An efficient homogeneous catalytic system for the visible-light-induced production of hydrogen from water utilizing cyclometalated iridium(III) and tris-2,2'-bipyridyl rhodium(III) complexes is described. Synthetic modification of the photosensitizer Ir(C--N) 2(N--N) (+) and water reduction catalyst Rh(N--N) 3 (3+) creates a family of catalysts with diverse photophysical and electrochemical properties. Parallel screening of the various catalyst combinations and photoreaction conditions allows the rapid development of an optimized photocatalytic system that achieves over 5000 turnovers with quantum yields ( (1)/ 2 H 2 per photon absorbed) greater than 34%. Photophysical and electrochemical characterization of the optimized system reveals that the reductive quenching pathway provides the necessary driving force for the formation of [Rh(N--N) 2] (0), the active catalytic species for the reduction of water to produce hydrogen. Tests for system poisoning with mercury or CS 2 provide strong evidence that the system is a true homogeneous system for photocatalytic hydrogen production.

A photocatalytic water-reducing system utilizing a bis-cyclometalated bipyridyl iridium(III) photosensitizer (PS) and a platinum or palladium heterogeneous catalyst was used to identify systematic property-activity correlations among a library of structural derivatives of [Ir(ppy)(2)(bpy)](+). A heterogeneous Pd catalyst proved to be more durable than its previously reported Pt-based counterpart, allowing for more reliable photosensitizer study. The deliberate steric and electronic variations of the ppy and bpy moieties resulted in a dramatic decrease of the degradation rates observed with selected photosensitizers when compared to the more substitution-labile [Ir(ppy)(2)(bpy)](+) parent compound. An improved photosensitizer structure with a Pd catalyst in a nonligating solvent exhibited a 150-fold increase in catalyst turnover numbers compared to the system using [Ir(ppy)(2)(bpy)](+) and a Pt catalyst. Furthermore, photocatalytic and photophysical studies at varied temperatures provided information on the rate-limiting step of the photocatalytic process, which is shown to be dependent on both the PS and the Pt or Pd catalytic species.

The sun is a plentiful source of clean, renewable power, and the direct conversion of solar to chemical energy is a desirable goal. The collective efforts of the Bernhard group to develop molecular catalytic systems for visible-light water splitting are reviewed. Combinatorial synthesis and high-throughput screening techniques enabled the development of a series of photosensitizers with a wide range of photophysical and electrochemical properties. Parallel evaluation of the iridium(III) photosensitizers in photocatalytic water reduction systems utilizing cobalt-, platinum-, or rhodium-based water reduction catalysts resulted in systems that exhibited more than 5000 turnovers with quantum yields of 34% and turnover frequencies of 500 hr?1. For the complementary water oxidation system, the catalysts based on cyclometallated iridium complexes are robust and tunable, which allows for the rapid study of water oxidation reactions through targeted ligand modification.

Anti‐reflection (AR) coatings designed for glass and other rigid, inorganic substrates are commercially available; however, these inorganic AR coatings tend to crack or delaminate on flexible substrates. A polymeric film with a gradient refractive index (GRIN) profile would make an ideal AR coating for flexible substrates, but such coatings are challenging to fabricate using traditional, solution‐based techniques. Emulsion‐based resonant infrared, matrix‐assisted pulsed laser evaporation (RIR‐MAPLE) offers a straightforward approach to enabling the desired GRIN profile in polymeric materials. Two homopolymers (polystyrene (PS) and poly(methyl methacrylate) (PMMA)) are deposited as a blend and one component (PMMA) is dissolved, leaving behind a porous PS film. The porosity and refractive index (RI) are controlled by the volume ratio of the two homopolymers in the film. Structural and optical characterizations, as well as comparison to modeled optical properties, confirm that porous films fabricated from polymer blends deposited by RIR‐MAPLE behave as effective media over most of the visible spectrum. While evidence for the partial collapse of the porous polymer networks is observed, the RI of the porous films is reduced from that of the bulk material. Importantly, these studies demonstrate that RIR‐MAPLE should enable broadband, omnidirectional, polymeric AR coatings appropriate for flexible substrates.

Graded index polymer films enable novel optics using rigid or flexible substrates, such as waveguides or anti-reflection coatings. Previously, such films have been fabricated by nanoimprint lithography or the decomposition of a single component in polymer blends. Yet, it is desirable to have precise control over the polymer film composition in order to have the most flexibility in designing refractive index profiles. Resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) is a polymer thin film deposition technique that enables multi-layer structures on a wide variety of substrate materials, regardless of the solubilities of constituent polymers. In this work, the feasibility of tuning the refractive index of blended polymer films of polystyrene and poly(methyl methacrylate) deposited by RIR-MAPLE is demonstrated. Different polymer blend film compositions are deposited using RIR-MAPLE by varying the polymer target ratio. Transmission electron microscopy and atomic force microscopy are used to characterize the film morphology.