Supramolecular Chirality in Achiral Polyfluorene: Chiral Gelation, Memory of Chirality, and Chiral Sensing Property

Producing supramolecular chirality from achiral pi-conjugated polymers toward preferred chiral memory, effective circularly polarized luminescence, and chiral sensor is extremely important in design of functional chiral materials. Proposed herein is an effective protocol to generate and memorize the supramolecular chirality formed from achiral poly(9,9-dioctylfluorene) (PF8) induced by chiral solvation. The process of chiral supramolecular assembly. was monitored by UV-vis spectroscopy, circular dichroism (CD), and fluorescent spectroscopy. Achiral PF8 dissolved in neat (R)(+)-limonene (1R) and (S)-(-)-limonene (1S) underwent chiral sol-gel transition at -20 degrees C. PF8 aggregates revealed intense CD and circularly polarized luminescence (CPL) signals due to beta-phase, exhibiting absolute dissymmetry ratio of approximate to 2 X 10(-3) at 430-470 nm. The supramolecular chirality of PF8 aggregates can be perfectly memorized in solid film even near decomposition temperature (300 degrees C), comparing favorably with that from chiral polyfluorene. Atomic force microscopy (AFM) inferred helically distorted PF8 aggregate motifs responsible for the CD and CPL functionality. Furthermore, the first chiral sensor to detect nonracemic limonene molecules employing achiral PF8 spin-cast film from CHCl3 solution was achieved.