Rational Perturbation of the Fluorescence Quantum Yield in Emission‐Tunable and Predictable Fluorophores (Seoul‐Fluors) by a Facile Synthetic Method Involving C?H Activation

Fluorescence imaging enables the uniquely sensitive observation of functional‐ and molecular‐recognition events in living cells. However, only a limited range of biological processes have been subjected to imaging because of the lack of a design strategy and difficulties in the synthesis of biosensors. Herein, we report a facile synthesis of emission‐tunable and predictable Seoul‐Fluors, 9‐aryl‐1,2‐dihydrolopyrrolo[3,4‐b]indolizin‐3‐ones, with various R¹ and R² substituents by coinage‐metal‐catalyzed intramolecular 1,3‐dipolar cycloaddition and subsequent palladium‐mediated C H activation. We also showed that the quantum yields of Seoul‐Fluors are controlled by the electronic nature of the substituents, which influences the extent of photoinduced electron transfer. On the basis of this understanding, we demonstrated our design strategy by the development of a Seoul‐Fluor‐based chemosensor 20 for reactive oxygen species that was not accessible by a previous synthetic route.     

Doped Lead Halide White Phosphors for Very High Efficiency and Ultra-High Color Rendering

Near-UV-pumped white-light-emitting diodes with ultra-high color rendering and decreased blue-light emission is highly desirable. However, discovering a single-phase white light emitter with such characteristics remains challenging. Herein, we demonstrate that Mn doping as low as 0.027 % in the hybrid post-perovskite type (TDMP)PbBr₄ (TDMP=trans-2,5-dimethylpiperaziniium) enables to achieve a bright pure white emission replicating the spectrum of the sun's rays. Thus, a white phosphor exhibiting an emission with CIE coordinates (0.330, 0.365), a high photoluminescence quantum yield of 60 % (new record for white light emission of hybrid lead halides), and an ultra-high color rendering index (CRI=96, R9=91.8), corresponding to the record value for a single phase emitter was obtained. The investigation of the photoluminescence properties revealed how free excitons, self-trapped excitons, and low amount of Mn dopants are coupled to give rise to such pure white emission.     

Pre‐oxidation of Gold Nanoclusters Results in a 66 % Anodic Electrochemiluminescence Yield and Drives Mechanistic Insights

Gold nanoclusters (AuNCs) are attractive electrochemiluminescence (ECL) emitters because of their excellent stability, near IR emission, and biocompatibility. However, their ECL quantum yield is relatively low, and our limited fundamental understanding has hindered rational improvement of this parameter. Herein, we report drastic enhancement of the ECL of ligand‐stabilized AuNCs by on‐electrode pre‐oxidation with triethylamine (TEA) as a co‐reactant. The l ‐methionine‐stabilized AuNCs resulted in a record high ECL yield of 66 %. This strategy was successfully extended to other AuNCs, and it is more effective for ligand shells that allow more effective electron transfer. In addition, excitation of the pre‐oxidized ECL required a lower potential than conventional methods, and no additional instrument was required. This work opens avenues for solving a challenging problem of AuNC‐based ECL probes and enriches fundamental understanding, greatly broadening their potential applications.     

Simultaneous Long‐Persistent Blue Luminescence and High Quantum Yield within 2D Organic–Metal Halide Perovskite Micro/Nanosheets

Molecular solid‐state materials with long‐lived luminescence (such as thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) systems) are promising for display, sensoring, and bio‐imaging applications. However, the design of such materials that exhibit both long luminescent lifetime and high solid‐state emissive efficiency remains an open challenge. Two‐dimensional (2D) organic–metal halide perovskite materials have a high blue‐emitting quantum yield of up to 63.55 % and ultralong TADF lifetime of 103.12 ms at ambient temperature and atmosphere. Our design leverages the combined influences of a 2D space/electronic confinement effect and a modest heavy‐atom tuning strategy. Photophysical studies and calculations reveal that the enhanced quantum yield is due to the rigid laminate structure of perovskites, which can effectively inhibit the non‐radiative decay of excitons.     

Optomechanical Control of Quantum Yield in Trans–Cis Ultrafast Photoisomerization of a Retinal Chromophore Model

The quantum yield of a photochemical reaction is one of the most fundamental quantities in photochemistry, as it measures the efficiency of the transduction of light energy into chemical energy. Nature has evolved photoreceptors in which the reactivity of a chromophore is enhanced by its molecular environment to achieve high quantum yields. The retinal chromophore sterically constrained inside rhodopsin proteins represents an outstanding example of such a control. In a more general framework, mechanical forces acting on a molecular system can strongly modify its reactivity. Herein, we show that the exertion of tensile forces on a simplified retinal chromophore model provokes a substantial and regular increase in the trans ‐to‐cis photoisomerization quantum yield in a counterintuitive way, as these extension forces facilitate the formation of the more compressed cis photoisomer. A rationale for the mechanochemical effect on this photoisomerization mechanism is also proposed.