Periodic Reporting for period 3 - MMUSCLES (Modification of Molecular structure Under Strong Coupling to confined Light modES)
Periodo di rendicontazione: 2020-04-01 al 2021-09-30
The project MMUSCLES – Modification of Molecular Structure Under Strong Coupling to Confined Light Modes – is focused on what we now call polaritonic chemistry and/or molecular polaritonics, i.e. the modification and manipulation of molecular properties due to their interaction with light modes in nanophotonic cavities. Light, or electromagnetic waves, are one of the best tools we have for manipulating matter, for example by using lasers. However, the advances of nanophotonics nowadays allow to change the “tracks” on which light moves so fundamentally that this change is noticeable even when there is no light at all. In this regime of “strong coupling”, the molecular quantum states are mixed with the states of light and it becomes impossible to treat them separately. Instead, the states in the system become hybrid light-matter states, so-called polaritons, that share aspects from both their constituents. In the last years, it has become clear that these changes also affect the internal structure of the molecules and their dynamics, which paves the way towards using this effect to change material properties and even chemical reactions. For example, this could provide a completely novel way of catalysing reactions, in particular photochemical reactions for which very few conventional catalysts exist, but which are of paramount importance for, e.g. harvesting light energy with organic solar cells. MMUSCLES is focused on developing theoretical methods capable of treating these fundamentally quantum effects and using them to explain and develop this new way of doing chemistry and manipulating materials.
Importantly, the coupling strengths available in these systems are so large that important quantum effects are expected and observed even at room temperature, also opening the route towards possible room-temperature quantum devices.
Importantly, the coupling strengths available in these systems are so large that important quantum effects are expected and observed even at room temperature, also opening the route towards possible room-temperature quantum devices.
Over the current period, we have made significant progress along the overarching goal to develop and apply the appropriate theoretical methods to study and predict strong-light-matter-coupling-induced modifications of molecular structure. This research has attracted increasing interest over the last years, and has led to the development of the blossoming field we now call polaritonic chemistry and molecular polaritonics, summarizing the dual ideas of modifying both chemical reactions and electromagnetic properties through the formation of polaritons, the hybrid light-matter excitations that describe the coupled molecule-cavity system in the strong-coupling regime.
The main objectives of the action follow two overarching lines: increasing the microscopic complexity taken into account in the molecular models, and increasing the macroscopic complexity induced by the typically large number of involved molecules and photonic modes. We have made steady progress along both of these lines. In the context of solar energy storage using organic molecules, we showed that it is possible to use the properties of polaritons to change molecular structure in such a way that a single photon can start off a chain reaction that can release all the stored energy (see attached image). This effect exploits the collective nature of the interaction between a light mode and many molecules, which opens new reaction pathways that are not available in traditional chemistry.
We have also developed several methods going beyond the state of the art in describing various aspect of the light-matter coupling. The first is a tensor-network approach that allows to perform a fully quantum simulation of the complex dynamics of several molecules in complex nanophotonic structures. This requires simulating the motion of the hundreds or thousands of atoms making up the molecules as well as the response of all the light modes (in principle, infinitely many of them) that are supported by the nanophotonic structures. This approach exploits some fundamental properties of the systems we treat to reduce the size of the problem from something that could not be solved on any existing or future supercomputer using a “naïve” approach to a calculation taking a few weeks on a normal desktop computer.
The second method we developed is applicable for larger numbers of molecules that undergo arbitrary chemical reactions, and exploits state-of-the-art approaches for treating multiscale molecular dynamics in biochemistry. In particular, we combined the theoretical approaches of quantum optics with these well-known methods from quantum chemistry, which allow taking into account all the details of molecular structure.
Finally, we developed a fundamental theory of how chemical reactivity of a molecule in its electronic ground state is affected within nanocavities when there is no external input of energy. These ground-state chemical reactions (as opposed to light-driven photochemical reactions) determine a large fraction of chemistry in everyday life. We developed a novel theoretical framework that combines quantum electrodynamics and the quantum theory of chemical reactivity to treat this problem. This allowed to explore the general properties of cavity-induced ground-state chemical reactivity changes and develop a simplified theoretical model that can be applied to more complex molecules. By combining this fundamental theory with quantum chemistry calculations, we could show how plasmonic (metallic) nanocavities can enable self-induced electrostatic catalysis of typical organic reactions, without any external driving, due to the interaction of the molecular permanent and fluctuating dipole moments with the plasmonic cavity modes (see sketch in the attached image). We also explored how the interaction between molecules and electromagnetic modes can modify the transition temperature of spin-crossover transition metal complexes, the prime example of molecular switches.
The main objectives of the action follow two overarching lines: increasing the microscopic complexity taken into account in the molecular models, and increasing the macroscopic complexity induced by the typically large number of involved molecules and photonic modes. We have made steady progress along both of these lines. In the context of solar energy storage using organic molecules, we showed that it is possible to use the properties of polaritons to change molecular structure in such a way that a single photon can start off a chain reaction that can release all the stored energy (see attached image). This effect exploits the collective nature of the interaction between a light mode and many molecules, which opens new reaction pathways that are not available in traditional chemistry.
We have also developed several methods going beyond the state of the art in describing various aspect of the light-matter coupling. The first is a tensor-network approach that allows to perform a fully quantum simulation of the complex dynamics of several molecules in complex nanophotonic structures. This requires simulating the motion of the hundreds or thousands of atoms making up the molecules as well as the response of all the light modes (in principle, infinitely many of them) that are supported by the nanophotonic structures. This approach exploits some fundamental properties of the systems we treat to reduce the size of the problem from something that could not be solved on any existing or future supercomputer using a “naïve” approach to a calculation taking a few weeks on a normal desktop computer.
The second method we developed is applicable for larger numbers of molecules that undergo arbitrary chemical reactions, and exploits state-of-the-art approaches for treating multiscale molecular dynamics in biochemistry. In particular, we combined the theoretical approaches of quantum optics with these well-known methods from quantum chemistry, which allow taking into account all the details of molecular structure.
Finally, we developed a fundamental theory of how chemical reactivity of a molecule in its electronic ground state is affected within nanocavities when there is no external input of energy. These ground-state chemical reactions (as opposed to light-driven photochemical reactions) determine a large fraction of chemistry in everyday life. We developed a novel theoretical framework that combines quantum electrodynamics and the quantum theory of chemical reactivity to treat this problem. This allowed to explore the general properties of cavity-induced ground-state chemical reactivity changes and develop a simplified theoretical model that can be applied to more complex molecules. By combining this fundamental theory with quantum chemistry calculations, we could show how plasmonic (metallic) nanocavities can enable self-induced electrostatic catalysis of typical organic reactions, without any external driving, due to the interaction of the molecular permanent and fluctuating dipole moments with the plasmonic cavity modes (see sketch in the attached image). We also explored how the interaction between molecules and electromagnetic modes can modify the transition temperature of spin-crossover transition metal complexes, the prime example of molecular switches.
The novel methods developed during this project (see above) extend the state of the art and now provide a rich toolbox to treat various problems of interest, in addition to the results obtained up to now. In particular, we are now in contact with various experimental groups to interpret and guide experimental studies. We thus expect several results along the lines discussed above over the next few years, in particular on the topics of guiding photochemical reactions and observing quantum effects at room temperature.