Photoconductive films of poly-N-vinylindole-based blends for high-voltage photorefractive electrooptic cells

In the frame of our research on the electrooptic behavior of poly-N-vinylindole (PVI) and a series of its methyl derivatives, we have measured the photoconductivity of poly-2,3-dimethyl-N-vinylindole (PV2,3DMI) at room temperature. The measurements have been accomplished on 100 mum-thick films obtained by squeezing the polymer between two ITO sheets at about 130 degreesC. The electrooptic cell was introduced in a dc electric circuit, and a voltage up to 15,000 V could be applied between the ITO sheets while irradiating at lambda = 685 nm and at a power of the order of 10 mW with a laser diode. Very special care had to be taken in order to allow the use of such high voltages, like for instance a thermal treatment at about 150 degreesC of the sample held under vacuum during a few minutes. The measured photoconductivity of PV2,3DMI was higher than that of PVI but lower than that of poly-N-vinylcarbazole (PVK). The result obtained for PV2,3DMI confirms the anticipated positive effect of the two methyl groups in lowering the ionization potential of the N-alkylindole. PV2,3DMI has shown a good compatibility with a NLO molecule, giving very transparent and stable films for photorefractivity tests. A two-beam coupling (2BC) electrooptic circuit for photorefractivity measurements has been built and tested with PVK blends. (C) 2003 Elsevier Science B.V. All rights reserved.