamic dimers in aqueous solution, with lifetimes long enough to allow intermolecular processes such as singlet fission. As these are transient dimers rather than stable aggregates, they retain a significant degree of disorder. We performed a comprehensive analysis of such dynamic assemblies using time-resolved absorption and fluorescence spectroscopy, nuclear magnetic resonance spectroscopy, and theoretical modelling, allowing us to observe the characteristic signatures of singlet fission and develop a model to characterize the different species observed. Our findings reveal that structure fluctuations within perylene-3,4,9,10-tetracarboxylate associations are key in favoring either singlet fission or charge separation. The efficiency of triplet formation is higher than 100%, and the disordered system leads to triplets living in the nanosecond time range.