Enabling High Precision Gradient Index Control in Subsurface Multiphoton Lithography.

Multiphoton lithography inside a mesoporous host can create optical components with continuously tunable refractive indices in three-dimensional (3D) space. However, the process is very sensitive at exposure doses near the photoresist threshold, leading previous work to reliably achieve only a fraction of the available refractive index range for a given material system. Here, we present a method for greatly enhancing the uniformity of the subsurface micro-optics, increasing the reliable index range from 0.12 (in prior work) to 0.37 and decreasing the standard deviation (SD) at threshold from 0.13 to 0.0021. Three modifications to the previous method enable higher uniformity in all three spatial dimensions: (1) calibrating the planar write field of mirror galvanometers using a spatially varying optical transmission function which corrects for large-scale optical aberrations; (2) periodically relocating the piezoelectrically driven stage, termed piezo-galvo dithering, to reduce small-scale errors in writing; and (3) enforcing a constant time between each lateral cross section to reduce variation across all writing depths. With this new method, accurate fabrication of optics of any index between n = 1.20 and 1.57 (SD < 0.012 across the full range) was achieved inside a volume of porous silica. We demonstrate the importance of this increased accuracy and precision by fabricating and characterizing calibrated two-dimensional (2D) line gratings and flat gradient index lenses with significantly better performance than the corresponding control devices. As a visual representation, the University of Illinois logo made with 2D line gratings shows significant improvement in its color uniformity across its width.

Super-compact universal quantum logic gates with inverse-designed elements.

Integrated quantum photonic circuit is a promising platform for the realization of quantum information processing in the future. To achieve the large-scale quantum photonic circuits, the applied quantum logic gates should be as small as possible for the high-density integration on chips. Here, we report the implementation of super-compact universal quantum logic gates on silicon chips by the method of inverse design. In particular, the fabricated controlled-NOT gate and Hadamard gate are both nearly a vacuum wavelength, being the smallest optical quantum gates reported up to now. We further design the quantum circuit by cascading these fundamental gates to perform arbitrary quantum processing, where the corresponding size is about several orders smaller than that of previous quantum photonic circuits. Our study paves the way for the realization of large-scale quantum photonic chips with integrated sources and can have important applications in the field of quantum information processes.

Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer Hydrogenation and Asymmetric Hydrogenation of Ketones.

Chiral alcohols are important building blocks in the pharmaceutical and fine chemical industries. The enantioselective reduction of prochiral ketones catalyzed by transition metal complexes, especially asymmetric transfer hydrogenation (ATH) and asymmetric hydrogenation (AH), is one of the most efficient and practical methods for producing chiral alcohols. In both academic laboratories and industrial operations, catalysts based on noble metals such as ruthenium, rhodium, and iridium dominated the asymmetric reduction of ketones. However, the limited availability, high price, and toxicity of these critical metals demand their replacement with abundant, nonprecious, and biocommon metals. In this respect, the reactions catalyzed by first-row transition metals, which are more abundant and benign, have attracted more and more attention. As one of the most abundant metals on earth, iron is inexpensive, environmentally benign, and of low toxicity, and as such it is a fascinating alternative to the precious metals for catalysis and sustainable chemical manufacturing. However, iron catalysts have been undeveloped compared to other transition metals. Compared with the examples of iron-catalyzed asymmetric reduction, cobalt- and nickel-catalyzed ATH and AH of ketones are even seldom reported. In early 2004, we reported the first ATH of ketones with catalysts generated in situ from iron cluster complex and chiral PNNP ligand. Since then, we have devoted ourselves to the development of ATH and AH of ketones with iron, cobalt, and nickel catalysts containing novel chiral aminophosphine ligands. In our study, the iron catalyst containing chiral aminophosphine ligands, which are expected to control the stereochemistry at the metal atom, restrict the number of possible diastereoisomers, and effectively transfer chiral information, are successful catalysts for enantioselective reduction of ketones. Among these novel chiral aminophosphine ligands, 22-membered macrocycle P2N4 exhibited extraordinary enantioselectivities when combined with iron(0) cluster Fe3(CO)12. A broad scope of ketones including aromatic, heteroaromatic, and ß-ketoesters can be reduced smoothly with excellent enantioselectivities (up to 99% ee) approaching or exceeding those achievable with the noble metal catalysts. Notably, the chiral iron-based catalyst proved to be highly efficient for both ATH as well as AH of various ketones. Until now, such "universal" catalyst is very rare. Preliminary studies suggest that the AH reaction most likely involved iron particles as the active catalytic species. These research results point to a new direction in developing viable effective nonprecious metal catalysts for asymmetric reduction and probably for other asymmetric catalytic reactions as well.

Iron catalyzed asymmetric hydrogenation of ketones.

Chiral molecules, such as alcohols, are vital for the manufacturing of fine chemicals, pharmaceuticals, agrochemicals, fragrances, and novel materials. These molecules need to be produced in high yield and high optical purity and preferentially catalytically. Among all the asymmetric catalytic reactions, asymmetric hydrogenation with H2 (AH) is the most widely used in the industry. With few exceptions, these AH processes use catalysts based on the three critical metals, rhodium, ruthenium, and iridium. Herein we describe a simple, industrially viable iron catalyst that allows for the AH of ketones, a process currently dominated by ruthenium and rhodium catalysts. By combining a chiral, 22-membered macrocyclic ligand with the cheap, readily available Fe3(CO)12, a wide variety of ketones have been hydrogenated under 50 bar H2 at 45-65 °C, affording highly valuable chiral alcohols with enantioselectivities approaching or surpassing those obtained with the noble metal catalysts. In contrast to AH by most noble metal catalysts, the iron-catalyzed hydrogenation appears to be heterogeneous.

Self-assembly of a Rh(I) complex on Au(111) surfaces and its electrocatalytic activity toward the hydrogen evolution reaction.

The self-assembly of a Wilkinson type of catalyst molecule, trans-RhCl(CO)(PPh3)2, on Au(111) surfaces and its electrocatalytic properties toward the hydrogen evolution reaction (HER) are investigated by employing scanning tunneling microscopy (STM), cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS). The self-assembled monolayers of RhCl(CO)(PPh3)2 are prepared from either dichloromethane or aqueous solutions, but the ordered structures are observed only in atmospheric conditions after solvents evaporate. In the electrolyte solutions, disordered yet uniformly sized spherical clusters of individual molecules are observed as a result of the conformational change of the molecule by the solvation effect of water. The immobilized Rh(I) molecular clusters are electrochemically stable in a wide potential window and exhibit remarkable electrocatalytic activity toward HER in perchloric acid solutions. Several comparative experiments involving similar types of immobilized complexes containing Ru(I) and Ir(I) centers and solution species of RhCl(CO)(PPh3)2 are performed. However, none of them are found to be electroactive to HER. The Tafel slope of HER on the Rh(I) complex modified Au(111) electrode in 0.1 M HClO4 is determined to be -0.061 V, which is almost in the middle of those on bare Au(111) (-0.093 V) and Rh covered (thetaRh approximately 0.3) Au(111) (-0.034 V) electrodes. XPS measurements reveal a valence change of Rh(I) to Rh(0), and an oxidative addition and reductive elimination mechanism is suggested for the enhancement of HER.

Kinetic resolution of racemic secondary alcohols catalyzed by chiral diaminodiphosphine-Ir(I) complexes.

Chiral diaminodiphosphine-Ir(I) complexes were found to efficiently catalyze enantioselective oxidation of racemic secondary alcohols in acetone. In the presence of base, oxidative kinetic resolution of the alcohols proceeded smoothly with excellent enantioselectivity (up to 98% ee) under mild conditions. [reaction: see text].

Highly efficient iridium catalyst for asymmetric transfer hydrogenation of aromatic ketones under base-free conditions.

[reaction: see text] Catalytic systems generated in situ from the chiral PNNP ligands with iridium or rhodium hydride complexes exhibited excellent catalytic activity and good enantioselectivity in the asymmetric transfer hydrogenation of aromatic ketones without added base. The best result was obtained in the IrH(CO)(PPh(3))(3)-ligand 2 catalytic system with up to 99% yield and 97% ee.

Highly efficient chiral metal cluster systems derived from Ru3(CO)12 and chiral diiminodiphosphines for the asymmetric transfer hydrogenation of ketones.

The chiral Ru cluster-based catalyst systems generated in situ from Ru3(CO)12 and chiral diiminodiphosphine tetradentate ligands effected asymmetric transfer hydrogenation of propiophenone in 2-propanol, leading to 1-phenyl-1-propanol in 94% yield and with 96% ee.