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 −4.7×104° cm2 dmol−1 (370 nm) in CHCl3; [θ]max=1.1×104 (330 nm) and −0.7×104° 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.