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Second-harmonic generation (SHG) is a common technique with many applications. Common inorganic single-crystalline materials used to produce SHG light are effective using short IR/visible wavelengths but generally do not perform well at longer, technologically relevant IR wavelengths such as 1300, 1550, and 2000 nm. Efficient SHG materials possess many of the same key material properties as terahertz (THz) generators, and certain single-crystalline organic THz generation materials have been reported to perform at longer IR wavelengths. Consequently, this work focuses on characterizing three efficient organic THz generators for SHG, namely, DAST (trans-4-[4-(dimethylamino)-N-methylstilbazolium] p-tosylate), DSTMS (4-N,N-dimethylamino-4’-N’-methylstilbazolium 2,4,6-trimethylbenzenesulfonate), and the recently discovered generator PNPA ((E)-4-((4-nitrobenzylidene)amino)-N-phenylaniline). All three of these crystals outperform the beta-barium borate (BBO), an inorganic material commonly used for SHG, using IR pump wavelengths (1200–2000 nm). 

Abstract The amination of aryl halides with palladium catalysts (Buchwald‐Hartwig amination) is a widely used transformation in synthetic and drug discovery chemistry. In this report, we demonstrate that a monometallic 2‐phosphinoimidazole Pd catalyst exhibits comparable or enhanced reactivity when compared to all ligands screened for room temperature amination of aryl chlorides with secondary amines. The di‐tert‐butylphosphine derivative showed extremely high reactivity while the di‐isopropyl variant led to almost complete loss of catalytic activity. Computational and experimental mechanistic and kinetic studies indicate that a monometallic Pd structure rather than a bimetallic Pd structure is key to fast catalysis. The di‐tert‐butylphosphine ligand has fast catalysis because it thermodynamically disfavors the formation of a much less active bimetallic Pd complex. A wide substrate scope is demonstrated for the arylation of secondary amines with aryl chlorides using our new catalyst system. 

Organic nonlinear optical (NLO) crystals are among the most efficient (>1%) terahertz (THz) radiation generators. However, one of the limitations of using organic NLO crystals is that the unique THz absorptions in each crystal make it difficult to obtain a strong, smooth, and broad emission spectrum. In this work, we combine THz pulses from two complementary crystals, DAST and PNPA, to effectively fill in spectral gaps, creating a smooth spectrum with frequencies out to 5 THz. The combination of pulses also increases the peak-to-peak field strength from 1 MV/cm to 1.9 MV/cm. 

Abstract We report that treatment of several 2‐diphenylphosphinoimidazoles with Pd(II) salts generates monosubstituted N−H NHC−Pd complexes via insertion into the C−P bond. Removal of the N−H proton in situ leads to anionic (X‐type) or imidazolyl‐Pd complexes that are highly stable and catalytically active, achieving up to 340,000 turnovers at 1 ppm catalyst loading in Suzuki‐Miyaura reactions. DFT‐calculated Tolman electronic parameters for the sterically small ligands suggest that these ligands are significantly more donating than traditional NHCs, which provides a rationale for rapid cross‐coupling catalysis. Excellent reactivity is also demonstrated in Sonogashira reactions. magnified image