Clear Disclosure of Hierarchical Chirality Transfer Mechanism and Wide Full‐Color and White‐Light CPL Emissions with Both High g_lum and Intensity by TPE Helicates

Abstract

in 3D displaying, biological imaging, information processing and storing, asymmetric catalysis, and so on. [1][2][3][4][5][6][7] However, the two key indices for assessment of CPL performance, dissymmetric factor (g lum ), and quantum yield are still low. Especially the reported g lum value is generally between 10 −5 and 10 −2 , which is much smaller than theoretical value 2. Chirality transfer is a general strategy for enhancing dissymmetry in research of chiral materials such as chiral switches, chiral recognition agents, asymmetric catalysts, and so on. [8][9][10] For boosting the CPL g lum values of chiral fluorophores, chirality transfer and amplification are frequently exploited. [10][11][12][13][14] For example, chiral additives have been doped into achiral liquid crystals (LC) to induce chirality of LC [15] and significantly enhance the CPL signals [16] by chirality transfer from the chiral dopant to LC. The chiral dopants generally possess central and axial chirality, and contain some group such as long alkyl chains that are similar to those of LC molecule for increasing miscibility. [17][18][19][20][21] However, up to now helical chirality is not used in LC probably due to the molecular shape that is considered not to be compatible with that of LC molecules although of a large number of molecules with helical chirality such as helicenes. [22] By using the chiral additives, very impressive large CPL g lum value that is more than 1 can be obtained in LC, [20][21] but the fluorescence quantum yield is still low. Moreover, how the chirality is transferred to the achiral LC molecules is unknown considering that the disclosure of chirality transfer mechanism is still a challenge. [23][24] In some systems, transient CD and CPL spectra need to be used in demonstrating the chirality transfer. [25][26] Aggregation-induced emission (AIE) molecules are a new class of fluorophores that are especially suitable for using as solid emitter such as CPL active materials. [27][28][29][30][31][32][33] In a bunch of AIE molecules, tetraphenylethylene (TPE) and their derivatives are most extensively studied because of easy synthesis, facile modification, and stable AIE effect. [28,[33][34] After the propeller-like conformation of TPE unit was fixed through cyclization between phenyl rings, the obtained TPE helicates (TPEH) not only emit Chirality transfer and amplification play key role on research of chiral materials, but it is still a challenge to clearly disclose the chirality transfer mechanism. Here, tetraphenylethylene helicate (TPEH) with aggregation-induced emission enhancement effect is doped into achiral nematic liquid crystal (NLC) to furnish a system of excellent chirality transfer and amplification for the first time. It is found that left-handed helical (M) TPEH molecule with four phenyl rings sloping right-down makes a staggered overlap with other M-TPEH at right-up direction for attenuating the repulsive force between phenyl rings, which is further overlapped into a right-handed helix (P) and then drives NLC a...

Asymmetric Synthesis of Tetraphenylethylene Helicates and Their Full-Color CPL Emission with High glum and High Fluorescence Quantum Yield

“…In fact, the huge Cotton effect was ascribed to the helical phase of 5CB which had a positive signal due to the right-handed supramolecular helical arrangement and the negative one was resulted from the left-handed helical phase according to our previous research. 16 As demonstrated in Figure 7, very strong CPL signals at 403 nm for M/P-1-5CB, M/P-2-5CB, and M/P-3-5CB appeared. This CPL signal increased with the TPE helicate fraction, and the increasing trend was not stopped until the TPE helicates were not further dissolved in 5CB.…”

“…However, the CD signals of these chiral addictive dyes were too weak to be observed. In fact, the huge Cotton effect was ascribed to the helical phase of 5CB which had a positive signal due to the right-handed supramolecular helical arrangement and the negative one was resulted from the left-handed helical phase according to our previous research …”

“…Therefore, the magnified CPL signals should come from supra-helical self-assembly of the TPE helicates which induce the LC molecules to form helical phase with the same helical direction. In the same way as we previously reported, , when the single-handed rod-like tetracycle tetramine helicate was doped into achiral nematic liquid crystal (NLC), left-handed helical (M) TPE helicate tend to form a staggered overlap with other M-TPE in a right-handed helical direction due to the steric adaptability between phenyl rings of the overlapping TPE units, which impelled NLC array layers to form the P-LC phase. As a result, M-TPE helicate generated the P-LC phase and P-helicate furnished the M-LC phase.…”

“…This result indicated that the TPE helicate composed of (S)-diamine bridge was M-configuration, while the (R)-diamine bridge led to P-enantiomer, which was in consistent with the previous reports and was also in line with the crystal structure. 16 From 430 to 250 nm, there were bisignate bands that came from the excitation coupling of the adjacent phenyl rings, indicating the helical structure of the TPE unit (Figure 5A−C). Not only in solution but also in suspension and film states, they displayed similar CD signals as well (Figure S50).…”

Intense Circularly Polarized Fluorescence and Room-Temperature Phosphorescence in Carbon Dots/Chiral Helical Polymer Composite Films

“…Circularly polarized luminescent (CPL) materials, as emerging advanced chiroptical functional materials, are drawing enormous attention in multidisciplinary fields − owing to their significant potential applications in three-dimensional displays, optical identification sensors, spintronics, optical storage devices, and bioimaging, etc. − Among various CPL materials, circularly polarized room-temperature phosphorescence (CPRTP) materials featuring long afterglow represent an emerging research frontier and exhibit promising applications in various fields. − Chirality and luminescence are two prerequisites for the generation of CPL emission. In view of the striking advancements concerning RTP C-dots, theoretically, CPRTP-active C-dots may be realized by reasonably introducing the chiral factor.…”