Synthesis of Single‐Handed Helical Spiro‐Conjugated Ladder Polymers through Quantitative and Chemoselective Cyclizations**

Abstract We report the unprecedented synthesis of one‐handed helical spiro‐conjugated ladder polymers with well‐defined primary and secondary structures, in which the spiro‐linked dibenzo[ a , h ]anthracene fluorophores are arranged in a one‐handed twisting direction, through quantitative and chemoselective acid‐promoted intramolecular cyclizations of random‐coil precursor polymers composed of chiral 1,1′‐spirobiindane and achiral bis[2‐(4‐alkoxyphenyl)ethynyl]phenylene units. Intense circular dichroism (CD) and circularly polarized luminescence (CPL) were observed, whereas the precursor polymers exhibited negligible CD and CPL activities. The introduction of 2,6‐dimethyl substituents on the 4‐alkoxyphenylethynyl pendants is of key importance for this simple, quantitative, and chemoselective cyclization. This strategy is applicable to the defect‐free precise synthesis of other varieties of fully π‐conjugated molecules and coplanar ladder polymers that have not been achieved before.