Highly Efficient Luminescent Liquid Crystal with Aggregation-Induced Energy Transfer

Abstract

A luminescent liquid crystal molecule (TPEMes) with efficient solid-state emission is rationally constructed via the chemical conjugation of blue-emitting tetraphenylethene cores and luminescent mesogenic tolane moieties, which are both featured with aggregation-induced emission properties. As for this fluorophore, aggregation-induced energy transfer from the emissive tolane mesogens to the lighting-up tetraphenylethene units endows the molecule pure blue emission in the suspension and bulk state. Combining differential scanning calorimetry, polarized optical microscope, and one-dimensional X-ray diffraction (1D XRD) experiments, the compound TPEMes is deduced to adapt thermodynamically more stable layered crystalline phase and can be “frozen” into a monotropic smectic mesophase due to kinetic reasons. As a result of more dense packing of TPEMes in the crystalline phase indicated by 1D XRD, the luminescence of TPEMes in crystalline phase blue-shifted by 17 nm relative to the metastable mesophase.

From simple Katritzky salts to AIEgens: mechanochromic luminescence and heparin detection

“…The cationic fluorophores could be purified by simple filtration or flash column chromatography with a high yield of around 60%. The chemical identities of these novel luminogens were unambiguously confirmed by 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy. Mass spectra (Fig.…”

“…Fortunately, a large family of luminogens featuring aggregation-induced emission (AIE) properties, 10,11 which usually exhibit bright emission in aggregated or solid states, have been discovered and extensively explored in the past two decades. The typical AIE-active fluorophores, such as tetraphenylethene (TPE), 12,13 are usually structurally featured with propeller-shaped and sterically congested geometry. The free intramolecular motions including the rotation and vibration of the AIE luminogens (AIEgens) will non-radiatively dissipate the excited-state energy and lead to low photoluminescence (PL) quantum yields.…”

Mesogens with aggregation‐induced emission properties: Materials with a bright future

“…The Tang group synthesized a monosubstituted TPE derivative combining the blue emission of the TPE core with the luminescent mesogenic TOL unit showing a monotropic smectic phase (Figure 8). [ 20 ] The temperature‐depending luminescence of TPE‐9 showed a blue‐shift of 17 nm in the emission wavelength upon cooling from the metastable mesophase to the crystalline state, which was attributed to the denser packing of the TPE cores in the latter.…”

“…(A) Molecular structure of a monosubstituted tetraphenylethene tolane mesogen ( TPE‐9 ) and (B) pseudo‐focal‐conic‐fan shaped texture of TPE‐9 observed via POM upon cooling from 180 to 40°C and (C) spherulitic texture of TPE‐9 upon heating from 40 to 100°C. Adapted and reproduced with permission from the American Chemical Society, copyright 2019 [ 20 ] …”

Mesogens with Aggregation-Induced Emission Formed by Hydrogen Bonding

“…Within the past decades, fluorescent LCs are receiving increasing attention, since the combination of the ability to emit light and spontaneously self-assemble into mesoscopic structures is promising for optoelectronic applications, such as anisotropic light-emitting diodes and emissive liquid crystal displays. − Depending on the molecular alignment in the mesophase (nematic or chiral-nematic), fluorescent LCs may emit linear or circular polarized light. However, a major problem in the development of novel fluorescent liquid crystals is that, typically, the fluorescence emission is dramatically reduced during the formation of the ordered phase (mesophase or crystalline state). , This challenge can be overcome by the use of aggregation-induced emission (AIE) chromophores. − These chromophores exhibit a rotorlike structure, allowing high rotational mobility in organic solvents, converting absorbed light into motion and a resultant loss in emission. However, upon aggregation, intramolecular motion (RIM) or intramolecular rotation (RIR) is restricted, triggering fluorescence or phosphorescence emission.…”