Time-resolved studies using FTIR spectrometers: Molecular dynamics at phase transitions

The time-dependent optical properties of molecular systems are investigated by step-scan Fourier-transform spectroscopy to explore the dynamics at phase transitions in the milli-and microsecond range. The electrical switching of liquid crystals traced by vibrational spectroscopy reveals a rotation of the molecules with a relaxation time of 2 ms. The photo-induced neutral-ionic transition in TTF-CA takes place by a suppression of the dimerization in the ionic phase and creation of neutral domains. The relaxation of the spectra follows a stretched-exponential decay with relaxation times in the microsecond range. The electric-field-induced switching in α-(BEDT-TTF)
₂
I
₃
from a low to high-conducting state in the charge-ordered state revealing a temporal response in the infrared spectra pointing towards the excitation of high-mobility charge carriers. We present the experimental setups and discuss the technical challenges.