| To systematically understand the structure and property relationships and development of zwitterionic chromphores and non linear optical (NLO) polymers for applications in organic electro-optic (EO) materials and near infrared (NIR) fluorescent sensing, two series of zwitterionic chromphores, FDCNs (dicyanomethane-based) and PpQDMs (tricyanoquino-dimethane-based) and their corresponding NLO polymers were designed and synthesized. Incorporation of bulky groups onto the central part of FDCN chromophore was demonstrated as an effective strategy to minimize dipole-dipole molecular interaction. Efficient conjugated bridges were extended from dipyridylium donors and coupled with very strong 3CNQ electron acceptors to afford PpQDM chromophores with very large dipole moments and high hyperpolarizabilities. X-ray crystallographic data, negative solvatochromism, IR and NMR analysis confirm the charge-separated ground states of these two series of zwitterionic chromophores.;Thirdly, the poling conditions were optimized through investigations into various factors such as the molecular shape of the chromophores, the polarity of host polymers, poling voltage, and temperature. A large EO coefficient of 70 pm/V at the telecommunication wavelength of 1550 nm has been obtained with a 5 wt % PpQDM-Ben doped PVP polymer using an in situ poling technique. A buffer layer (PEDOT: PSS/PVA) was first introduced into the double layer EO device, and improvement of the poling efficiency of NLO polymer systems was demonstrated.;Furthermore, PpQDMs are NIR fluorescent with large Stokes shifts and show high microenvironmental (pH, solvent polarity) sensitivity. PpQDM-Met (M1) is capable of selectively detecting metal ions (Fe 2+, Cu2+) signaled by changes in the absorption and fluorescence. M1/copper complex was prepared and demonstrated to be the first high-contrast colorimetric and NIR fluorescence turn-on molecular probe for sensitive and selective detection of cysteine.;In addition, FDCN-MMA NLO polymers (NA2) were synthesized, in which the chromophore contents reached 14 wt % and exhibited high solubility, thermal stability and film-forming ability. PpQDM-based crosslinkable NLO polyimides were prepared through grafting the hydroxyl-containing PpQDM and BCBO crosslinking unit onto an acid-containing polyimide host. High chromophore loading (13.8 wt %) onto the polyimide was obtained. The Tg values of NLO polyimides were observed to vary due to different pendant groups and different PpQDM loading levels. |
