Reproducible chiroptical activity from aggregated chiral thienopyrroledione–fluorene π‑conjugated polymers

Chiral π‑conjugated polymers have attracted considerable interest because their chiral aggregated structures can generate pronounced chiroptical responses. Here, we report the design, synthesis, and chiroptical characterization of fluorene – thienopyrroledione polymers bearing a single chiral center in each repeating unit, (R)- and (S)-PFTPD, prepared via direct arylation polycondensation to minimize structural defects. Although only weak chiroptical activity was observed in a solution, addition of 1‑butanol to CHCl3 solutions of the polymers induced the formation of stable aggregates that exhibited strong circular dichroism (CD) and circularly polarized luminescence (CPL). Systematic examination of the sample preparation parameters revealed that the mixing process critically influences the chiroptical properties. Dropwise addition of 1-butanol under controlled stirring provided the most reliable results, yielding highly reproducible CD spectra. Under these optimized conditions, the aggregates exhibited an average dissymmetry factor (|gabs|) of 1.5 × 10−2 and a CPL dissymmetry factor (|glum|) of 1.9 × 10−2. These values rank among the highest reported for π-conjugated polymer aggregates bearing only a single chiral source per repeat unit. This study demonstrates that precise control over the solvent-mixing process is essential for the reproducible emergence of chiroptical properties and highlights the chiral TPD unit as a promising platform for chiroptical polymer materials.