Intitulé du sujet: Mechanical efficiency of polymeric photoactuators: insights from quantum chemistry
Sujet
Codirection:
Nombre de mois: 48 mois
Ecole Doctorale: ED 388 - Chimie physique et Chimie analytique de Paris centre
Unité de recherche et équipe:
The LIED (“Interdisciplinary Energy Research Institute”, CNRS, Univ. Paris Cité) aims at developing fundamental and applied science in response to the challenges of the “energy transition” with a focus on the interaction between energy, environment and climate. In this context, the LIED favors a global approach by a unique multi-disciplinary method with researchers working in biology, chemistry, physics, informatics as well as in social sciences. The conversion of solar energy, as defined in this PhD project, as well as its storage are among the LIED research axes.
Pr Aurélie Perrier was appointed full professor in the LIED institute in May 2023. She has been working for 20 years in the field of computational photochemistry, especially in the modeling of the optical properties of photoactive molecules (photoswitches such as DTE and fluorophores) in complex environments (solution, aggregate, within a peptide matrix, grafted on a nanoparticle, within multichromophoric systems) using tools such as TD-DFT, post-Hartree Force calculations and Molecular Dynamics simulations with classical force fields. She has published a series of joint experimental-theoretical works dedicated to DTE, relying on TD-DFT calculations and MD simulations, and articles dedicated to the modeling of the photomechanical motion in PPA using MD simulations. Since 2023, in the LIED institute, she works in the “Climate and energy in urban areas” group and is interested in the in silico design of molecules for the energy storage and conversion. The PhD will work closely with the main supervisor, with a collaboration with an experimental team led by Prof. Stéphane ALOISE (Lille University, France).
Coordonnées de l’équipe:
Laboratoire Interdisciplinaire des Energies de Demain (LIED)
Team “Climate and energy in urban areas”
UMR CNRS 8236 - Bâtiment Lamarck B 6e étage - bureau 601
35 rue Hélène Brion - 75013 Paris
Université Paris Cité
https://u-paris.fr/en/universite-paris-cite/
Secteur: Sciences Physiques et Ingénierie / Physical sciences and Engineering
Langue attendue: Anglais
Niveau de langue attendu: B2
Description
Description du sujet:
Mechanical actuators, like muscles, are materials that can change their own macroscopic shape to perform mechanical work when submitted to external stimuli such as heat, pH, humidity or light. Among these, light is widely used due to its precise and wireless control, spatial selectivity, environmental friendliness, and easy tunability. The resulting photoactuators (PA) can be based on polymer films forming polymeric PA (PPA, Fig.1a). Such materials are usually made of an easily deformable polymer, like a thermoplastic elastomer, in which photoactive molecules, are inserted. The keystones of PPAs are generally organic photochromes such as azobenzene (AZ, Fig. 1b), spyropiran or dithienylethene (DTE, Fig. 1c) derivatives which present large reversible structural modifications due to photoisomerization or photo-cyclization/cycloreversion.
Upon irradiation, PPA films undergo a reversible macroscopic mechanical deformation, which makes these systems interesting for the transduction between (sun)light and mechanical energy, with possible applications in motors, drug delivery devices, textiles or electrical generators. Recent experimental studies have shown that there is a quantitative correlation between the photochromism and the photomechanical effect. Besides, the material structuration is essential at the supramolecular scale (interaction between the photochrome and the neighboring polymer chains) to allow a conversion from the molecular deformation into local material strain and then macroscopic actuation.
Optimization of the PPA properties is still strongly desirable, the time scale associated with the photomechanical effect spanning from minutes to hours, which requires understanding the behavior of these materials at all the relevant scales, including the molecular and supramolecular scales. A that scale, one can use atomistic simulations based on quantum chemistry in order to (1) analyze the mechanical efficiency of the photoswitch and (2) provide molecular understanding of the behavior of the so-called photomorphon, i.e. one photoswitch connected to its neighboring polymer chains.
The first systems studied will be poly(ethylene-co-butylene) matrices doped with two families of photochromes, dithienylethenes (DTE) and azobenzenes (AZ).
- Efficiency of the photoswitch
We can define specifications describing the expected properties of photoswitches with respect to their applications in PPA. Apart from properties such as fatigue resistance and rapid response, the photochromes should present a large structural deformation upon photoisomerisation, and for some applications, a thermal stability. Besides, if one thinks about the “solar mechanical” energy conversion, there should be an overlap between the solar and the photoswitch spectra. A large part of these parameters, when not experimentally accessible, can be provided by atomistic simulations (Density Functional Theory DFT and Time-Dependent DFT).
During this thesis, we will go further by estimating the mechanical efficiency of the photoswitch relying on a mechanochemistry analysis. Indeed, photoswitches convert light into mechanical energy by exerting forces on their environment during photoisomerization. However, the mechanical efficiency of this conversion is limited because a part of the excitation energy can be transferred to internal modes not contributing to the desired switching function: the photoswitch then acts as a local heater and not as a PA. More in details, the PhD student will develop a mechanochemistry tool, based on the analysis of the topology of the low-lying excited states, to calculate the “efficient” mechanical work that a photoswitch can release.
- Properties of the photomorphon
The photomorphon is the unit cell of the photochemical material. The mechanical efficiency of the isolated photoswitch, defined in the first part of the PhD, can indeed be modified by its closest environment: the photoactuation property can be slowed down or even blocked if the interactions with the polymer chains are too strong. At that stage, we aim to get a precise look on the intensity of these interactions during and just after the photoreaction and we will thus use Quantum Mechanics (QM) and Non Adiabatic Molecular Dynamics (NAMD) simulations with model DTE derivatives. We will first determine the topology of the potential energy surfaces PES (static modeling) of isolated molecules in the framework of TD-DFT. Since there is possibly a problem in the description of static correlation effects by TD-DFT, these calculations will be compared with multi-reference calculations. We will then study the photocyclization reaction with NAMD simulations with Tully’s fewest switches algorithm. We will then consider the photomorphon, the DTE model associated with the two neighboring polymer chains and will consider two types of DTE/polymer interactions: Van de Waals, and H bonds We will then follow the strategy developed for the isolated photoswitch to determine the photocyclization path with hybrid Quantum Mechanics / Molecular Mechanics (QM/MM) calculations. The comparison with the isolated molecule will allow us to determine the photoactive properties of the photomorphon, i.e. to what extent the presence of the polymer chains disrupts the photoactive properties of the DTE.
Compétences requises:
We are expecting candidates with a good background in computational chemistry or physical chemistry. The candidate should have a master/academic degree in Physics, Physical Chemistry or Chemistry. She/he should have a good background in physical chemistry and be interested in theoretical chemistry (quantum calculations). She/he must have done a previous research project (Master 1 or Master 2 internship) in molecular modeling, or computational chemistry. We also appreciate candidates with demonstrated publication, but this is not a must. The working language of our group is English and French. A language level of at least B2 in English is desirable.
Références bibliographiques:
(1) Fihey, A.; Perrier, A.; Browne, W. R.; Jacquemin, D. Multiphotochromic Molecular Systems. Chem. Soc. Rev. 2015. https://doi.org/10.1039/C5CS00137D.
(2) Boggio-Pasqua, M.; Perrier, A.; Fihey, A.; Jacquemin, D. Modeling Diarylethene Excited States with Ab Initio Tools: From Model Systems to Large Multimers. In Photon-Working Switches; Yokoyama, Y., Nakatani, K., Eds.; Springer: Tokyo, 2017.
(3) Hamdi, I.; Buntinx, G.; Poizat, O.; Perrier, A.; Le Bras, L.; Delbaere, S.; Barrau, S.; Louati, M.; Takeshita, M.; Tokushige, K.; Takao, M.; Aloïse, S. Excited-State Dynamics of Dithienylethenes Functionalized for Self-Supramolecular Assembly. J. Phys. Chem. A 2018, 122 (14), 3572–3582. https://doi.org/10.1021/acs.jpca.7b10767.
(4) Le Bras, L.; Berthin, R.; Hamdi, I.; Louati, M.; Aloïse, S.; Takeshita, M.; Adamo, C.; Perrier, A. Understanding the Properties of Dithienylethenes Functionalized for Supramolecular Self-Assembly: A Molecular Modeling Study. Phys. Chem. Chem. Phys. 2020, 22 (13), 6942–6952. https://doi.org/10.1039/C9CP06590C.
(5) Le Bras, L.; Lemarchand, C.; Aloïse, S.; Adamo, C.; Pineau, N.; Perrier, A. Modeling Photonastic Materials: A First Computational Study. J. Chem. Theory Comput. 2020, 16 (11), 7017–7032. https://doi.org/10.1021/acs.jctc.0c00762.
(6) Villegas, O.; Serrano Martínez, M.; Le Bras, L.; Ottochian, A.; Pineau, N.; Perrier, A.; Lemarchand, C. A. Mechanical Effect Produced by Photo-Switchable Reactions: Insights from Molecular Simulations. Macromolecular Theory and Simulations 33 (6), 2400033. https://doi.org/10.1002/mats.202400033.
