Field-stimulated electrooptics in quinoline and stilbene chromophore derivatives incorporated into photopolymer thin films

Abstract

Optically and electric-field induced linear electrooptics effect (PILEOE) was discovered during investigations of the 3-(4-Nitrophenyl)-6-N,N-diphenylamine-1-phenyl-1H-pyrazolo[3,4-b]quinoline and stilbene chromophores embedded into polymer PMMA matrices. The PILEOE was discovered in the quinoline and stilbene derivatives incorporated into the polymer PMMA matrices. one can see that the PILEOE coefficients achieve their maxima after 130–140 s of the bicolor photo-treatment with simultaneous applied electric field. For the both polarization geometries corresponding to two different electrode-laser polarizations the maximal value of the PILEOE coefficient is achieved for the two pyrazoloquinoline molecule and lower Pockels effect is achieved for the stilbene molecule. The behavior is changed drastically for cross-polarized (electrode-pump polarizations). In this case the effect is very low for pyrazoloquinoline chromophore (A and B) and is substantially larger for the C chromophore. Moreover, the absolute value of the achieved PILEOE is almost the same for co- and cross-polarized experimental geometry. The performed molecular geometry optimization and quantum chemical simulation have shown that the observed features are different for the two class of the chromophore and by different influence of external bicolor light on the photo-structural changes. For the quinoline crucial role belongs to co-planar nitrogen atoms, which are very sensitive to the geometry of photoinduced electrooptics effect. For the case of the stilbene role of the cis–trans isomerization is not so crucial and the corresponding anisotropy is almost absent contrary to the generally adopted model. For all the investigated chromophore maximal values of the PILEOE effect is smaller in the direction perpendicular the pump polarization (cross-polarized geometry) compared to the parallel (co-polarized) ones. The anisotropy is substantially larger for the quinoline chromophore compared to the stilbene ones. Analysis of photoinduced optical absorption and IR spectra of quinoline show principal role of the nitrogen-induced co-planarity inside the aromatic groups in the observed PILEOE anisotropy.