High Efficiency Luminescent Liquid Crystalline Polymers Based on Aggregation-Induced Emission and “Jacketing” Effect: Design, Synthesis, Photophysical Property, and Phase Structure

Abstract

A series of high efficiency luminescent liquid crystalline polymers (LLCPs) based on aggregation-induced emission (AIE) and the "Jacketing" effect, namely, poly{2,5-bis{[2-(4-oxytetraphenylethylene)-n-alkyl]oxycarbonyl}styrene} (denoted as Pm, m = 2, 4, 6, 8, 10, 12), were successfully designed and synthesized via introducing tetraphenylethylene to the side group with different length spacers. Because of the AIE effect, the resultant LLCPs are completely free of aggregation caused quenching. The photophysical properties and phase behavior were studied via various techniques such as UV−vis absorption spectra, photoluminescence spectra (PL), polarized light microscopy (PLM), differential scanning calorimetry (DSC), and variable temperature one-dimensional wide-angle X-ray diffraction (1D WAXD). The results revealed that the resultant monomers showed typical AIE behavior and the polymers exhibited aggregation enhanced emission (AEE) behavior. Moreover, due to the "Jacketing" effect, the polymers showed high efficiency luminescence in the liquid crystalline state, which was significantly dependent on the spacer length (the solid-state quantum yields decreased from 52% to 18% with increasing spacer length). Meanwhile, the glass transition temperatures (T g ) decreased with increasing the length of spacers. With increasing the spacer length, the phase structure transformed from smectic A (SmA) (Pms, m = 2, 4, 6) to hexagonal columnar phase (Col H ) (Pms, m = 8, 10, 12). All the polymers presented good filmforming property and processing performance, which made them be promising materials for the luminescent devices.

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

“…Surprisingly, a contrary behavior concerning the emission properties, particularly the PLQY, was observed. Here, an increase in the spacer length yielded an increase in the fluorescence quantum yields, which is contrary to the results of Tang [ 27 ] and Xie, [ 28 ] who found a decrease of PLQY upon an increase of the spacer length for polymers containing TPE‐luminophores, which was attributed to a higher degree of freedom of the TPE moieties. For CST‐14 and CST‐15 , however, the increase of PLQY by increasing spacer lengths was explained by the more effective stacking of the CST moieties into J‐ aggregates and subsequently a stronger fluorescence due to the restriction of motion.…”

“…obtained a series of polystyrene‐based polymers with two TPE units attached to the side chain ( TPE‐15 ) (Figure 12). [ 28 ] The polymers were strongly luminescence in the mesophase as well as in the solid state.…”

“…(A) Molecular structure of the polymeric TPE mesogens ( TPE‐14 , 15 , and 16 ) and (B) schematic representation of the smectic and columnar structure of TPE‐15 with varying spacer lengths. Adapted and reproduced with permission from the American Chemical Society, copyright 2017 [ 28 ] …”

Stimuli-Sensitive Aggregation-Induced Emission of Organogelators Containing Mesogenic Au(I) Complexes

“…AIE is usually observed in rigid solids like crystals; however, several groups have also reported the occurrence of AIE phenomena in soft condensed phases, e.g., liquid crystal (LC) phases [31,32], noncrystalline polymers [33,34], and so on [35,36]. In particular, LC gold complexes have been reported to show changes in emission behavior through phase transitions [37,38].…”

A stabilized lamellar liquid crystalline phase with aggregation-induced emission features based on pyrrolopyrrole derivatives

“…The published AIE-LC research works mainly focused on employing TPE as AIE-active cores. 5,6,9,11,[27][28][29][30][31] Fewer other kinds of AIE units have been adopted to synthesize AIE-LC compounds. 14,[32][33][34][35] In this paper, we constructed AIE-LCs based on the AIEgens of 1,2,4,5-tetraphenyl-1,4-dihydropyrrolo[3,2-b]-pyrrole (TPPP) developed by our groups.…”