Chiral self-assembly regulated photon upconversion based on triplet-triplet annihilation

Circular dichroism measurement of a single anisotropic chiral nanostructure using scanning circular dichroism microscopy

Circular dichroism (CD) spectroscopy is widely used to study the chiroptical properties of chiral materials, including films, solutions, and isotropic materials. However, measuring the CD signal of single anisotropic chiral nanostructures is challenging due to the presence of "artifact" signals, such as linear dichroism (LD) and linear birefringence (LB). In this study, we employed scanning circular dichroism microscopy (SCDM) to extract the intrinsic CD signal of the single DBD/LBL self-assembled chiral supramolecule. Using the Stokes-Mueller formalism, we analyzed the SCDM signal, which exhibited a sinusoidal dependence on the polarization angles of the laser beam. This approach enabled the determination of both the orientation and the intrinsic CD. The intrinsic CD of the single DBD self-assembled chiral supramolecule was 9.9 mdeg, while that of the single LBL self-assembled chiral supramolecule was -9.3 mdeg. SCDM provides a new method for measuring CD at the nanoscale, paving the way for future advancements in optoelectronic applications and introducing an approach for studying chiral nanomaterials.

Direct Crystallization Resolution of Racemates Enhanced by Chiral Nanorods: Experimental, Statistical, and Quantum Mechanics/Molecular Dynamics Simulation Studies

Three chiral nanorods of C14-l-Thea, C14-l-Phe, and C14-d-Phe were first synthesized and utilized as heterogeneous nucleants to enhance the resolution of racemic Asp via direct crystallization. Through the statistical analysis from 320 batches of nucleation experiments, we found that the apparent appearance diversity of two enantiomeric crystals of Asp existed in 80 homogeneous experiments without chiral nanorods. However, in 240 heterogeneous experiments with 4.0 wt % chiral nanorods of solute mass added, the appearance of those nuclei with the same chirality as the nanorods was apparently promoted, and that with the opposite chirality was totally inhibited. Under a supersaturation level of 1.08, the maximum ee of the initial nuclei was as high as 23.51%. When the cooling rate was 0.025 K/min, the ee of the product was up to 76.85% with a yield of 14.41%. Furthermore, the simulation results from quantum mechanics (QM) and molecular dynamics (MD) revealed that the higher chiral recognition ability of C14-l-Thea compared to C14-l-Phe that originated from the interaction difference between C14-l-Thea and Asp enantiomers was larger than that between C14-l-Phe and Asp enantiomers. Moreover, the constructed nanorods exhibited good stability and recyclability.

Highly Ordered 2D-Assemblies of Phase-Segregated Block Molecules for Upconverted Linearly Polarized Emission

Materials based on the laminar ordering of self-assembled molecules have a unique potential for applications requiring efficient energy migration through densely packed chromophores. Here, employing molecular assemblies of coil-rod-coil block molecules for triplet-triplet annihilation upconversion (TTA-UC) based on triplet energy migration with linearly polarized emission is reported. By covalently attaching discrete-length oligodimethylsiloxane (oDMS) to 9,10-diphenylanthracene (DPA), highly ordered 2D crystalline DPA sheets separated by oDMS layers are obtained. Transparent films of this material doped with small amounts of triplet sensitizer Pt^II octaethylporphyrin show air-stable TTA-UC under non-coherent excitation. Upon annealing, an increase in TTA-UC up to two orders of magnitude is observed originating from both an improved molecular ordering of DPA and an increased dispersion of the sensitizer. The molecular alignment in millimeter-sized domains leads to upconverted linearly polarized emission without alignment layers. By using a novel technique, upconversion imaging microscopy, the TTA-UC intensity is spatially resolved on a micrometer scale to visually demonstrate the importance of molecular dispersion of sensitizer molecules for efficient TTA-UC. The reported results are promising for anti-counterfeiting and 3D night-vision applications, but also exemplify the potential of discrete oligodimethylsiloxane functionalized chromophores for highly aligned and densely packed molecular materials.