Distinctive Chiral Conformations Induced to Poly (naphthalene-1,4-diyl) by Helix-sense-selective Polymerization and Circularly Polarized Light Irradiation

Optically active poly(naphthalene-1,4-diyl) was prepared through helix-sense-selective polymerization of the corresponding monomers and also through circularly polarized light (CPL) irradiation, resulting in distinctive circular dichroism (CD) spectral patterns. Chirality of the helix-sense-selective polymerization -based polymer is ascribed to preferred-handed helicity while that of the CPL-based polymer to a non-helical, chiral conformation ('biased-dihedral conformation') with preferred-handedness which was stable only in the solid state. The helix of the helix-sense-selective polymerization-based polymer gradually racemized in tetrahydrofuran while it was stabilized by aggregate formation in a hexane-dichloromethane solution. Both helix-sense-selective polymerization- and CPL-based polymers exhibited efficient circularly polarized luminescence. Non-helical "biased-dihedral conformation" as a novel chiral structure and single-handed helical conformation as one of the well-known, ordered chiral structures are induced to poly (naphthalene-1,4-diyl) by circularly polarized light irradiation and asymmetric polymerization, respectively. The former conformation is stable only in the solid state while the latter resists racemization by aggregation in solution. Both conformations contribute to efficient circularly polarized luminescence. image