Enhanced Synchronously Emission Dissymmetry Factor and Quantum Efficiency of Circularly Polarized Phosphorescence from Point-Chiral Cyclometalated Platinum(II) Liquid Crystal

Circularly polarized luminescence (CPL) derived from supramolecular self-assembly chirality has been a fascinating field of research due to its applications in photoactive devices and bioactive probes. Herein, we report a straightforward pathway for the construction of efficient chirality transfer and enhanced circularly polarized phosphorescence based on platinum(II) metallomesogens via liquid crystal self-organization. Overall, two chiral metallomesogens, the enantiomeric complexes of ( S )-Pt-L1 and ( R )-Pt-L1, were obtained based on the combination of the rodlike achiral phenylpyridine and point-chiral pyridinic acid derivatives. Experiments with polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and variable-temperature X-ray diffraction show that there are two smectic phases during cooling and heating processes, namely the high temperature S m C* and low temperature S m C phases, and the S m C h * phase. Interestingly, the circular dichroism (CD) and circularly polarized luminescence (CPL) tests reveal that the chirality transfer from the molecule to liquid crystal self-organization does occur indeed in the high temperature S m C* and S m C h * phases. However, both the CD and CPL signals are silent in the low temperature S m C phase, even in the solution, suggesting that chirality transfer depends on the self-organization superstructure of the liquid crystal. Moreover, the dissymmetry factor (| g lum | = 4.0 × 10 –2 ) in the high temperature S m C* phase is 1–2 orders of magnitude higher than that of Pt(II) complexes previously reported. Also, the elevated photoluminescence quantum yield (Φ PL = 0.46) is obtained for the liquid crystal film, indicating that the enhanced CPL properties can be achieved through self-organization of mesomorphic organoplatinum molecules. Another interesting observation is made that the racemic mixture (( S )-Pt-L1 and ( R )-Pt-L1) shows spontaneous chirality separation in the high temperature S m C 1 phase.