Phototuning Energy Transfer in Self‐Organized Luminescent Helical Superstructures for Photonic Applications

Abstract

Stimuli‐triggered changes in the emission color of functional materials are in demand for a variety of potential applications. Herein, a strategy to reversibly phototune fluorescence color in cholesteric liquid crystal (CLC) with self‐organized luminescent helical superstructure via fluorescence resonance energy transfer (FRET) is developed. This dynamic FRET system is constructed by doping with 1,2‐dithienyldicyanoethene‐based chiral fluorescent photoswitch (switch 7) as an acceptor and a conventional coumarin dye C6 as a donor into a nematic liquid crystal (LC) host. The efficient energy transfer from C6 to switch 7 in the LC media, which is evidenced by both of emission color shift and enhanced circularly polarized luminescence, can be modulated on the basis of reversible trans–cis photoisomerization of switch 7 upon visible/UV light irradiations, leading to the emission color change from orange to green. Noteworthily, the FRET efficiency can be significantly improved when CLCs are confined in the polymer microtubes. Preliminary demonstrations of the LC film and LC microtubes array for information display and encryption with ease of electrical operation between planar, homeotropic, and focal conic states or light manipulation are described.

Frontiers in circularly polarized luminescence: molecular design, self-assembly, nanomaterials, and applications

“…In the past several years, there have been more and more reports on chiral emissive liquid crystals (N*-LCs) as CPL-active materials. These materials can self-assemble as highly regular helical arrangement in LC medium after annealing treatment as a result of the LC-templated molecular reorientation, which is beneficial for the enlarged effect of the induced CPL signals [101][102][103][104][105][106][107]. In 2020, Cheng's group [101] realized the recyclable CPL response behavior in N*-LCs doped with the axially chiral molecules (R/S)-37 (Figure 12a).…”

Circularly polarized luminescent self‐organized helical superstructures: From materials and stimulus‐responsiveness to applications

“…Our group has reported several photosensitive CLCs based on chiral fluorescence photoswitches. [101][102][103][104][105][106][107] These photoswitches can undergo Z/E isomerization upon light irradiation, where the helical twisted power (HTP) value and fluorescence intensity vary between photostationary states (PSSs). For instance, by doping visible-light-driven chiral fluorescent molecular switch 4 into a nematic LC, a cholesteric phase was efficiently induced, which enabled strong CPL emission at 581 nm (Figure 10A).…”

Template Assisted Generation of Chiral Luminescence in Organic Fluorophores

“…The inversion in the sign of CPL and the tuning of CPL wavelength could be achieved (Zheng et al, 2018 ; He et al, 2019 ). Moreover, suitably designed fluorescence resonance energy transfer (FRET) and charge transfer systems have also been used to tailor the CPL emission using * NLC templates (Li et al, 2020 ; Lin et al, 2020 ). Thus, it is observed that doping achiral fluorescent dyes with * NLC is emerging as an effortless and efficient way of generating CPL active materials.…”