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 pi-conjugation be tween polymer backbone and substituents, i.e. PDA-5BCMU-4A (polymer fr om 6,8,10,12-octadecatetraynylene bis-(N-butoxycarbonylmethylcarbamate )),revealing differences in the polarizability Delta alpha = 780 e Ang strom(2)/V and the static dipole moment Delta mu = 29 debye between th e ground and excitonic states, The electroabsorption peak at 2.23 eV i s 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 x 10(-9) and 2.9 x 10(-9) esu, respec tively. These results are explained in terms of the higher order due t o the planarity of the polymer backbone and side chains in this materi al.