Synthesis and Characterization of Photoluminescence Liquid Crystals Based on Flexible Chain-Bearing Pentafluorinated Bistolanes

Shigeyuki Yamada,Tsutomu Konno,Masaya Sato

doi:10.3390/cryst10070603

Abstract

The liquid-crystalline (LC) and photophysical properties of molecules are very sensitive to their electronic and molecular aggregate structures. Herein, to shed light on the structure–property relationships of pentafluorinated bistolane-based photoluminescence (PL) liquid crystals (PLLCs) previously reported by our group, we synthesized pentafluorinated bistolanes with variable flexible chains and evaluated their LC and photophysical properties. The incorporation of an oxygen atom (to afford a 2-methoxyethoxy unit) or an oxygen atom and a methyl group (to afford a 1-methoxyprop-2-oxy unit) into the flexible butoxy chain significantly decreased the temperature of the crystalline-to-LC phase transition, and a chiral nematic phase comprising helical molecular aggregates was observed for the chiral 1-methoxyprop-2-oxy group–bearing bistolane. The synthesized bistolanes exhibited strong blue PL in both solution and crystalline phases; the featuring PL characteristics were maintained in the LC phase (produced by the crystalline-to-LC phase transition) except for a slight PL color change. Thus, it was concluded that the PL behavior of pentafluorinated bistolanes can be modulated by the choice of a suitable flexible chain, and the obtained insights are believed to facilitate the application of PLLCs in thermosensing PL materials.

Highlights

The development of novel light-emitting (LE) materials has attracted much attention, as they are widely used to detect cancer cells and protein localization/activity [1,2,3,4,5] and can find optoelectronic applications, e.g., in lighting or displays [6,7,8,9,10]
It was concluded that the PL behavior of pentafluorinated bistolanes can be modulated by the choice of a suitable flexible chain, and the obtained insights are believed to facilitate the application of PLLCs in thermosensing PL materials
A fingerprint optical texture was observed in the mesophase, which clearly indicated the formation of a chiral nematic phase with helical molecular aggregates

Summary

Introduction

The development of novel light-emitting (LE) materials has attracted much attention, as they are widely used to detect cancer cells and protein localization/activity [1,2,3,4,5] and can find optoelectronic applications, e.g., in lighting or displays [6,7,8,9,10]. Various kinds of LE molecules featuring extended π-conjugated structures have been reported far [11], most of them display luminescence only in the solution phase because of aggregation-caused luminescence quenching in the solid phase [12]. Tang and co-workers [13,14,15,16] advocated several light emission phenomena, e.g., crystallization- or aggregation-induced emission; the development of LE molecules intensely emitting even in molecular aggregated (e.g., crystalline and liquid-crystalline (LC)) states remains challenging.

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Results

Conclusion