Quadratic electro-optic effect in the nonconjugated conductive polymer iodine-doped trans-polyisoprene, an organic nanometallic system

Thin films of 1,4-trans-polyisoprene have been prepared on various substrates from toluene solution and characterized using Fourier transform infrared (FTIR) spectroscopy, optical absorption spectroscopy and X-ray diffraction before and after doping with iodine. The optical absorption spectrum at low doping shows two peaks: one at 4.2 eV and the other at 3.2 eV. X-ray diffraction indicates an increase of (111) and (122) peak intensities upon doping. Quadratic electro-optic measurements have been made using field-induced birefringence. The Kerr coefficients as measured (3.5×10⁻¹⁰ m/V ² at 633 nm and 2.5×10⁻¹⁰ m/V ² at 1.55 μm) are exceptionally large, and they have been attributed to the subnanometer-size metallic domains formed upon doping and charge transfer.