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

Abstract

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.

Optical Phenomena in Molecule-Based Magnetic Materials

“…The development of SCO devices, as well as the related systems obtained primarily in bulk or the solution, requires proper characterization techniques, which drove the advances in SQUID magnetometry, 57 Fe Mössbauer spectroscopy, microscopy methods, ultrafast absorption techniques, and others. − Moreover, to rationalize the observed SCO characteristics and to be able to rationally design next-generation systems, a thorough structure–property analysis of a rich library of SCO compounds remains a hot topic in this field. − However, among the basic and most successful methods used to characterize spin-transition materials, the thermal variation of the electronic absorption in the UV–vis region is still a commonly employed technique, which is due to the simplicity of the optical output in terms of possible applications.…”

Constructing Alkyl Chain Modified FeII Spin Crossover Complexes through Complementary Pair Strategy

“…[5] Consequently, Fe II -based SCO materials are believed promisingly in applications of information storage media, display devices, and molecular switches. [6] In pursuit of controlling SCO behavior, a myriad of strategies have been explored, ranging from the application of external physical stimuli such as light, [7] pressure, [8] temperature, [9] and electromagnetic fields, [10] to chemical approaches involving the manipulation of the first coordination sphere, the electronic influence of substituents, [11] the presence of co-crystallized solvent molecules, [12] and the selection of counterions. [13] Despite these advancements, the precise manipulation of transition temperatures and a thorough understanding of the SCO-structural relationship remain critical challenges, underscored by the high sensitivity of SCO properties to environments.…”