title: Propeller Chirality of Boron Heptaaryldipyrromethene: Unprecedented Supramolecular Dimerization and Chiroptical Properties.
abstract: Chiral boron dipyrromethenes (BPs) enjoy high fluorescence efficiency at visible to near-IR wavelength regions with a reasonable range of dissymmetry factors. Here, we demonstrate that the (quasi)propeller chirality, similarly to hexagonal propeller in hexaarylbenzene, can be effectively induced in heptaarylated BP. In addition, supramolecular dimer was formed at low temperatures in nonpolar solvent, which exhibits strong bisignate Cotton effects at BP transitions (the couplet amplitude A = 193 M-1cm-1) in the circular dichroism (CD). Due to the bulky substituents on the propeller blades, but with void space around boron atoms, BP chromophores in the dimer are aligned in a head-to-tail manner with a small torsion (φ ≈ 15°), to avoid fluorescence quenching usually observed in H-type dimer of BPs, exhibiting strong circularly polarized luminescence (CPL) signals (glum= 2.0 × 10-3, Φlum= 0.45). Such supramolecular dimer formation would be viewed as an alternative approach for designing and developing novel chiroptical materials.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Osaka University , 2-1 Yamada-oka, Suita, Osaka, 565-0871, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Toyoda
authors.affiliation: Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University , 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan.
authors.forename: Yoshitane
authors.initials: Y
authors.lastname: Imai
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Osaka University , 2-1 Yamada-oka, Suita, Osaka, 565-0871, Japan.
authors.forename: Tadashi
authors.identifier: http://orcid.org/0000-0003-3918-0873
authors.initials: T
authors.lastname: Mori