(3,9)Carbazolophane - An Effective Chiral Dopant for Achiral Polyfluorene

Abstract

Carbazolophane (Czp) is a well-known, electron-rich paracyclophane (PCP) molecule that allows to introduce planar chirality in organic emitters, notably those displaying thermally activated delayed fluorescence. In an attempt to optimize the preparation of Czp, an alternative synthetic route is explored, following a Suzuki-Cadogan sequence, affording a previously undescribed (3,9)-isomer. The shifted anchoring points give rise to clear structural and spectroscopic differences. The two ( 3,9)Czp enantiomers are successfully resolved and their chiroptical properties are determined in toluene solution. Considering the growing interest in pi-conjugated polymers for circularly polarized optoelectronics, due to their ability to form chiral helical assemblies and thereby realize strong chiroptical activity, (3,9)Czp is then explored as a chiral small-molecule dopant for achiral poly(9,9-dioctylfluorene) (PFO). Polymer films containing 20 wt% of the S p-enantiomer display the strongest chiral amplification (following thermal treatment), reaching a g abs value of 3.0 & times; 10-2.