Matthieu Maxence Mention

Chalcones present a potentially promising form of natural photoprotection for inclusion in sunscreen formulations. Here, using femtosecond transient electronic absorption spectroscopy and high-level quantum computations, we explore the differing photophysics of two members of the chalcone family: 4,4’-dihydroxychalcone and 4,4’-dihydroxychalcone-α-methoxylate. From experiment, trapped excited-state population in 4,4’-dihydroxychalcone is alleviated by functionalization at the α carbon, affording vast acceleration in nonradiative deactivation. From theory, the ultrashort excited-state lifetime of the α-substituted analog is explained by a barrierless S₁/S₀ conical intersection, providing a route for ultrafast internal conversion, whereas a significant potential energy barrier prohibits the excited system from approaching this conical intersection in the nonsubstituted chalcone. These observations are supported by results from nonadiabatic dynamics simulations. Our investigations elucidate how targeted chemical modifications can perturb potential energy surfaces, resulting in distinct photophysical behaviors. We demonstrate that chalcones’ deactivation mechanisms are sensitive to substitution at the aliphatic bridge connecting the two aromatic rings.

Sinapoyl malate, naturally present in plants, has proved to be an exceptional UV filter and molecular heater for plants. Although there are nowadays industrially relevant sustainable synthetic routes to sinapoyl malate, its incorporation into certain cosmetic formulations, as well as its adsorption on plant leaves, is limited by its hydrophilicity. To overcome these obstacles, it is important to find a way to effectively control the hydrophilic–lipophilic balance of sinapoyl malate to make it readily compatible with the cosmetic formulations and stick on the waxy cuticle of leaves. To this end, herein, we describe a highly regioselective chemo-enzymatic synthesis of sinapoyl malate analogues possessing fatty aliphatic chains of variable length, enabling the lipophilicity of the compounds to be modulated. The potential toxicity (i.e., mutagenicity, carcinogenicity, endocrine disruption, acute and repeated-dose toxicity), bioaccumulation, persistence and biodegradability potential of these new analogues were evaluated in silico, along with the study of their transient absorption spectroscopy, their photostability as well as their photodegradation products.

Food security is fast becoming one of the most pressing issues of the 21^st century. With increasing climate instability, crop growth is now routinely affected by adverse weather patterns, which can result in reduced crop yields and even crop death. We are developing an environmentally responsible molecular heater to help boost plant growth, to expand the geographic regions suitable for such growth and to protect plants against cold weather. Our molecular heater, sinapic diacid (SDA, 2-(4-hydroxy-3,5-dimethoxybenzylidene)malonic acid), acts as a light-to-heat agent, converting solar energy into heat energy delivered to the plant. We have designed and optimised a sustainable chemical synthesis of SDA, characterised its photophysical properties using a combination of steady-state and ultrafast laser spectroscopy techniques and complementary computational studies, assessed its light-to-heat energy transfer performance to plant leaves in vivo, and explored key environmental and toxicological endpoints through in silico studies. Our spot-test results demonstrate that adsorbed SDA efficiently converts solar energy to heat energy, increasing the local plant leaf temperature by ~ 0.2 °C after sustained irradiation, with no alerts to environmental fate and human toxicity, and with impressive resilience to prolonged solar irradiation. Our studies reveal the hitherto untapped potential of molecular heaters such as SDA for helping to boost plant growth and protect plants against climate instability, with transformative potential towards food security.

A photo-reversible and reusable polymer adhesive was designed and synthesized from bio-resources. Six unique monomers were evaluated via structure–property analysis, and the best polymer adhesive performance was optimized using statistical methods.

With an increasing demand for safe and natural products from both industries and consumers, paired with the recent ban of decried molecules (i.e. octinoxate, avobenzone or octocrylene) due to their high negative impact on humans and the environment (i.e. endocrine disruption, coral bleaching), safe bio-based alternatives are a necessary and promising surrogate to substitute current commercialized petroleum-based UV filters. In this context, a class of bio-based molecules, displaying interesting UV-B filtering properties and great photostability were developed from furfural and 5-hydroxymethylfurfural (HMF), using the Knoevenagel condensation with a set of green conditions to minimize the impact on environment. Furthermore, those furfural- and HMF-based molecules demonstrated antimicrobial properties as secondary activity, highly sought by industries. Some furan derivatives being recognized to exhibit toxicological risks, in silico and in vitro assays were conducted and demonstrated the absence of endocrine disruption activity for these new molecules. GRAPHICAL ABSTRACT

Solar exposure of avobenzone, one of the most widely used commercial UVA filters on the market, is known to cause significant degradation. This finding has fueled research into developing photostabilizer molecules. In an effort to provide insight into their stand-alone photoprotection properties, the excited state dynamics of the photostabilizer, 3-(3,4,5-trimethoxybenzylidene) pentane-2,4-dione (TMBP), and its phenolic derivative, 3-(4-hydroxy-3,5-dimethoxybenzylidene) pentane-2,4-dione (DMBP), were studied with ultrafast transient absorption spectroscopy. Solutions of TMPB and DMBP in ethanol and in an industry-standard emollient, as well as TMBP and DMBP deposited on synthetic skin mimic, were investigated. These experiments were allied with computational methods to aid interpretation of the experimental data. Upon photoexcitation, these photostabilizers repopulate the electronic ground state via nonradiative decay within a few picoseconds involving a twisted intramolecular charge transfer configuration in the excited state, followed by internal conversion and subsequent vibrational cooling in the ground state. This finding implies that, aside from acting as a photostabilizer to certain UV filters, TMBP and DMBP may offer additional photoprotection in a sunscreen formulation as a stand-alone UV filter. Finally, TMBP and DMBP could also find applications as molecular photon-to-heat converters.

The recent ban of some organic UV-filters – such as oxybenzone or octinoxate – considered toxic for coral reef, has heightened the need for eco-friendly alternatives, especially those synthesized using green approaches that reduce the carbon footprint. In this context, several thiobarbituric acid derivatives were synthetized from bio-based p-hydroxybenzaldehydes (e.g. vanillin, syringaldehyde) through a high-yielding sustainable Knoevenagel condensation, and their UV-filtering activity, stability and antiradical properties were investigated. The results showed promising UVA and blue light coverage over time, as well as competitive EC₅₀ values in comparison to commercial antioxidants (i.e. BHA and BHT). In order to evaluate the potential of these molecules as substitutes to current petroleum-based UV-filters, the potential toxicity and fate in environment of these new compounds were evaluated in silico. This screening did not show a critical potential for toxicity, making them promising candidates for further in vitro and in vivo assessment. GRAPHICAL ABSTRACT

Lignocellulose-derived p-hydroxycinnamic acids possess the photo-responsive reversible α,β-unsaturated ester moiety, a reactive structural feature that functions as the basis of the photo-reversible [2 + 2] cycloaddition reaction. To explore the potential of these naturally occurring compounds in the field of self-healing materials, novel bio-based photo-crosslinkable lignin- and glycerol-derived polyfunctional monomers having cinnamate groups were produced using a sustainable process from vanillin and syringaldehyde, two compounds readily obtained from the oxidation of lignin. Through a Structure–Activity Relationship (SAR) study, the structural design of these bio-based monomers was optimized with regards to the crosslinking/decrosslinking extent and the self-healing capacity of the corresponding polymer material. The lignin- and glycerol-derived tri-functional monomer with 4-O-propyl-ferulate moieties has facilitated the design of a new family of bio-based, environment-friendly and reversible self-healing materials for widespread applications. Computational density-functional theory (DFT) and time-dependent DFT calculations were further used for the verification of the SAR study in terms of dimerization energy of the synthesized monomers.

Light-to-heat conversion materials generate great interest due to their widespread applications, notable exemplars being solar energy harvesting and photoprotection. Another more recently identified potential application for such materials is in molecular heaters for agriculture, whose function is to protect crops from extreme cold weather and extend both the growing season and the geographic areas capable of supporting growth, all of which could help reduce food security challenges. To address this demand, a new series of phenolic-based barbituric absorbers of ultraviolet (UV) radiation has been designed and synthesised in a sustainable manner. The photophysics of these molecules has been studied in solution using femtosecond transient electronic and vibrational absorption spectroscopies, allied with computational simulations and their potential toxicity assessed by in silico studies. Following photoexcitation to the lowest singlet excited state, these barbituric absorbers repopulate the electronic ground state with high fidelity on an ultrafast time scale (within a few picoseconds). The energy relaxation pathway includes a twisted intramolecular charge-transfer state as the system evolves out of the Franck–Condon region, internal conversion to the ground electronic state, and subsequent vibrational cooling. These barbituric absorbers display promising light-to-heat conversion capabilities, are predicted to be non-toxic, and demand further study within neighbouring application-based fields.

Thanks to its remarkable properties such as sustainability, compostability, biocompatibility, and transparency, poly-l-lactic acid (PLA) would be a suitable replacement for oil-based polymers should it not suffer from low flexibility and poor toughness, restricting its use to rigid plastic by excluding elastomeric applications. Indeed, there are few fully biobased and biodegradable transparent elastomers–PLA-based or not–currently available. In the last decades, many strategies have been investigated to soften PLA and enhance its toughness and elongation at break by using plasticizers, oligomers, or polymers. This work shows how a ferulic acid-derived biobased additive (BDF) blends with a common rigid and brittle commercial grade of polylactic acid to provide a transparent non-covalently cross-linked elastomeric material with shape memory behavior exhibiting an elongation at break of 434% (vs 6% for pristine PLA). Through a structure–activity relationship analysis conducted with BDF analogues and a modeling study, we propose a mechanism based on π–π stacking to account for the elastomeric properties. Blending ferulic acid derivatives with polylactic acid generates a new family of fully sustainable transparent elastomeric materials with functional properties such as shape memory.