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

Abstract

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.

Frontiers in circularly polarized luminescence: molecular design, self-assembly, nanomaterials, and applications

“…Based on the single enantiomer of the chiral Pt(II) complex (R)-55, single-component assemblies with an opposite helical chirality were demonstrated by Zhong and co-workers [200] to exhibit yellow (Φ = 33%-36%, |g lum | = 0.022 at 555 nm) and red (Φ = 25%-27%, |g lum | = 0.027 at 660 nm) AEE CPL, respectively (Figure 17b). Luo and co-workers [201] reported in 2020 the CPL-active liquid crystalline materials based on the chiral Pt(II) complexes (R,S)-56 via straightforward self-assembly. In the high-temperature S m C h * phase, enhanced CPL (Φ = 46%) with a high |g lum | value of 0.04 was detected, induced by effective chirality transfer from the molecule to the liquid crystal assemblies (Figure 17c).…”

“…(b) Chiral Pt complex (R)-55 and the schematic representation of the chirality-inversed assembly [200]. (c) Chiral Pt complexes (R/S)-56 and the CPL properties in different states [201]. (d) Schematic representation of the co-assembly of 57 with (R)-or (S)-58 [202].…”

Supramolecular Assembly and Circularly Polarized Phosphorescence of Tridentate Platinum‐Isocyanide Complexes Modified with a Chiral Leucine Derivative

“…Figure 1a shows some representative platinum(II) complexes ( 1 – 4 ) with CPL activities. Luo and coworkers reported the chiral liquid crystalline platinum complex 1 with a bis‐bidentate configuration, which showed enhanced Φ of 46% and amplified | g lum | of 0.04 at the emission wavelength ( λ em ) of 608 nm in the high‐temperature S m C* phase via liquid crystal self‐organization [10] . Complex 2 is another bis‐bidentate chiral platinum complex with liquid crystalline property [11] .…”

Generating Circularly Polarized Light from Clustering‐Triggered Emission Using Solid Phase Molecular Self-Assembly

“…The glum value, as defined as 2(IL -IR)/(IL + IR), with IL and IR denoting the emission intensities of left-handed CPL (l-CPL) and right-handed CPL (r-CPL) component, respectively 61,62 is -0.016 (Fig. S9), which is comparable to, and even higher than CPL generated from many conventional conjugated organic emitters [63][64][65] . To the best of our knowledge, this is the first CTE based CPL ever reported, indicating it is very promising in creating CPL with green and sustainable materials.…”