<p>Poly(phenylacetylene)s (PPAs) are one kind of important helical polymers with tunable main chain conformations. However, the preparation of near-infrared optically active helical PPAs remains a challenge. Here, we report a novel helical poly(<i>m</i>-terphenyl acetylene)s (PTPAs) bearing two chiral alkylamide pendants, which showed a stretched <i>cis-transoid</i> helix in solution or poly(methyl methacrylate) matrix with a broad optical activity range from the ultraviolet-visible (UV-Vis) to near-infrared regions. The effects of substituents, solvents, temperature, and acid/base additions on the helical conformation were carefully investigated. The substituent structure had little effect on the elongation but remarkably affected the main chain screw sense. The stability of this extended <i>cis-transoid</i> helix depends on the solvent applied and the temperature. Reversible conformational transitions between the one-handed <i>cis-transoid</i> helices and frustrated coil conformations can be achieved by the addition of trifluoroacetic acid and triethylamine. Furthermore, full-color circularly polarized luminescent materials can be prepared by virtue of their broad Cotton effects and chirality-selective absorption.</p>