2-Chloroalkoxy-Substituted Pentafluorinated Bistolanes as Novel Light-Emitting Liquid Crystals

Abstract

In this study, we designed and synthesized novel pentafluorinated bistolane derivatives with 2-chloropentyl or 2-chlorohexyl flexible units as novel light-emitting liquid crystals (LELCs). By measuring the phase-transition behaviors, all derivatives were found to display liquid-crystalline (LC) phases during both heating and cooling processes. Among the novel bistolanes, the S- and R-configured derivatives exhibited a chiral nematic (N*) phase with a typical Grandjean optical texture. Interestingly, the chiral derivatives also exhibited a blue phase with a typical platelet texture in a narrow temperature range (2–4 °C). Photophysical measurements revealed that the 2-chloroalkoxy-substituted pentafluorinated bistolanes exhibited intense photoluminescence (PL) both in solution and in crystalline phases. The PL characteristics, especially the maximum PL wavelength, were found to switch sensitively during the heating and cooling cycles depending on the molecular aggregates through the crystal (Cr) ⇄ N* phase transition. The 2-chloroalkoxy flexible units induced dynamic changes in the LC and PL properties, providing valuable insight into the potential of various LELCs as PL sensing materials.

Development of fluorinated benzils and bisbenzils as room-temperature phosphorescent molecules

“…Over the past few years, our group has intensively investigated fluorinated 1,4-bis(2-phenylethyn-1-yl)benzenes (1), a structural class known as bistolanes (Figure 2A), which show prominent fluorescence not only in dilute solution, but also in the crystalline state [27][28][29][30][31].…”

Luminescence Tuning of Fluorinated Bistolanes via Electronic or Aggregated-Structure Control

“…1 H and 13 C NMR spectra were recorded using a Bruker AVANCE III 400 NMR spectrometer ( 1 H: 400 MHz and 13 C: 100 MHz, Bruker Corporation, Rheinstetten, Germany) in chloroform-d (CDCl3) solution, and the chemical shifts are reported in parts per million (ppm) using the residual proton in the NMR solvent (δH = 7.26 ppm for CHCl3 and δC = 77 ppm for CDCl3). 19 F NMR (376 MHz) spectra were recorded using a Bruker AVANCE III 400 NMR spectrometer in CDCl3 solution with CFCl3 (δF = 0 ppm) as an internal standard. Infrared (IR) spectra were acquired via the KBr method using a JASCO FT/IR-4100 type A spectrometer (JASCO Corporation, Tokyo, Japan); all spectra are reported in wavenumbers (cm −1 ).…”

“…Over the past few decades, numerous fluorine-containing organic materials have been developed because chemical reactivity and material properties are dramatically influenced by the unique characteristics of fluorine, e.g., the largest electronegativity of all elements, the second smallest atom has extensively studied efficient synthetic protocols for organofluorine molecules containing CF3 groups [14,15] and CF2CF2 fragments [16,17]. More recently, we have also developed a significant interest in functional materials, e.g., liquid-crystalline (LC) and photoluminescence (PL) materials, based on fluorinated π-conjugated molecules such as pentafluorophenyl-containing tolane [18] and bistolane molecules [19][20][21][22][23]. Intriguingly, bistolanes 1aA and 1bA (Figure 1a) exhibited blue-light PL in solution as well as in crystalline (Cr) phases [23].…”

Fluorinated Tolane Dyads with Alkylene Linkage: Synthesis and Evaluation of Photophysical Characteristics

“…In spite of their wide utility, progress in terms of the molecular design of solid-state photoluminescent molecules has been quite limited; accordingly, the search for efficient solid-state photoluminescent molecules is still on. Since a few years ago, we have extensively developed solid-state photoluminescent molecules based on the extended π-conjugated structure containing a fluorinated aromatic structure, which induces electron-density distribution owing to its large electronegativity and forms a tight crystal structure via van der Waals and hydrogen bonding interactions [22][23][24][25][26][27][28]. Among them, polyfluorinated tolane 1a [27] displayed highly efficient blue photoluminescence (PL) (ΦPL = 0.73) in crystalline states, although the PL efficiency was observed to be significantly low in dilute solution (ΦPL = ~0.04) (Figure 1a).…”