Cis-trans isomerization and 13C-NMR chemical shift of polyphenylacetylene

✍ Scribed by Fumiaki Ishii; Shigeyuki Matsunami; Minako Shibata; Toyoji Kakuchi

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 155 KB
• Volume: 37
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19990715)37:14<1657::aid-polb10>3.0.co;2-n

✦ Synopsis

Before and after cis-trans isomerization, the observed 13 C-NMR chemical shifts of poly(phenylacetylene) (PPA) in the solid state were investigated on the basis of 13 C-NMR chemical shift calculations within AM1 for the cis-transoidal and deflected trans-transoidal forms. Two 13 C-resonance peaks in the observed CP/MAS 13 C-spectrum were assigned theoretically by the 13 C chemical shifts of the main and side chains. After thermal isomerization, the 13 C peak of the main chain for PPA shifted upfield by 3.5 ppm, in contrast to the downfield shift of the 13 C peak for polyacetylene. This upfield shift of trans-PPA largely was attributed to the increases of the excitation energy from the ground state to the lowest -* state in the paramagnetic terms of 13 C chemical shift on the main chain carbons with the increase in deflected angle of 0 to 80°. The Ϯ80°deflected conformation of the trans-transoidal chain due to the cis-trans isomerization was confirmed.