Helical Network Polymers Exhibiting Circularly Polarized Luminescence with Thermal Stability. Synthesis via Photo-Cross-Link Polymerizations of Methacrylate Derivatives in a Chiral Nematic Liquid Crystal

We synthesized helical network polymers with chiroptical properties through photo-cross-link polymerizations of functionalized methacrylate derivatives in chiral nematic liquid crystals (N*-LCs) used as asymmetric polymerization solvents. Two types of novel methacrylate monomers that contain either a phenylcyclohexyl mesogen-based liquid crystalline moiety or a bis(1,1′-biphenyl)fluorene-luminescent moiety were synthesized. The N*-LCs were prepared by adding axially chiral di- or tetra-substituted ( R )/( S )-binaphthyl derivatives into a host nematic LC (N-LC) mixture containing alkyloxyphenylcyclohexyl and alkylbiphenylcyclohexyl derivatives. Photo-cross-link polymerizations for the mixture of the methacrylate monomers were achieved using a photoinitiator and an additional triacrylate-based cross-linker in the N*-LCs. The helical network polymers showed fingerprint morphologies and even spiral morphologies similar to those of the N*-LCs. Helicities of the helical network polymers were strictly controlled by the chiralities of the N*-LCs. The polymers exhibited not only high quantum yields of approximately 80% but also circularly polarized blue luminescence with thermal stability. It is demonstrated that the photo-cross-link polymerization in the N*-LC is a promising method for creating thermally stable helical network polymers with chiroptical luminescent properties. The present polymers are also anticipated to be applicable for chiral template substances.