A Joint Experimental and Theoretical Investigation on Nonlinear Optical (NLO) Properties of a New Class of Push-Pull Spirobifluorene Compounds

A new class of push-pull spirobifluorene compounds 1-5 has been synthesized. The nonlinear optical (NLO) properties (first and second hyperpolarizability beta and gamma, respectively) of spirobifluorene derivatives have been investigated for the first time using electric field induced second harmonic (EFISH) and third harmonic generation (THG) methods. Moreover, a comparison with the corresponding push-pull fluorene 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 beta and gamma values occur on passing from monomers to dimers without compromising the optical transparency.