Preparation of polymer films containing multi-branched chromophores for enhanced nonlinear optical activity

Two new multi-branched chromophores were synthesized via esterification from monochromophores to achieve ideal macroscopic nonlinear optical activities. Molecular chemical structures of chromophores were confirmed by 1H NMR, FT-IR spectroscopy, elemental analysis, mass spectrometry and UV-visible absorption spectra. Monochromophore N1 and bichromophore DN were doped into poly (4-vinylphenol) to fabricate guest-host polymer films Film-N1 and Film-DN with high molecular loading density (up to 30 wt%). And the maximum second harmonic generation coefficients (d33) of polymer films Film-N1 and Film-DN reached to 25 pm V−1 and 39 pm V−1, respectively. In contrast, six-branched dendritic chromophore SN was utilized directly to prepare thin film Film-SN without any polymer matrix due to its large molecular weight (about 3183 Da) and the d33 value of Film-SN was up to 208 pm V−1. Compared with Film-N1, films containing multi-branched chromophores Film-DN and Film-SN exhibited about 1.6-fold and 8.3-fold enhancement in the d33 value indicating the multi-branched chromophore could significantly promote the macroscopic optical nonlinearity through the site-isolation effect.