Ladderization: A Powerful Strategy for Controlling Supramolecular Helical Ordering, Amplifying Asymmetry, and Emerging and Enhancing Circularly Polarized Luminescence

We report the synthesis of optically-active pi-conjugated coplanar ladder polymers with enantiopure side groups that enable helical ordering-induced circular dichroism (CD) and circularly polarized luminescence (CPL) in a specific solvent mixture and in the film state, whereas the corresponding linear polymer precursor showed a negligible CD and CPL in any state, demonstrating the key role of the coplanar ladder framework in forming well-ordered supramolecular chiral aggregates. The CPL activities of the pristine films of the chiral ladder polymers were significantly enhanced after solvent vapor exposure, leading to a luminescence dissymmetry factor exceeding 0.1, which arises from the more ordered helical aggregation. This methodology for enhancing the CPL was versatile and highly effective in generating a comparably intense CPL even when the films contained up to 75 mol% of an achiral analogue of the chiral ladder polymer, demonstrating strong amplification of the asymmetry. Furthermore, the CPL color of the film could be readily tuned by Förster resonance energy transfer to an achiral ladder polymer with a backbone structure different from that of the chiral ladder polymer.