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 SmC* and low temperature SmC phases,
and the SmCh* 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 SmC* and SmCh* phases. However, both the CD and CPL signals
are silent in the low temperature SmC 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 SmC* phase is 1–2 orders
of magnitude higher than that of Pt(II) complexes previously reported.
Also, the elevated photoluminescence quantum yield (ΦPL = 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 SmC1 phase.