Investigation of dipole orientation in a side-chain second-order nonlinear optical poly(urethane-imide) by real-time variable temperature FT-IR spectroscopy

The orientation and relaxation of the second-order nonlinear optical (NLO) groups in a side-chain poly(urethane-imide) before and after the electric poling has been investigated with real-time variable temperature FT-IR spectroscopy by monitoring the symmetrical stretching vibration of the nitro group. In situ second harmonic generation (SHG) and ultraviolet-visible (UV–Vis) spectroscopy were also used to compare with the FT-IR results. The results obtained by these techniques are in good agreement with each other.