Synthetic Control of the Excited‐State Dynamics and Circularly Polarized Luminescence of Fluorescent “Push–Pull” Tetrathia[9]helicenes

A series of fluorescent “push‐pull” tetrathia[9]helicenes based on quinoxaline (acceptor) fused with tetrathia[9]helicene (donor) derivatives was synthesized for control of the excited‐state dynamics and circularly polarized luminescence (CPL) properties. In this work, introduction of a quinoxaline onto the tetrathia[9]helicene skeleton induced the “push–pull” character, which was enhanced by further introduction of an electron‐releasing Me 2 N group or an electron‐withdrawing NC group onto the quinoxaline unit (denoted as Me 2 N‐QTTH and NC‐QTTH, respectively). These trends were successfully discussed in terms of by electrochemical measurements and density functional theory (DFT) calculations. As a consequence, significant enhancements in the fluorescence quantum yields ( Φ FL ) were achieved. In particular, the maximum Φ FL of Me 2 N‐QTTH was 0.43 in benzene (NC‐QTTH: Φ FL =0.30), which is more than 20 times larger than that of a pristine tetrathia[9]helicene (denoted as TTH; Φ FL =0.02). These enhancements were also explained by kinetic discussion of the excited‐state dynamics such as fluorescence and intersystem crossing (ISC) pathways. Such significant enhancements of the Φ FL values thus enabled us to show the excellent CPL properties. The value of anisotropy factor g CPL (normalized difference in emission of right‐handed and left‐handed circularly polarized light) was estimated to be 3.0×10 −3 for NC‐QTTH.