Development of a Spacerless Flow-Cell Cavity for Vibrational Polaritons

Abstract

We developed a spacerless flow-cell cavity for the observation of vibrational strong coupling and demonstrate its availability in two samples with a CN bond: a metal complex (aq) and an ionic liquid. It is shown that the cavity length can be tuned over a wide range to investigate coupling with different order Fabry-Pérot cavity modes without reassembling the cavity. In the ionic liquid, analyses based on the coupled harmonic oscillator model with multiple vibrational modes show that the Rabi splitting parameters and the square root of the integrated absorption intensity are proportional among the three neighboring vibrational modes. Our spacerless cell structure simplifies the comparison of the different vibrational strong coupling measurements, such as the mode order dependence and the coupling to different molecular vibrations.

Influence of Vibrational Strong Coupling on an Ordered Liquid Crystal

“…Only recently has optical mode coupling to vibrational transitions, called vibrational polaritons, been achieved. − Vibrational polaritons have attracted considerable attention among chemists because of recent reports of reaction rate modification − and altered product branching ratios. , Formation of vibrational polaritons may make it possible to systematically modulate the molecular potential energy landscape and adjust reaction pathways, opening up an entirely new way to control chemical kinetics. However, much remains to be solved concerning the mechanisms underlying chemical reactivity under strong coupling; experimental results are puzzling and sometimes prove difficult to replicate. , The role of the uncoupled dark state reservoir is unclear, yet it is believed to play an important role in vibrational polariton dynamics. , Theoretical approaches have been proposed by several groups, but they are as yet unsuccessful in fully explaining the reaction rate modulation. − …”

Ultrafast Spectroscopy under Vibrational Strong Coupling in Diphenylphosphoryl Azide

“…One example is the ionic liquid, EMIMDCA, for which we have reported a Rabi splitting of ∼180 cm −1 for the 1 mode. 9 To model the transient spectrum shown in Figure 3c, we estimate the fraction of molecules that are excited by the pump pulse by comparing the positions of the LP and UP peaks in the pump-off versus pump-on spectra. For the ∼0.3 M sample, we found a reduction of ∼1% in the Rabi splitting.…”

“…These polariton modes are energetically separated by Rabi splitting, ℏ Ω R . Vibrational polaritons are a kind of polariton composed of infrared-active vibrational transitions and cavity photons. − Following the pioneering works by Ebbesen et al, , vibrational strong coupling (VSC) is now recognized as a new tool to modulate the vibrational potential energy surface in the electronic ground state, allowing for systematic modification of chemical reactivity and manipulation of bulk material properties by the formation of delocalized collective states. − A number of groups have reported exciting results, including reaction selectivity, ,, increased ionic conductivity, enhanced driving of DNA origami coassembly, and acceleration and suppression of ground-state reactivity. , Despite continued reports of modified molecular properties and chemical reactivity, the mechanisms behind them have still not been clearly elucidated. One major unsolved problem is, for example, the relation between the coherent and delocalized nature of the vibrational polaritons and the modified properties of VSC systems.…”

Optical Cavity Design and Functionality for Molecular Strong Coupling

“…Even at a temperature of 3 K, a cryogenic FP cavity with piezoelectric Ref. [63] with permission from American Chemical Society.) actuators can operate.…”

“…c) Sectional view of the spacerless FP cavity. (Reproduced fromRef [63]. with permission from American Chemical Society.…”