Origin of the Color of π-Conjugated Polymers: Poly(N-n-octyl-3-carbazoyl)acetylene Prepared with a [Rh(norbornadiene)Cl]2 Catalyst

Abstract

Stereoregular polymerization of (N-n-octyl-3-carbazoyl)acetylene was successfully performed with a [Rh(NBD)Cl]2 (NBD = norbornadiene) catalyst to afford poly(N-n-octyl-3-carbazoyl)acetylene (PNOCzA) as a new type of possible electron-transporting polymer in fairly high yields when triethylamine, chloroform, or dimethylformamide was used as the polymerization solvent. The resulting polymers were composed of amorphous cis−transoid isomers bearing a yellow color or crystalline cis−transoid isomers having an orange color, called a columnar, as a π-conjugated molecular assembly at the solid state. The cis-to-trans isomorization of the yellow and orange polymers was induced by compression at 200 kg/cm2 under vacuum at room temperature for 10 min. The polymers obtained before and after compression were characterized in detail using 1H NMR, wide-angle X-ray diffraction, laser Raman, electron spin resonance, and diffuse reflective UV−vis (DRUV−vis) methods. The data showed that compression of the orange polymers r...