Chiroptical generation and amplification of hyperbranched π-conjugated polymers in aggregation states driven by limonene chirality

In this contribution, a series of hyperbranched pi-conjugated poly(9,9-di-n-octylfluorene)s (HPF8s) with hexaoctyltruxene (HT) as branching units were successfully prepared by a Suzuki polycondensation reaction. We present the first generation of optically active HPF8s in aggregation states with strong circular dichroism (CD) and circularly polarised luminescence (CPL) properties. The optically active aggregates of HPF8s were efficiently produced by CD-/CPL-silent HPF8s with the help of solvent chirality transfer from chiral limonene at room temperature. The emergence of CD and CPL signals of HPF8s aggregates results from the weak forces (pi/pi, van der Waals, CH/pi and OH/pi interactions) in a tersolvent system of chloroform (a good solvent), alkanol (a poor solvent), and (R)-(+)-/(S)-(-)-limonene (1R/1S, a chiral source). The hyperbranched polymer structure (degree of branching), poor solvent type, volume fraction of methanol and 1R/1S, limonene enantiopurity and polymer concentration have obvious effects on the magnitude and sign of the CD signals. The obtained HPF8s aggregates have relatively strong UV-vis absorption and CD signals in the range of 300-500 nm as well as CPL emission (420-460 nm) under optimised conditions. The current study will open up a new avenue for efficiently producing ambidextrous chiroptical hyperbranched polymeric materials without any specific chiral catalysts or substituents under mild conditions.