Xinyan Su

Thermally stable oxadiazole-containing polyacetylenes: Relationship between molecular structure and nonlinear optical properties

Two novel high molecular weight functional polyacetylenes bearing oxadiazole groups as pendants, poly(2-(4-decyloxyphenyl)-5-(4-ethynylphenyl)-1, 3, 4-oxadiazole) (P1) and poly(2-(4-butyloxyphenyl)-5-(4-ethynylphenyl)-1, 3, 4-oxadiazole) (P2) were designed and synthesized by a multistep reaction route. The structures and properties were characterized and evaluated with FTIR, NMR, UV, TGA, GPC, optical-limiting (OL) and nonlinear optical (NLO) analyses. The incorporation of oxadiazole into polyacetylene significantly endows polyacetylenes with higher thermal stability and optical limiting property. The solubility, stereoregularity and optical properties of resultant polyacetylenes are obviously affected by flexible terminal alkoxy chain length. The cis olefinic structure content in polyacetylene backbone increases with increasing terminal alkoxy group length. The functional polyacetylene with the higher cis olefinic structure content shows higher thermal stability, better optical limiting property and larger third-order nonlinear optical performance. The optical limiting mechanism of resulting polymers was investigated, which is mainly originated from larger excitation state absorption cross-section of molecules to result in reverse saturable absorption.

Supramolecular self-assembly structures and properties of zwitterionic squaraine molecules

To further investigate the influence of H-bond combining with π–π stack interaction on the optical performances, a few rigid zwitterionic squaraine molecules, with different terminal H-bond recognition abilities, are identified and designed. They can controllably construct a series of supramolecular self-assemblies with different morphologies and dimensions via a simple solution-based self-assembly method under mild conditions. The morphologies, synergetic reinforcing effect, and optical-thermal properties are investigated and confirmed by both theoretical and experimental methods. The results indicate that the morphologies of the resultant self-assemblies can be effectively controlled by rational molecular design, whose absorption and emission spectra and thermal stabilities accordingly change with the alteration of zwitterionic squaraine molecular structures.

Investigation of optical nonlinearities and transient dynamics in a stilbenzene derivative.

The temporal properties of nonlinear absorption of a stilbenzene derivative have been investigated by time-resolved pump-probe techniques with picosecond laser pulses at the wavelength of 532 nm. With the help of an additional nanosecond and picosecond open-aperture Z-scan technique, numerical simulations based on a new five-energy level model are used to interpret the experimental results, and the nonlinear optical parameters of this new compound are determined. The five-energy level model is described by two-photon absorption (TPA) excited from ground-state-induced excited-state absorption (ESA) including singlet ESA and triplet ESA. Under the nanosecond pulse excitation, a TPA excited from the triplet excited state contributes to the nonlinear absorption, and the value of the TPA is found to be 1 order of magnitude larger than those usually found for TPA excited from the ground state.

Preparation and properties of electron injecting molecular hybrid materials with high thermal performance

A series of oxadiazole-containing molecular hybrid materials with different structures (H1–H5) are controllably prepared by a hydrosilylation method based on the octahydridosilsesquioxane (POSS, T88HH). All these resultant hybrid materials are soluble in common organic solvents, such as chloroform, toluene, tetrahydrofuran, and 1,2-dichloroethane, and possess good film-forming properties. Their structure and properties are characterized and evaluated by FTIR, 1H NMR, 29Si NMR, GPC, TGA, DSC, UV-vis, PL, CV, and elemental analysis, respectively. It is found that the hydrosilylation reaction almost proceeds quantitatively when the feed ratio (molar number of organic monomer to molar number of POSS) is less than 4, at which the resultant hybrids can be controllably prepared by varying the feed ratio. These hybrids possess high thermal stability and good electron injecting properties and an intense blue emission was observed in these hybrids. Simultaneously, it is found that the hybrids (H3–H5) with a strong π electron conjugation effect between POSS and the oxadiazole moiety show higher thermal stability, better electron injecting properties and more intense blue emission than those (H1 and H2) without a π electron conjugation effect between POSS and the oxadiazole moiety.

Preparation and Optical Limiting Properties of Polyurethane Containing Long Conjugated Chromophores

Two functional polyurethanes (P1 and P2) bearing a large π electron conjugated chromophoric pendant were synthesized and characterized by FT‐IR, 1H‐NMR and UV‐Vis absorption spectra. Their optical limiting properties were evaluated. The results show that P1 and P2 show novel optical limiting properties, which are assigned to a long π electron conjugated chromophoric pendant. It was found that their optical limiting properties were affected simultaneously by solution concentration and P2 displays a better optical limiting property than P1 at the same solution transmittance, although that P1 has larger χ(3) (4.28×10−11 esu) than P2 (0.87×10−11 esu), and their optical limiting mechanism is investigated.

Fabrication of flexible conductive graphene thin films based on high water-soluble sulfonated-triazine non-covalent functionalized graphene

We report a facile and scalable fabrication of flexible conductive graphene thin films via a vacuum filtration method based on high water-soluble sulfonated-triazine non-covalent functionalized graphene colloid (STGNS). A novel sulfonated triazine (ST) molecule was synthesized using a one-step method to improve the dispersion stability of graphene during the chemical reduction. AFM image of STGNS sheets showed the STGNS is individual dispersion of graphene sheets in water. FTIR, and UV-vis revealed ST molecules were successfully loaded onto graphene sheets by hydrogen bonding anchoring and π–π stacking. It was found that the dark homogeneous suspension of the STGNS with concentration up to 4.5 mg mL-1 can remain stable with no visible precipitate for more than 6 months. The high watersoluble individually dispersed graphene colloid facilitated large-scale fabrication of flexible conductive graphene films with different thickness by adjusting the content of STGNS. The obtained graphene films exhibited a sheet resistance as low as ca. 5.6 KΩ-1 with 78% transparency at 550 nm.