Chiroptical‐Conjugated Polymer/Chiral Small Molecule Hybrid Thin Films for Circularly Polarized Light‐Detecting Heterojunction Devices

Herein, a simple and facile strategy is described to obtain chiroptically active semiconductor thin films by blending of poly(3‐alkylthiophene)s, which are conventional achiral polymer semiconductors, and 1,1′‐binaphthyl (BN), a versatile chiral molecule. As expected, the intermolecular interaction between the two materials is important to extend the chirality of the binaphthyl molecules to the hybrid films. The controlled phase separation and crystallization of poly[3‐(6‐carboxyhexyl)thiophene‐2,5‐diyl] (P3CT) and binaphthyl hybrid films result in unique heterojunction bilayer thin‐film structures that consisted of BN microcrystals at the top and a P3CT/BN mixed layer at the bottom. Such heterojunction bilayer films exhibit significantly amplified chiroptical response with weak broadened tails, which is due to the enhanced crystallization of the chiral BN molecules and formation of heteroaggregates in the hybrid films. Based on the characterization of crystalline structure and photoluminescence analysis, it is found that new electronic energy states are formed in the conduction band region of P3CTs in the P3CT/BN heteroaggregates, which contribute to chirality transfer from BN to the hybrid films. As a proof of concept, a photodiode capable of distinguishably sensing the left‐ and right‐handed circularly polarized light is successfully fabricated by using the hybrid films with the heterojunction bilayer structure.     

Sub-picosecond spin relaxation of bright excitons and imbalance suppression in asymmetric Cdse/Zns nanocrystal quantum dots under an applied magnetic field

The ultrafast spin dynamics of the bright exciton in CdSe/ZnS nanocrystal quantum dots has been investigated using a circularly polarized pump-probe experiment. A remarkably fast spin flip (-500 fs) of the bright exciton was observed at 4 K, which is attributed to the anisotropic electron-hole exchange interaction and the random positioning of nanocrystal quantum dots. In the presence of an applied magnetic field (5 T), the exciton spin parallel to the external magnetic field was favored due to Zeeman splitting. We found that this imbalance can possibly be suppressed by the state-blocking and the mixing of the 1(L) and 1(U) states in asymmetric quantum dots.     

High‐Speed Colloidal Quantum Dot Photodiodes via Accelerating Charge Separation at Metal–Oxide Interface

With ever‐growing technological demands in the imaging sensor industry for autonomous driving and augmented reality, developing sensors that can satisfy not only image resolution but also the response speed becomes more challenging. Herein, the focus is on developing a high‐speed photosensor capable of obtaining high‐resolution, high‐speed imaging with colloidal quantum dots (QDs) as the photosensitive material. In detail, high‐speed QD photodiodes are demonstrated with rising and falling times of τ_r = 28.8 ± 8.34 ns and τ_f = 40 ± 9.81 ns, respectively, realized by fast separation of electron–hole pairs due to the action of internal electric field at the QD interface, mainly by the interaction between metal oxide and the QD's ligands. Such energy transfer relations are analyzed and interpreted with time‐resolved photoluminescence measurements, providing physical understanding of the device and working principles.     

Conjugated Polyelectrolyte and Aptamer Based Potassium Assay via Single‐ and Two‐Step Fluorescence Energy Transfer with a Tunable Dynamic Detection Range

A new potassium ion detection assay was developed using a dye‐labeled aptamer and conjugated polyelectrolyte (CPE) as a signaling platform via 1‐step and 2‐step fluorescence resonance energy transfer. Guanine‐rich K⁺‐specific aptamers were designed as K⁺ ion recognition species with 6‐carboxyfluorescein (6‐FAM) and 6‐carboxytetramethylrhodamine (6‐TAMRA) at both termini. In the presence of K⁺ ions, the aptamers undergo a conformational change from an unfolded to folded form by forming a G‐quadruplex with K⁺, bringing two dyes in proximity. FRET‐induced 6‐TAMRA emission was proportional to [K⁺] in a range of 22.5 μm –100 mm in water without interference by the presence of excess Na⁺ ions (100 mm ). Upon the addition of CPE, a two‐step FRET process from CPE to 6‐TAMRA via 6‐FAM was enabled, showing an intensified 6‐TAMRA signal with K⁺ ions. The dynamic detection range and limit of detection (LOD) was fine‐tuned from ～millimolar to ～nanomolar concentrations of K⁺ by modulating the signal amplification effect of CPE. The LOD was determined to be ≈3.0 nm . This detection assay also showed high selectivity against other metal ions. This sensing scheme can be extended to the detection of a wide range of target materials by simply modifying the recognition aptamer sequence.