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Updated: May 23, 2026

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional π-conjugate Systems
Published on: February 10, 2020
Pressure Tuning of the Low-Frequency Raman Response in Spin-Crossover Networks
Guanping Li1,2, Olaf Stefanczyk2, Joseph M Flitcroft1
1Department of Chemistry, University of Manchester, Manchester M13 9PL, U.K.
Abstract:
Stimuli-responsive molecular materials that show low-frequency (LF) terahertz (THz) responses are promising candidates for molecular switches and sensors in next-generation photonic technologies. In this work, we report two novel compounds, thermally activated spin-crossover (SCO) material {[Fe(pyridine)2][Hg(SCN)3]2}n (1) and paramagnetic {[Fe(pyridine)2][Hg(SCN)4]}n (2), obtained by selectively controlling the precursor ratios. Pressure-dependent crystallographic, magnetic and Raman spectroscopic studies confirm pressure-induced SCO from high-spin to low-spin Fe(II) at room temperature and ∼1 GPa of pressure. The Raman-active modes in both compounds display substantial blue shifts under compression, with maximum pressure sensitivities reaching 7.89 cm-1/GPa near 240 cm-1, and with the additional observation of a low-energy mode in 1 that shows an unusual red shift through the pressure-induced SCO. Angle-dependent Raman measurements in the LF, fingerprint and C≡N stretching regions of the spectrum also show strong polarization sensitivity. First-principles modeling of the IR- and Raman-active phonon modes in both ambient and high-pressure structures reliably reproduces the THz absorption and angle-dependent Raman spectra, allowing assignment of the spectral features to the underlying atomic motion. This work establishes pressure tuning of the LF phonon modes and spin states in molecular SCO materials as a novel approach to modulating THz light and hence provides new avenues for the design of tunable THz absorbers for advanced photonics applications.
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