Stereoregular polymerization of (p-3-methylbutoxy)phenylacetylene (p3MBPA) was successfully performed with a [Rh(NBD)Cl](2) catalyst to afford poly(p-3-methylbutoxy)phenylacetylene (Pp3MBPA) having a cis-transoid form in high yields when ethanol or l-butanol in the presence of triethylamine was used as the polymerization solvent. The resulting cis polymer was composed of a pseudohexagonal structure called columnar as x-conjugated self-assembly or Jr-conjugated self-organization in the solid state. The columnar polymer underwent isomerization from the predominant cis to trans form when compressed at 100 kg/cm(2) at room temperature. The pristine polymer and the compressed polymer were characterized in detail using H-1 NMR, wide-angle X-ray diffraction, laser Raman, electron spin resonance, and diffuse reflective UV-vis methods. Consequently, the data showed that the absorption maximum of the pi -conjugated columnar polymer appears in an extremely longer wavelength region, i.e., at 490 nm, despite the cis form compared with 450 nm of the amorphous cis form. In the solid state, a large blue shift of the absorption maximum was found to be induced when the columnar structure was destroyed by compression to produce a trans-transoid form which has planar zigzag pi -conjugation sequences. The pristine columnar polymer showed the lambda (max) as an entire absorption at notably longer wavelength so that the chromophore of the pi -conjugated columnar polymer is not to be simply attributed to the primary structure, e.g., a repeated double-single bond structure, but rather should be ascribed to that of aggregated molecules called the pi -conjugated columnar as self-assembly or self-organization. This explanation is a new concept with respect to the color of pi -conjugated columnar polymers and is very important for the molecular design of electroluminescense (EL) and nonlinear optical (NLO) materials which are used at present in the solid state.