Circularly Polarized Luminescence Induced by Chiral Super Nanospaces

Abstract

A simple methodology is developed to realize chiroptical function induced through superstructural chirality of a matrix of helical nanofilaments formed by achiral molecules. In this work, circularly polarized luminescence is demonstrated in nanosegregated mesophase comprising only achiral molecules. An achiral molecular mixture of a bent-core host and a rod-like guest blended with a fluorescent dye is prepared. Circularly polarized luminescence confirms that the chiral superstructure consisting only of achiral molecules may serve as a chiral super nanospace for inducing chiral emissions from the fluorescent dye that exhibits rod-like molecular ordering. In other words, the formation of a chiral superstructure by the segregated rod-like molecules embedded in helical nanofilaments (bent-core molecules) is confirmed. The results provide a novel strategy for constructing dissymmetric circularly polarized luminescence materials based on achiral molecules, which is potentially applicable in future information and display technologies.

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

“…This was consistent with the phase-transition temperatures of pure 8OCB, indicating that the nanoscale phase segregations occurred between P-7 and 8OCB. The evaluated glum values in <HNF/N> in the P-7 and 8OCB mixtures were 6 × 10 −3 -8 × 10 −3 , comparable to those in a similar <HNF/N> mixed system reported previously [11]. Meanwhile, the glum value in <HNF/SmA> was relatively larger than that in <HNF/N>.…”

“…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 2 of 6 attributed to the helix of the HNF affecting the structure of the embedded N phase doped with the guest dye, thereby forming self-assembled chiral aggregates associated with the helix of the HNF phase, despite having a mixed system consisting of only chemically achiral molecules.…”

“…This was Crystals 2020, 10, 952 2 of 6 attributed to the helix of the HNF affecting the structure of the embedded N phase doped with the guest dye, thereby forming self-assembled chiral aggregates associated with the helix of the HNF phase, despite having a mixed system consisting of only chemically achiral molecules. The calamitic guest dyes generally obey the orientational ordering of the rod-like mesogen while mixing with rod-like mesogenic molecules [11]. An N phase that is blended with the guest dye molecule and segregated from the HNFs forms chiral aggregates; therefore, circularly polarized luminescence, attributed to the dye molecules in the chiral aggregates, can be observed [11].…”

“…The calamitic guest dyes generally obey the orientational ordering of the rod-like mesogen while mixing with rod-like mesogenic molecules [11]. An N phase that is blended with the guest dye molecule and segregated from the HNFs forms chiral aggregates; therefore, circularly polarized luminescence, attributed to the dye molecules in the chiral aggregates, can be observed [11]. Because both the host and guest in the system are chemically achiral, this method can be regarded as an achiral host-achiral luminescent guest method.…”

Beyond Chiral Organic (p-Block) Chromophores for Circularly Polarized Luminescence: The Success of d-Block and f-Block Chiral Complexes

“…It is worth noting here that significant enhancement of g lum could be observed occasionally in nano-assemblies or in aggregated systems as a result of the formation of chiral microstructural materials or films (Geng et al, 2003 ; Kumar et al, 2015 ; Roose et al, 2016 ; Sang et al, 2019 ), in particular for few electroluminescent systems, such as OLEDs (Brandt et al, 2016 ; Song F. et al, 2018 ). In addition, the incorporation of emissive moieties into anisotropic media, such as chiral liquid crystals displaying helical macrostructures, proved to be an efficient strategy for the generation of strong CPL emission (Watanabe and Akagi, 2014 ; Goto, 2018 ; Gao et al, 2019 ; Kim et al, 2019 ; Li et al, 2019 ; Yang X. et al, 2019 ). Focusing on isotropic solutions, some recent up-converted CPL studies evidenced enhanced g lum compared to their downshifted counterparts.…”