Yongrong Li

Sequential double click reactions: a highly efficient post-functionalization method for optoelectronic polymers

A new post-functionalization method based on the Huisgens 1,3-dipolar cycloaddition between azides and alkynes, followed by the atom-economic addition reaction between electron-rich alkynes and tetracyanoethylene (TCNE) was developed to introduce the donor–acceptor chromophores into polystyrene derivatives in remarkably high yields.

Novel design of organic donor–acceptor dyes without carboxylic acid anchoring groups for dye-sensitized solar cells

Organic donor–acceptor dyes, formed by a high-yielding [2 + 2] cycloaddition–retroelectrocyclisation process between aniline-substituted alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), were employed as novel photosensitizers without carboxylic acid anchoring groups in dye-sensitized solar cells (DSSCs). The efficient adsorption of the donor–acceptor dyes onto TiO2 was confirmed by UV-vis and IR spectroscopies. The photovoltaic performances of the DSSCs suggested that the triphenylamine derivatives 3 and 4 provide higher current densities (Jsc) as compared to the corresponding dimethylaniline counter molecules 1 and 2. This was mainly due to the excellent charge-separation efficiencies and lower charge-recombination rates of the triphenylamine moieties. It was also found that the devices sensitized by the TCNQ-adducted dyes 2 and 4 display open-circuit voltages (Voc) higher than those of the TCNE-adducted counter dyes 1 and 3. All these results were reasonably explained by the J–V curve fitting based on the equivalent-circuit model as well as the comparison between the absorption and incident-photon-to-current-conversion efficiency (IPCE) spectra.

A Novel Polymeric Chemosensor: Dual Colorimetric Detection of Metal Ions Through Click Synthesis

A highly colored polystyrene derivative bearing side chain chromophores composed of dialkylanilino donor and cyano-based acceptor groups, prepared by atom-economic click postfunctionalization, displays the dual colorimetric detection behavior of several metal ions based on the specific interactions with different nitrogen atoms. Hard to borderline metal ions, such as Fe(3+) , Fe(2+) , and Sn(2+) , are always recognized by the dialkylanilino nitrogen atom, resulting in a decrease in the charge-transfer (CT) band intensity of the donor-acceptor chromophores. On the other hand, the recognition site of a soft metal ion of Ag(+) is the cyano nitrogen atom due to the readily formed multivalent coordination, which produces a bathochromic shift of the CT band.

Colorimetric sensing of cations and anions by clicked polystyrenes bearing side chain donor–acceptor chromophores

Donor–acceptor chromophores were introduced into the side chains of a polystyrene derivative through the efficient click postfunctional addition reaction between dialkylaniline-activated alkynes and small acceptors, such as tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). The resulting polystyrenes were fully characterized by GPC, 1H NMR, IR spectroscopy, and elemental analysis. After the postfunctionalization, the polymers were highly colored due to the formed donor–acceptor chromophores in the side chains and these chromophores showed a colorimetric sensing behavior for some metal ions and anions. Some hard-to-borderline metal ions were always recognized by the dialkylanilino nitrogen atom, resulting in a decrease in the charge-transfer (CT) band intensity of the donor–acceptor chromophores. However, the recognition site of the soft Ag+ ion was the cyano nitrogen atoms due to readily formed multivalent coordination, leading to a bathochromic shift in the CT bands for both TCNE- and TCNQ-adducted polymers. This remarkable dual colorimetric detection of two different types of metal ions was achieved by the elegant design of polymeric chemosensors. On the other hand, it was found that the dicyanoethene moieties of the side chain chromophores serve as a chemodosimeter for some anions. For example, the CN− ion underwent a nucleophilic addition reaction to the electron-deficient ethene moieties, resulting in a dramatic decrease in the CT bands. All types of sensing behavior of both cations and anions were visually recognized. The use of small molecular model compounds enabled the estimation of the kinetic parameters and the product structures.

Multi-coloration of polyurethane derivatives through click postfunctionalization, electrochemical oxidation, and Ag+ ion complexation

A colorless polyurethane derivative bearing electron-rich alkynes substituted by the dialkylaniline donors at both sides was prepared by polyaddition between a diol monomer and tolylene-2,4-diisocyanate. Click chemistry-type postfunctionalization of this polyurethane was accomplished by a [2 + 2] cycloaddition followed by retro-cyclization with the electron-accepting tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), yielding new orange or green colored polyurethane derivatives with the intramolecular charge-transfer (CT) band centered at 476 and 698 nm in CH2Cl2, respectively. These polymers were comprehensively characterized by GPC, 1H NMR and IR spectroscopies, and elemental analysis. Despite its sufficient thermal stability, the precursor polyurethane was readily oxidized in air under mild heating conditions. Inspired by this result, the electrochemical oxidation of the precursor polyurethane was performed. Application of potentials higher than the first oxidation potential of 0.25 V (vs. Ag/AgCl) reasonably produced the blue colored aromatic amine-based cation radical. Although the cyclic voltammogram of the polyurethane films was irreversible, the blue color was almost persistent under an inert atmosphere. The colors of the postfunctionalized polyurethanes were further changed by Ag+ ion complexation with cyano groups, which modulated the strengths of the intramolecular donor–acceptor interactions. Thus, the solution color of the TCNE-adducted polyurethane changed to magenta and that of the TCNQ-adducted polyurethane to a yellowish-green upon the Ag+ ion addition. The plots in the 1976L*a*b* color space revealed the production processes of each color.

Origin of Second-Order Nonlinear Optical Effects of Nonpoled Donor–Acceptor Chromophores on Surface

Thin films of alkyl conjugated donor–acceptor (D–A) molecules, prepared by a high-yielding addition reaction between electron-rich alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), were investigated by ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopy, in-plane and out-of-plane X-ray diffraction (XRD), and second-harmonic generation (SHG) measurements. The variable self-assembling ability of D–A chromophores produced different molecular orientations in the thin films. The TCNQ-adducted D–A molecule formed a centrosymmetric bilayer structure based on the strong interactions between the chromophores, while the film of the TCNE-adducted counter molecule was composed of interdigitated alkyl layers and randomly oriented chromophores due to their weak interactions. The interfacial interactions between a substrate and a TCNE-adducted molecular layer were expected to induce a noncentrosymmetric chromophore orientation in the thin film, which produced an effective SHG coefficient (deff) of ca. 21 pm V-1 without electric poling.