Two-coordinate carbene-M I -amide (cMa, M I = Cu, Ag, Au) complexes have emerged as highly efficient luminescent materials for use in a variety of photonic applications due to their extremely fast radiative rates through thermally activated delayed fluorescence (TADF) from an interligand charge transfer (ICT) process. A series of cMa derivatives was prepared to examine the variables that affect the radiative rate, with the goal of understanding the parameters that control the radiative TADF process in these materials. We find that blue-emissive complexes with high photoluminescence efficiencies (Φ PL > 0.95) and fast radiative rates (k r = 4 × 10 6 s −1 ) can be achieved by selectively extending the π-system of the carbene and amide ligands. Of note is the role played by the increased separation between the hole and electron in the ICT excited state. Analysis of temperature-dependent luminescence data and theoretical calculations indicate that the hole−electron separation exerts a primary effect on the energy gap between the lowest-energy singlet and triplet states (ΔE ST ) while keeping the radiative rate for the singlet state relatively unchanged. This interpretation provides guidelines for the design of new cMa derivatives with even faster radiative rates in addition to those with slower radiative rates and thus extended excited state lifetimes.Article pubs.acs.org/JACS

The ability of metal nanoparticles to concentrate light via the plasmon resonance represents a unique opportunity for funneling the solar energy in photovoltaic devices. The absorption enhancement in plasmonic solar cells is predicted to be particularly prominent when the size of metal features falls below 20 nm, causing the strong confinement of radiation modes. Unfortunately, the ultrashort lifetime of such near-field radiation makes harvesting the plasmon energy in small-diameter nanoparticles a challenging task. Here, we develop plasmonic solar cells that harness the near-field emission of 5 nm Au nanoparticles by transferring the plasmon energy to band gap transitions of PbS semiconductor nanocrystals. The interfaces of Au and PbS domains were designed to support a rapid energy transfer at rates that outpace the thermal dephasing of plasmon modes. We demonstrate that central to the device operation is the inorganic passivation of Au nanoparticles with a wide gap semiconductor, which reduces carrier scattering and simultaneously improves the stability of heat-prone plasmonic films. The contribution of the Au near-field emission toward the charge carrier generation was manifested through the observation of an enhanced short circuit current and improved power conversion efficiency of mixed (Au, PbS) solar cells, as measured relative to PbS-only devices.

Here, we report the effect of force applied to the biaryl backbone of a bisphosphine ligand on the rate of oxidative addition of bromobenzene to a ligand-coordinated palladium center. Local compressive and tensile forces on the order of 100 pN were generated using a stiff stilbene force probe. A compressive force increases the rate of oxidative addition, whereas a tensile force decreases the rate, relative to that of the parent complex of strain-free ligand. Rates vary by a factor of ∼6 across ∼340 pN of force applied to the complexes. The crystal structures and DFT calculations support that force-induced perturbation of the geometry of the reactant is negligible. The force-rate relationship observed is mainly attributed to the coupling of force to nuclear motion comprising the reaction coordinate. These observations inform the development of catalysts whose activity can be tuned by an external force that is adjusted within a catalytic cycle.

We have demonstrated the ability to control the mechanical properties of metallosupramolecular materials via choice of ligand binding group, as well as with external light irradiation. These photoresponsive Cr(III)-based materials were prepared from a series of modified hydrogenated poly(ethylene-co-butylene) polymers linked through metal-ligand interactions between a Cr(III) metal center and pyridyl ligand termini of the polymers. The introduction of these Cr(III)-pyridine bonds gave rise to new mechanical and optical properties of the polymer materials. Depending on the type of pyridyl ligand, density functional theory calculations revealed changes in coordination to the Cr(III), which ultimately led to materials with significantly different mechanical properties. Electronic excitation of the Cr(III) materials with 450 and 655 nm CW lasers (800 mW/cm(2)) resulted in generation of excited state photophysical processes which led to temporary softening of the materials up to 143 kPa (41.5%) in storage modulus (G') magnitude. The initial mechanical strength of the materials was recovered when the light stimulus was removed, and no change in mechanical properties was observed with light irradiation where there was no absorbance by the Cr(III) moiety. These materials demonstrate that introduction of metal-ligand bonding interactions into polymers enables the design and synthesis of photoresponsive materials with tunable optical-mechanical properties not seen in traditional polymeric materials.

Photochemical Nitric oxide releasing composite materials (Photo-NORMs) were prepared using biocompatible polymers and the photochemical nitric oxide donor complex (CrONO). We have demonstrated nitric oxide (NO) release from the solid composites for extended (>30 hours) and controlled (20-100 pmoles s(-1)) durations after visible light irradiation. Quantitation of the efficiency of NO release from the composites shows that polymer gas permeability most dramatically affects the overall efficiency (QY) of photochemical NO release, where polymers with higher gas permeability have a higher QY of nitric oxide release. Composites were also prepared with β-phase lanthanide-doped NaYF4 upconverting nanoparticles (UCNPs). Controlled Nitric oxide release was achieved via near infrared (NIR) irradiation. A prototype LED device shows proof-of-concept that such photoresponsive NO-releasing composites could be applied to implantable systems, where the amount of NO released is modulated by changing irradiation time and light intensity. This research provides the guidelines necessary to move towards device fabrication and testing in actual tissue to evaluate the photo-NORMS as a reliable option for nitric oxide release in vivo.