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Efficient and selective electrochemical hydrodehalogenation of organic halides remains a significant challenge in electrocatalysis due to competing side reactions, low Faradaic efficiency, and stringent solubility requirements. Herein, we introduce a design of Janus palladium membrane electrode (J-Pdm) that enables the direct generation and transfer of hydride species from water reduction in a dual-cell configuration. This design facilitates heterogeneous hydride transfer in an aprotic environment, achieving rapid reaction rate and superior Faradaic efficiency compared to conventional electrochemical hydrogenation systems and traditional electrochemical palladium membrane reactors. Notably, J-Pdm efficiently catalyzes the hydrodehalogenation of unactivated alkyl halides, a challenging transformation that suffers from poor efficiency in traditional electrocatalytic systems. Furthermore, J-Pdm enables the site-selective deuteration of pharmaceutical molecules, as demonstrated in the gram-scale synthesis of deuterated ibuprofen using D2O as the deuterium source. This work demonstrates J-Pdm as a powerful and versatile platform for electrocatalytic hydrogenation, hydrogenolysis, and isotopic labeling, offering a competent alternative to conventional electrochemical strategies and exhibiting broad industrial and pharmaceutical applications. 

Precision deuteration at metabolically vulnerable sites of pharmaceuticals can enhance drug stability and therapeutic efficacy, yet existing methods often suffer from poor selectivity and inefficiency. Here, we report an electricity-driven bromine-mediated deuteration strategy that enables late-stage site-selective deuteration of pharmaceuticals using D2O as the deuterium source. This approach involves a two-step process: (i) bromination of labile C–H bonds using Br2, followed by (ii) electricity-driven deuterodebromination using a palladium membrane reactor. This design leverages in situ Br2 generation at the anode and selective deuterium permeation through the palladium membrane cathode, thereby significantly improving atom economy and energy efficiency. Our method achieves nearly complete conversion and >90% deuterium incorporation for a range of aryl, heteroaryl, benzylic, and unactivated alkyl bromides, including ten marketed drug molecules. Furthermore, gram-scale synthesis of D-clonidine demonstrates the scalability of this approach. By integrating high selectivity, broad substrate scope, and operational efficiency, this method offers a practical solution for deuterated drug synthesis, with potential applications in pharmaceutical development and metabolic stabilization. 

Terahertz (THz) quantum cascade lasers (QCLs) are technologically important laser sources for the THz range but are complex to model. An efficient extended rate equation model is developed here by incorporating the resonant tunneling mechanism from the density matrix formalism, which permits to simulate THz QCLs with thick carrier injection barriers within the semi-classical formalism. A self-consistent solution is obtained by iteratively solving the Schrödinger–Poisson equation with this transport model. Carrier–light coupling is also included to simulate the current behavior arising from stimulated emission. As a quasi-ab initio model, intermediate parameters, such as pure dephasing time and optical linewidth, are dynamically calculated in the convergence process, and the only fitting parameters are the interface roughness correlation length and height. Good agreement has been achieved by comparing the simulation results of various designs with experiments, and other models such as density matrix Monte Carlo and non-equilibrium Green's function method that, unlike here, require important computational resources. The accuracy, compatibility, and computational efficiency of our model enable many application scenarios, such as design optimization and quantitative insights into THz QCLs. Finally, the source code of the model is also provided in the supplementary material of this article for readers to repeat the results presented here, investigate, and optimize new designs. 

Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful to study ultrafast processes in MIR and THz using the targeted wavelength-by-design properties of QCLs. Since the first demonstration in 2009, mode-locking of QCLs has undergone considerable development in the past decade, which includes revealing the underlying mechanism of pulse formation, the development of an ultrafast THz detection technique, and the invention of novel pulse compression technology, etc. Here, we review the history and recent progress of ultrafast pulse generation from QCLs in both the THz and MIR regimes. 

Abstract A terahertz (THz) frequency comb capable of high-resolution measurement will significantly advance THz technology application in spectroscopy, metrology and sensing. The recently developed cryogenic-cooled THz quantum cascade laser (QCL) comb has exhibited great potentials with high power and broadband spectrum. Here, we report a room temperature THz harmonic frequency comb in 2.2 to 3.3 THz based on difference-frequency generation from a mid-IR QCL. The THz comb is intracavity generated via down-converting a mid-IR comb with an integrated mid-IR single mode based on distributed-feedback grating without using external optical elements. The grating Bragg wavelength is largely detuned from the gain peak to suppress the grating dispersion and support the comb operation in the high gain spectral range. Multiheterodyne spectroscopy with multiple equally spaced lines by beating it with a reference Fabry-Pérot comb confirms the THz comb operation. This type of THz comb will find applications to room temperature chip-based THz spectroscopy.