Poly(phenylacetylene) with bulky chiral germyl groups: Synthesis and effects of measuring solvents and temperature on chiroptical properties

(+)-p-[{Methyl(1-naphthyl)phenyl}germyl]phenylacetylene, an acetylene with a bulky chiral germyl group, was polymerized with [(nbd)RhCl]₂-Et₃N to give a high-molecular-weight polymer in good yield. The CD spectrum of the polymer exhibited very large molar ellipticities [θ] in the UV region in non-aromatic solvents (e.g. THF and CHCl₃). In contrast, the CD signals of the polymer in aromatic solvents (e.g. toluene, tetralin, and benzene) became appreciably smaller: [θ]_max = 6.4 × 10⁴ (330 nm) and -4.7 × 10^4o cm² dmol^-1 (370 nm) in CHCl₃; [θ]_max = 1.1 × 10⁴ (330 nm) and -0.7 × 10^4o cm² dmol^-1 (370 nm) in toluene. The [θ]_max values of the polymer in aromatic solvents increased when the solutions were heated, which is attributed to decreased π-π interaction between the solvents and side groups.