Enhancement of Luminescence Dissymmetry Factor in Nano-Segregated Phase Generated by Phase Separation between Helical Nanofilaments and Liquid-Crystalline Smectic A Phase

Jae-Jin Lee,Suk-Won Choi

doi:10.3390/cryst10100952

Abstract

Although several methods exist for the synthesis of circularly polarized luminescent (CPL) materials, the methods are extremely complex and tedious. In recent years, the chiral host-achiral luminescent guest method and the achiral host-achiral luminescent guest method have been employed to fabricate CPL materials; however, the main disadvantage of the latter is the small luminescence dissymmetry factor (glum) that limits the practical applications of the method. Therefore, this study reports on the enhancement of glum in a nano-segregated phase system, generated by the phase separation between helical nanofilaments (HNFs; originating from an achiral bent-core molecule) and a liquid-crystalline (LC) smectic A (SmA) phase (originating from an achiral rod-like mesogen). The observed glum value in the nano-segregated phase between the HNFs and LC SmA phase was larger than that in the nano-segregated phase between the HNFs and LC nematic (N) phase. The enhancement of the glum value was attributed to the order parameter (S) of the dye molecules in the SmA phase being larger than that in the N phase. Therefore, we concluded that the S value of the fluorescent dye molecules, doped into the embedded LC phase between the HNFs, strongly influenced the glum value.

Highlights

The synthesis of circularly polarized luminescent (CPL) materials is extremely complicated [1].the process itself is long and arduous, and cannot ensure circularly polarized emissions from the synthesized materials
We observed an enhancement in the glum value in a nano-segregated phase system, generated by the phase separation between helical nanofilaments (HNFs) and a LC smectic A (SmA) phase
The S value of the dye molecule blended into the SmA phase was larger than that of the the N phase)

Summary

Introduction

The process itself is long and arduous, and cannot ensure circularly polarized emissions from the synthesized materials. In recent years, another method has been employed as a general and versatile approach for fabricating CPL materials, termed the chiral host-achiral luminescent guest method [1,2,3], wherein achiral luminescent guest molecules are embedded into chiral molecules that form chiral aggregates. A recent study reported on an intriguing method to fabricate CPL materials using the aforementioned nano-segregated phase. The latter was blended with a fluorescent molecule (guest dye), and the CPL material was successfully obtained [11]. This was Crystals 2020, 10, 952; doi:10.3390/cryst10100952 www.mdpi.com/journal/crystals

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Conclusion