Second-Order Nonlinear Optical Effects in Novel Polymethacrylates Containing a Molecular-Ionic Chromophore in the Side Chain

We have synthesized new glassy methacrylate polymers containing a molecular-ionic (N-methylpyridinium) nonlinear optical chromophore in the side chain. A bulky tetraphenylborate (TPB) counterion was substituted at the salt unit in order to reduce the migration of the counterion during the process of poling. It was found that the poling-induced chromophore alignment of the TPB-containing polymer is significantly improved compared to that of the iodide or bromide containing polymers. The second-order nonlinear optical susceptibility, ϰ⁽²⁾(−2ω;ω,ω), of the poled TPB-containing polymer is approximately 5 times larger than that of the corresponding iodide analogue. Also, the temporal stability of the poled structure of the TPB-containing polymer is found to be considerably improved over that of the analogous iodide containing polymer.