Tuning the Neutral State Color of Blue, Cyan and Green PI-Conjugated Copolymers By Jointly Playing the Acceptor Strength and the Steric Hindrance
In this presentation we will present the synthesis and characterizations of four pi-conjugated monomers having D-A-D structure (Scheme 1). The donating units are based on a fixed alkylated propylenedioxythiophenes and accepting units based on benzothiadiazole or quinoxaline units bearing variable substituents. The polymerization is conducted under mild conditions via oxidative coupling using iron III trichloride. The obtained copolymers have tunable optical properties that can be relied to the acceptor strength which control of D-A charge transfer (CT). The optical characterizations allow to extract the CIELAB colorimetric coordinates and experimental HOMO-LUMO energetic levels were obtained from electrochemical characterization. We also used computational chemistry (B3LYP and TD-B3LYP methods) to browse the structures of interesting candidates to achieve successful color control in D-A polymers using model compounds (monomers and trimers). Finally a color/structure relationships provides valuable insights on molecular design principles for this class of copolymers, putting forth the importance of jointly playing the steric hindrance factor and the electron-withdrawing/donating strength of carefully chosen substituents.