A new class of push–pull spirobifluorene compounds 1–5 has been synthesized. The nonlinear optical (NLO) properties (first and second hyperpolarizability β and γ, respectively)of spirobifluorene derivatives have been investigated forthe first time using electric field induced second harmonic(EFISH) and third harmonic generation (THG) methods. Moreover, a comparison with the corresponding push–pullfluorene monomers 1a–5a was carried out. Besides the experimental data, ab initio theoretical calculations on structural, electronic, and optical properties were carried out for all compounds. The analyses indicate that an increase in the β and γ values occur on passing from monomers to dimers without compromising the optical transparency.