Spiro-Conjugated Carbon/Heteroatom-Bridged <i>p</i>-Phenylenevinylenes: Synthesis, Properties, and Microcrystal Electron Crystallographic Analysis of Racemic Solid Solutions
Hiroyoshi Hamada, Takayuki Nakamuro, Keitaro Yamashita, Haruaki Yanagisawa, Osamu Nureki, Masahide Kikkawa, Koji Harano, Rui Shang, Eiichi Nakamura
Abstract
Abstract Two planar conjugated systems perpendicularly connected via a quaternary sp3 carbon center interact with each other through the spiro linkage. Such spiro-conjugated π-systems show useful optoelectronic properties. Herein, we present a unified modular synthetic strategy for a series of chiral spiro-conjugated carbocycles utilizing a C–H activation reaction as a key step. The chiral spiro-conjugated carbon/heteroatom-bridged p-phenylenevinylenes (spiro-X compounds) possessing C, O, N, S, and SO2 as bridging groups are thermally stable, and exhibit circular dichroism and circularly polarized luminescence (CPL). Spiro-SO2 undergoes intramolecular charge transfer. It exhibits CPL with a large |glum| of 2.1 × 10−3 and shows rarely reported solvatofluorochromism for CPL luminophores. The racemic spiro-O compound solidifies as a racemic solid solution (or pseudoracemate). It did not form X-ray-quality crystals. This therefore provided us with a unique opportunity to examine the potential of the microcrystal electron crystallography popularized recently. The diffraction data sets, merged over many micrometer-sized solid particles, afforded the 3D molecular structure and the crystal packing of the spiro compound.