Full-Color Tunable Photoluminescent Ionic Liquid Crystals Based on Tripodal Pyridinium, Pyrimidinium, and Quinolinium Salts

Abstract

Color-tunable luminescent ionic liquid crystals have been designed as a new series of luminescent materials. To achieve tuning of emission colors, intramolecular charge transfer (ICT) character has been incorporated into tripodal molecules. A series of the compounds has three chromophores in each molecule, incorporated with both electron-donating moieties such as alkylaminobenzene and alkoxybenzene, and electron-accepting moieties such as pyridinium, pyrimidinium, and quinolinium parts. These C(3)-symmetrical molecules self-assemble into liquid-crystalline (LC) columnar (Col) structures over wide temperature ranges through nanosegregation between ionic moieties and nonionic aliphatic chains. Photoluminescent (PL) emissions of these tripodal molecules are observed in the visible region both in the self-assembled condensed states and in solutions. For example, a pyrimidinium salt with didodecylaminobenzene moieties exhibits yellowish orange emission (λ(em) = 586 nm in a thin film). Multicolor PL emissions are successfully achieved by simple tuning of changing electron-donating and electron-accepting moieties of the compounds, covering the visible region from blue-green to red. It has been revealed that ICT processes in the excited states and weak intermolecular interactions play important roles in the determination of the PL properties of the materials, by measurements of UV-vis absorption and emission spectra, fluorescence lifetimes, and PL quantum yields.

Electrofluorochromism in π-conjugated ionic liquid crystals

“…It is worth highlighting that compounds 1 and 2 exhibit high fluorescent quantum yields (F) either in the liquid crystalline phases or in the solid state at room temperature (Table 1), among the highest ever reported [19][20][21][22] .…”

“…However, the synthesis of fluorescent liquid crystal including ionic ones, is challenging because of aggregation-caused fluorescent quenching [19][20][21][22] . Thus, electrofluorochromic liquid crystals have not been reported yet.…”

Effect of counterion on the mesomorphic behavior and optical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine

“…Recent reports showed that this type of pyridinium-based ionic liquid crystals [14,15] could be good candidates for emission-based applications. For this reason, the optical properties of pyridinium salts have been investigated and the results are summarized in Table 2.…”

Ionic Liquid Crystals Based on Pyridinium Salts

“…Photoluminescent tripodal pyridinium-based ionic liquid crystals were reported by Kato et al [64,65]. These tricationic pyridinium salts show thermotropic hexagonal or rectangular columnar phases or cubic phases with a large temperature ranges.…”