Double Click Synthesis and Second-Order Nonlinearities of Polystyrenes Bearing Donor−Acceptor Chromophores

Abstract

Donor−acceptor chromophores were almost quantitatively introduced into the side chains of a polystyrene derivative by sequential “click chemistry”-type addition reactions as an efficient postfunctionalization method. The first click reaction is the conventional Cu(I)-catalyzed azide−alkyne cycloaddition (CuAAC), and the second one is the atom-economic addition of strong acceptor molecules, such as tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), to the aniline-substituted electron-rich alkynes. Steric hindrance was found to be an important factor in determining the reactivity of alkyne-acceptor addition reactions. All obtained polymers showed good solubility in common organic solvents, and they were fully characterized by GPC, 1H NMR and IR spectroscopy, and elemental analysis. After the acceptor addition, the polymers showed an intense charge-transfer (CT) band centered at ca. 480 nm for the TCNE adducts and ca. 710 nm for the TCNQ adducts. Electrochemical measurements of these polymers also revealed well-defined oxidation and reduction potentials, offering consistency between the electrochemical and optical band gaps. The second harmonic generation (SHG) coefficients (d33 and d15) of the polymer thin films were evaluated by SHG measurements before and after corona poling at 150 °C, a temperature that was determined on the basis of thermal analyses. The results show that the TCNE adducted polymers possess better SHG properties than the corresponding TCNQ adducted polymers, probably reflecting the superior chromophore mobility within the polymers.