Periodic Reporting for period 4 - MMUSCLES (Modification of Molecular structure Under Strong Coupling to confined Light modES)
Reporting period: 2021-10-01 to 2023-03-31
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 presence of nanophotonic structures allows to change the properties of light so fundamentally that this change is noticeable to the molecules even when there is no external light at all, and only the field generated by the molecules themselves is present. 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 system is described by hybrid light-matter states, so-called polaritons, that share and combine aspects of 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.
The main conclusions of the project have been that molecular polaritonics do indeed provide a range of novel strategies to manipulate molecular properties and obtain novel functionalities, not just in photochemistry, but in a wide range of additional aspects, such as light absorption and emission characteristics, energy transport over long distances and/or different molecular species. The field has grown and evolved over the last years, new design principles have been developed, and several active efforts exist to develop competitive devices (such as organic light emitting diodes) going beyond the state of the art.
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.
The main conclusions of the project have been that molecular polaritonics do indeed provide a range of novel strategies to manipulate molecular properties and obtain novel functionalities, not just in photochemistry, but in a wide range of additional aspects, such as light absorption and emission characteristics, energy transport over long distances and/or different molecular species. The field has grown and evolved over the last years, new design principles have been developed, and several active efforts exist to develop competitive devices (such as organic light emitting diodes) going beyond the state of the art.
During the project, we made significant progress along the overarching goal of understanding and exploiting modifications of molecular structure induced by strong light-matter coupling. This research has attracted increasing interest, and has led to the development of the fields 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 arising in strongly coupled molecule-cavity systems.
The main objectives followed two overarching lines: increasing the microscopic complexity of 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 these lines and opened several new ones.
We developed numerically advanced methods capable of treating such systems in significantly more detail than previously possible. These include a tensor-network approach for simulating the full quantum dynamics of several molecules in complex nanophotonic structures for hundreds or even thousands of atoms making up the molecules, as well as of the continuum of light modes supported by the nanophotonic structures, while staying numerically tractable even on a normal desktop computer. In a complementary development, we extended the methods of molecular dynamics simulations to include the description of quantized cavity modes, allowing for semiclassical simulations describing large numbers of molecules that can undergo arbitrary chemical reactions, and exploits state-of-the-art approaches for treating multiscale molecular dynamics by interfacing with quantum chemistry codes. Additionally, 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. By combining the general theory we developed 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). Finally, we developed a method to obtain a description of the quantized electromagnetic field in the presence of arbitrary nanophotonic structures while using a minimal number of photon modes to do so. This method has opened up the way to fully include the details of complex nanophotonic setups in relatively simple quantum models, and the application and extension of these concepts to several systems and situations of interest is one of the current main research lines in the group.
The methodological and theoretical developments described above laid the groundwork for improving our understanding of strongly coupled light-matter systems, and many of the main physical results obtained within the project have relied on these methods. To name just a few, we (together with several different collaborators) have shown how singlet fission could be improved inside a cavity (see attached image), how a careful selection of the relative energetics of polaritons and bare-molecule states allows the funnelling of energy from a large number of molecules to a small subset, how intersystem crossing in molecules is affected by polariton formation, or how the frequency spectrum of broadband solar absorbers can be tailored by polariton formation.
All of the results discussed above have been published in leading journals, presented in a wide range of international conferences and workshops. We are also participating in several projects working towards practical applications of some of the concepts described above.
The main objectives followed two overarching lines: increasing the microscopic complexity of 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 these lines and opened several new ones.
We developed numerically advanced methods capable of treating such systems in significantly more detail than previously possible. These include a tensor-network approach for simulating the full quantum dynamics of several molecules in complex nanophotonic structures for hundreds or even thousands of atoms making up the molecules, as well as of the continuum of light modes supported by the nanophotonic structures, while staying numerically tractable even on a normal desktop computer. In a complementary development, we extended the methods of molecular dynamics simulations to include the description of quantized cavity modes, allowing for semiclassical simulations describing large numbers of molecules that can undergo arbitrary chemical reactions, and exploits state-of-the-art approaches for treating multiscale molecular dynamics by interfacing with quantum chemistry codes. Additionally, 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. By combining the general theory we developed 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). Finally, we developed a method to obtain a description of the quantized electromagnetic field in the presence of arbitrary nanophotonic structures while using a minimal number of photon modes to do so. This method has opened up the way to fully include the details of complex nanophotonic setups in relatively simple quantum models, and the application and extension of these concepts to several systems and situations of interest is one of the current main research lines in the group.
The methodological and theoretical developments described above laid the groundwork for improving our understanding of strongly coupled light-matter systems, and many of the main physical results obtained within the project have relied on these methods. To name just a few, we (together with several different collaborators) have shown how singlet fission could be improved inside a cavity (see attached image), how a careful selection of the relative energetics of polaritons and bare-molecule states allows the funnelling of energy from a large number of molecules to a small subset, how intersystem crossing in molecules is affected by polariton formation, or how the frequency spectrum of broadband solar absorbers can be tailored by polariton formation.
All of the results discussed above have been published in leading journals, presented in a wide range of international conferences and workshops. We are also participating in several projects working towards practical applications of some of the concepts described above.
The novel methods developed during this project (see above) have extended 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 were able to use them in collaboration with various experimental groups to interpret and guide experimental studies and develop new strategies for enhancing molecular functionalities. Furthermore, over the last few years many of the concepts developed in the context of molecular systems have started to be applied to more varied targets, such as 2D materials, superconductors, or ferromagnets, with cavities potentially providing a novel control knob. We thus expect that there will be a continued and steady stream of results based on the concepts, methods, and applications developed in the project.