Donor-π-Acceptor-Type Fluorinated Tolane Containing a Semifluoroalkoxy Chain as a Condensed-Phase Luminophore

Abstract

Photoluminescent liquid-crystalline (PLLC) molecules, which can easily tune the PL behavior through the crystal (Cry)–LC phase transition, have attracted significant attention. Previously, we have demonstrated that the incorporation of a semifluoroalkoxy chain into π-conjugated mesogen is a promising approach for developing PLLC molecules with PL and SmA LC characteristics. We focused on the LC and PL characteristics of the molecules induced by the semifluoroalkoxy chain and fluorinated tolanes in the condensed phase. In this study, we developed cyano- or ethoxycarbonyl-terminated donor-π-acceptor-type fluorinated tolanes containing a semifluoroalkoxy flexible chain. The cyano-terminated fluorinated tolanes exhibited intense light-blue photoluminescence in the crystalline phase and did not exhibit any LC phase. In contrast, blue photoluminescence in the ethoxycarbonyl-terminated analogs was slightly weak; however, they exhibited Cry–SmA phase transition during the heating and cooling processes. The PL intensity of the ethoxycarbonyl-terminated fluorinated tolanes significantly decreased in the SmA phase; however, their PL colors changed during the Cry–SmA phase transition. This indicates that the developed tolanes are promising temperature-dependent PL materials, such as PL thermosensors or PL thermometers.

Development of Donor‐π‐Acceptor‐Type Fluorinated Tolanes as Compact Condensed Phase Luminophores and Applications in Photoluminescent Liquid‐Crystalline Molecules

“…The fluorinated tolanecarboxylate 18-F with a semifluoroalkoxy-type flexible chain showed PL even in the N phase, whereas λ PL was blue-shifted approximately 20 nm to exhibit a light-blue PL (Figure 24a). [29] The fluorinated tolane dimer 19-F 10 connected by a decylene chain and 20-F 5 connected by a pentylene chain also caused a slight blue shift of λ PL through phase transition between Cry and N or SmA LC phases (Figures 24b and 24c). [32,33] Similar to 18-F, it was found that PL intensity of 19-F 10 and 20-F 5 caused a significant decrease in the molecular aggregates of LC phase.…”

“…[28] Thus, we investigated 17-F with a CN group and 18-F with an COOEt group (Figure 13). [29] We initially investigated the phase transition behavior 15-F and 16-F having a decyloxy chain, and 17-F and 18-F having a nonafluorodecyloxy chain. [29] Contrary to our expectations, unfortunately, both fluorinated tolanes with a decyloxy chain (15-F and 16-F) exhibited only phase-transitions between the crystalline (Cry) and the isotropic (Iso) phases during both the 2 nd heating and cooling processes (Figure 13b, Table 4).…”

(1E)-1,2-Diaryldiazene Derivatives Containing a Donor–π-Acceptor-Type Tolane Skeleton as Smectic Liquid–Crystalline Dyes

“…1 H nuclear magnetic resonance (NMR) (400 MHz) and 13 C NMR (100 MHz) spectra were acquired using an AVANCE III 400 NMR spectrometer (Bruker, Rheinstetten, Germany) in chloroform-d (CDCl 3 ) solution, and chemical shifts are reported in parts per million (ppm) based on the residual protons or carbon in the NMR solvent. 19 F NMR (376 MHz) spectra were acquired using an AVANCE III 400 NMR spectrometer (Bruker, Rheinstetten, Germany) in CDCl 3 solution with C 6 F 6 (δ F = −163 ppm) as an internal stan-dard. Infrared (IR) spectra were recorded using the KBr method on a FTIR-4100 type A spectrometer (JASCO, Tokyo, Japan).…”

“…Recently, our group explored molecules that have both LC and photoluminescence properties and successfully developed donor-π-acceptor (D-π-A)-type tolane derivatives that have an electron-donating alkoxy group and an electron-withdrawing cyano group at their molecular ends [17][18][19]. Among our achievements, the D-π-A-type tolane bearing a decyloxy (C10H21O) chain formed a nematic (N) LC phase as a mesophase (Figure 1a) [19].…”

“…Recently, our group explored molecules that have both LC and photoluminescence properties and successfully developed donor-π-acceptor (D-π-A)-type tolane derivatives that have an electron-donating alkoxy group and an electron-withdrawing cyano group at their molecular ends [17][18][19]. Among our achievements, the D-π-A-type tolane bearing a decyloxy (C10H21O) chain formed a nematic (N) LC phase as a mesophase (Figure 1a) [19]. However, the formation of a mesophase of smectic A (SmA) was observed when the flexible chain was changed from a decyloxy chain to a semifluoroalkoxy chain, viz., C4F9-C6H12O or C6F13-C4H8O, in which a fluoroalkyl unit was introduced into the flexible-chain end (Figure 1b) [20].…”