Push-pull biphenyl compounds were analyzed, theoretically and experimentally, to correlate the role of twist angle and electronic structure on their linear and nonlinear optical (NLO) properties. Numerical simulations and nuclear magnetic resonance (NMR), infrared (IR) and quadratic NLO response measurements were performed on two analogous biphenyl compounds differing in their zwitterionic character. The IR spectroscopy shows that NLO properties are affected by dielectric environment of the zwitterionic molecules.