Reversible Switching of Strong Light–Matter Coupling Using Spin-Crossover Molecular Materials

• Published in: The journal of physical chemistry letters 2023-08, Vol.14 (30), p.6840-6849
• Main Authors: Zhang, Lijun, Ridier, Karl, Horniichuk, Oleksandr Ye, Calvez, Stéphane, Salmon, Lionel, Molnár, Gábor, Bousseksou, Azzedine
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Coordination chemistry; Optics; Physical Insights into Light Interacting with Matter; Physics
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.3c01136

The formation of hybrid light–matter states through the resonant interaction of confined electromagnetic fields with matter excitations has emerged as a fascinating tool for controlling quantum-mechanical states and then manipulating the functionalities and chemical reactivity landscape of molecular materials. Here we report the first observation of switchable strong light–matter coupling involving bistable spin-crossover molecules. Spectroscopic measurements, supported by transfer-matrix and coupled-oscillator simulations, reveal Rabi splitting values of up to 550 meV, which at 15% of the molecular excitation energy enter the regime of ultrastrong coupling. We find that the thermally induced switching of molecules between their low-spin and high-spin states allows fine control of the light–matter hybridization strength, offering the appealing possibility of reversible switching between the ultrastrong- and weak-coupling regimes within a single photonic structure. Through this work, we show that spin-crossover molecular compounds constitute a promising class of active nanomaterials in the burgeoning context of tunable polaritonic devices and polaritonic chemistry.