Color-Tunable Perovskite Nanomaterials with Intense Circularly Polarized Luminescence and Tailorable Compositions

The ability to design halide perovskite nanocrystals (PNCs) with circularly polarized luminescence (CPL) offers exceptional potential in photonic technologies. Despite recent inspiring advances, the creation of PNCs with full-color tailorablity, outstanding CPL, and long-term stability remains a substantial challenge. Herein, a robust strategy to craft CPL-active PNCs is reported, exhibiting appealing full-color tunable wavelengths, enhanced CPL, and prolonged stability. In contrast to conventional methodologies, this strategy utilizes chiral nematic mesoporous silica (CNMS) as host to render in situ confined growth of diverse achiral PNCs. By strategically engineering photonic bandgap, adjusting loading amount of PNCs, and manipulating cations/anion compositions of PNCs, robust CPL responses with tunable wavelength and intensity are successfully obtained. The resulting PNCs-CNMS achieves stable CPL emissions with full-color tunability and impressive luminescent dissymmetric factors up to -0.17. Remarkably, silica-based hosts as a protective barrier confer exceptional resistance to humidity, photodegradation, and thermal stability, even up to 95 °C. Furthermore, the ability to achieve reversible CPL switching within PNCs-CNMS is attainable by leveraging the responsiveness of CNMS matrix or dynamic behavior of impregnated PNCs. Additionally, circularly polarized light-emitting diode devices based on PNCs-CNMS can be conveniently fabricated. This research affords a powerful platform for designing functional chiroptical materials.

Circular Polarized Light Emission in Chiral Inorganic Nanomaterials

Chiral inorganic nanostructures strongly interact with photons changing their polarization state. The resulting circularly polarized light emission (CPLE) has cross-disciplinary importance for a variety of chemical/biological processes and is essential for development of chiral photonics. However, the polarization effects are often complex and their interpretation is dependent on the several structural parameters of the chiral nanostructure. CPLE in nanostructured media has multiple origins and several optical effects are typically convoluted into a single output. Analyzing CPLE data obtained for nanoclusters, nanoparticles, nanoassemblies, and nanocomposites from metals, chalcogenides, perovskite, and other nanostructures, it is shown here that there are several distinct groups of nanomaterials for which CPLE is dominated either by circularly polarized luminescence (CPL) or circularly polarized scattering (CPS); there are also many nanomaterials for which they are comparable. The following points are also demonstrated: 1) CPL and CPS contributions involve light-matter interactions at different structural levels; 2) contribution from CPS is especially strong for nanostructured microparticles, nanoassemblies, and composites; and 3) engineering of materials with strongly polarized light emission requires synergistic implementation of CPL and CPS effects. These findings are expected to guide development of CPLE materials in a variety of technological fields, including 3D displays, information storage, biosensors, optical spintronics, and biological probes.

Cellulose Nanocrystal Films with NIR-II Circularly Polarized Light for Cancer Detection Applications

Near-infrared circularly polarized light is attractive for wide-ranging applications. However, high-performance near-infrared circularly polarized light is challenging to realize. Here, we show that left-handed chiral photonic cellulose nanocrystal (CNC) films produced from ultrasonicated suspensions enable right-handed circularly polarized luminescence with a dissymmetry factor of -0.330 in the second near-infrared window (NIR-II). We present a theoretical analysis of the adverse effect of structural defects and luminescence intensity heterogeneity on the right-handed circularly polarized luminescence g_lum inside the bandgap and the occurrence of left-handed circularly polarized luminescence at the band edges. We demonstrate the potential of the chiral photonic CNC films with NIR-II circularly polarized light for cancer cell discrimination. The present work identifies key scientific questions in CNC-based circularly polarized luminescence materials research.

Dual-Mode Circularly Polarized Light Emission and Metal-Enhanced Fluorescence Realized by the Luminophore-Chiral Cellulose Nanocrystal Interfaces

Circularly polarized (CP) light has attracted wide attention for its great potential in broad applications. However, it remains a challenge to generate left-handed and right-handed circularly polarized (LCP and RCP) light from cellulose nanocrystal (CNC)-based materials only with an intrinsic left-handed chiral structure, owing to the pattern of CP light emission primarily based on the chirality of materials. Herein, a separation structure of luminophore layers and chiral CNCs was provided to achieve dual-mode CP light emission by building a luminophore-chiral CNC interface. By directly exciting the back and front of two-layer films, LCP and RCP light could be easily emitted without any assisting means and specific setting angles. In addition, owing to the formation of the luminophore-chiral CNC interface, metal-enhanced fluorescence (MEF) was achieved to offset the brightness loss caused by circular polarization. By incorporating gold triangular nanoprisms in CNC chiral layers, the fluorescence enhancement of the ensemble was as high as 6.5-fold. The decisive role of the luminophore-chiral CNC interface in enhancing luminescence and dual-mode CP light emission was carefully investigated by contrasting the systems with and without luminophore-chiral CNC interfaces in this study. We believe that this dual-mode CP light emission film with MEF enables a promising approach to extending the application of CP light materials.

Chiral Mesostructured BiOBr Films with Circularly Polarized Colour Response

Achieving strong and broadband circularly polarized colour responses in chiral inorganic materials is challenging. Here, we fabricated chiral mesostructured bismuth oxybromide (BiOBr) films (CMBFs) via hydrothermal growth using chiral sugar alcohols as symmetry-breaking agents. The layered slabs of BiOBr crystals with weak van-der-Waals interactions are prone to mismatching due to the chiral driving force, resulting in hierarchically chiral arrangements of fine size. Three levels of chirality exist in the CMBFs: primary, helical distortion crystal lattices of a nanoflake, secondary, helical stacking of nanoflakes to form nanoplates, and tertiary, chiral vortexes arranged by nanoplates. The CMBFs displayed optical activities (OAs) over a wide wavelength range of 350-2500 nm with an anisotropic factor of up to 0.99, which led to a significant chirality-dependent colour response to circularly polarized light. The high selectivity can be considered as the result of enhanced resonance due to structural-handedness matching and the synergistic effect of multiple OAs.

Template Assisted Generation of Chiral Luminescence in Organic Fluorophores

Development of efficient ways of fabricating chiral light emitting materials is an active area of research due to the vast potential offered by these materials in the field of optoelectronic devices, data storage, and asymmetric synthesis. Among the various methods employed, template assisted generation of chiral luminescence is gaining enormous attention due to its simplicity, applicability over a wide range of fluorescent molecules/dyes, and the display of high anisotropic values.

Silica covering driven intensity enhancement and handedness inversion of the CPL signals of the supramolecular assemblies

Dipeptide-based hybrid materials with enhanced and inversed circularly polarized luminescence signals were fabricated through a dynamic supramolecular templating approach.

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (g_abs and g_lum) and on the application of ECD and CPL to derive structural information on aggregated states.