Two classes of aryltrienes in which the conjugation was incorporated in six-membered rings have been developed. The microscopic nonlinear susceptibility, mubeta, the product of the dipole moment and the second-order nonlinear susceptibility, of these chromophores were measured using electric field-induced second harmonic generation (EFISH). The chromophores were then copolymerized as side-chain pendant groups in a methacrylate backbone copolymer with methyl methacrylate and their macroscopic electrooptic coefficients, r, were experimentally determined using a reflection technique after electric field poling of the polymers. When compared with 4,4’-NN-dimethylaminonitrostibene (DANS), these molecules demonstrated electrooptic activities up to three times of DANS, when measured at 1.3 mum. By using a simple two-level free-gas model, the two sets of measurements corresponded closely at low poling fields. At high fields, the simple model breaks down as more detailed poling parameters are required to accurately describe the nonlinear poling effects. The results of the analysis of the high-field poling data will be published separately.