Electroabsorption of a new urethane-substituted polydiacetylene PDA-5BCMU-4A in a film

An excitonic band with a vibronic sideband shows linear and quadratic Stark shifts in a film of a new polydiacetylene with π-conjugation between polymer backbone and substituents, i.e. PDA-5BCMU-4A (polymer from 6,8,10,12-octadecatetraynylene bis-(N-butoxycarbonylmethylcarbamate)), revealing differences in the polarizability Δα = 780 e Å2/V and the static dipole moment Δμ = 29 debye between the ground and excitonic states. The electroabsorption peak at 2.23 eV is attributed to a band-to-band transition. The maximum absolute values of the real and imaginary parts of the nonlinear susceptibility near the excitonic transition are 1.4 × 10−9 and 2.9 × 10−9 esu, respectively. These results are explained in terms of the higher order due to the planarity of the polymer backbone and side chains in this material.