Ionic liquid crystals with aggregation-induced emission properties based on pyrrolo[3,2-b]pyrrole salt compounds

Abstract

The emission behaviors of AIE–ILC molecules (DPP-2Py-9) in different aggregation states were affected by their molecular stacking arrangements.

Functional Ionic Liquid Crystals

“…Due to the change in aggregation mode at various temperatures, the ILC showed temperature-dependent fluorescence. 155 On the basis of a similar mechanism, Ren et al reported ILCs with temperature-dependent fluorescence, which was composed of 1:4 supramolecular complexes of four carboxylate-bearing tetraphenylethenes and dimethyldioctadecylammonium which exhibited an LC phase with a helical column that packed in a monoclinic lattice. 156,157 To change the fluorescence profiles of ILCs with an AIE nature, not only a temperature change but also various external stimuli are applicable.…”

Current Topics in Ionic Liquid Crystals

“…An important tool to classify these interactions are the so‐called Hofmeister series of cations and anions (also called lyotropic series), the discovery of which goes back to Franz Hofmeister in 1887 [32] . Cations and anions are ranked in two separate series according to their interaction with a solvent, specifically water [33–39] . The ability which ranks the ions in the Hofmeister series is called chaotropy.…”

“…AIE‐active ILCs were also obtained by combining pyridinium salts with wedge‐shaped appendages (Scheme 7, 12(X′′) ) [139] . Dong developed pyrrolo[3,2‐b]pyrrole ILCs with two pyridinium units at the peripheral rings, which were not AIE‐active but showed a stepwise increase of the photoluminescence intensity at the phase transition SmA to Cr upon cooling from the isotropic liquid (Scheme 7, 13 ) [35] …”

“… Diphenylacrylonitrile imidazolium salts 11(X′) reported by Yang, [138] pyridinium salts 12(X′′) described by Lai [139] and pyrrolo[3,2‐b]pyrrole salts 13 reported by Dong [35] …”

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.…”