Lead halide perovskites (LHPs) have shown remarkable promise for use in photovoltaics, photodetectors, light-emitting diodes, and lasers. Although solution-processed polycrystalline films are the most widely studied morphology, LHP nanowires (NWs) grown by vapor-phase processes offer the potential for precise control over crystallinity, phase, composition, and morphology. Here, we report the first demonstration of self-catalyzed vapor-liquid-solid (VLS) growth of lead halide (PbX; X = Cl, Br, or I) NWs and conversion to LHP. We present a kinetic model of the PbX NW growth process in which a liquid Pb catalyst is supersaturated with halogen X through vapor-phase incorporation of both Pb and X, inducing growth of a NW. For PbI, we show that the NWs are single-crystalline, oriented in the ⟨1̅21̅0⟩ direction, and composed of a stoichiometric PbI shaft with a spherical Pb tip. Low-temperature vapor-phase intercalation of methylammonium iodide converts the NWs to methylammonium lead iodide (MAPbI) perovskite while maintaining the NW morphology. Single-NW experiments comparing measured extinction spectra with optical simulations show that the NWs exhibit a strong optical antenna effect, leading to substantially enhanced scattering efficiencies and to absorption efficiencies that can be more than twice that of thin films of the same thickness. Further development of the self-catalyzed VLS mechanism for lead halide and perovskite NWs should enable the rational design of nanostructures for various optoelectronic technologies, including potentially unique applications such as hot-carrier solar cells.

Electronic spin-state dynamics were studied for a series of Au25(SC8H9)18q and Au24Pd(SC8H9)18 monolayer-protected clusters (MPCs) prepared in a series of oxidation states, q, including q = −1, 0, +1. These clusters were chosen for study because Au25(SC8H9)18−1 is a closed-shell superatomic cluster, but Au25(SC8H9)180 is an open-shell (7-electron) system; Au25(SC8H9)18+1 and PdAu24(SC8H9)180 are isoelectronic (6-electron) closed-shell systems. Carrier dynamics for electronic fine structure spin states were isolated using femtosecond time-resolved circularly polarized transient-absorption spectroscopy (fs-CPTA). Excitation energies of 1.82 eV and 1.97 eV were chosen for these measurements on Au25(SC8H9)180 in order to achieve resonance matching with electronic fine structure transitions within the superatomic P- and D-orbital manifolds; 1.82-eV excited an unpaired Pz electron to D states, whereas 1.97-eV was resonant with transitions between filled Px and Py subshells and higher-energy D orbitals. fs-CPTA measurements revealed multiple spin-polarized transient signals for neutral (open shell) Au25(SC8H9)18, following 1.82-eV excitation, which persisted for several picoseconds; time constants of 5.03 ± 0.38 ps and 2.36 ± 0.59 ps were measured using 2.43 and 2.14 eV probes, respectively. Polarization-dependent fs-CPTA measurements of PdAu24(SC8H9)18 clusters exhibit no spin-conversion dynamics, similar to the isoelectronic Au25(SC8H9)18+1 counterpart. These observations of cluster-specific dynamics resulted from spin-polarized superatom P to D excitation, via an unpaired Pz electron of the open-shell seven-electron Au25(SC8H9)18 MPC. These results suggest that MPCs may serve as structurally well-defined prototypes for understanding spin and quantum state dynamics in nanoscale metal systems.

Solvent-dependentexcited-state relaxation dynamics of iron (III) tetra-4-Nmethylpyridylporphine (FeTMPyP) were investigated using steady-state and femtosecond spectroscopies. Soret absorption for water-dispersed FeTMPyP consisted of two spectrally broad components centered at 3.12 eV and 2.92 eV, corresponding to π → π* and charge-transfer (CT)transitions. The CT transition exhibited inverse-dielectric-dependent energy shifts. Following 400-nm excitation, dynamics proceeded by femtosecond internal conversion from the initially prepared π* state to the CT state, followed by solvent-dependent CT relaxation. The CT energy shifts and relaxation rates exhibited correlated dielectric dependences. CT absorption energy and relaxation dynamics of FeTMPyP are sensitive indicators of surrounding dielectric environments.

The adsorption orientation of the iron(III) tetrakis(1-methyl-4-pyridyl)porphine (FeTMPyP) μ-oxo-bridged dimer species located in the inter-particle gap of solid gold nanosphere (SGN) and hollow gold nanosphere (HGN) networks was studied using a combination of linear extinction and surface-enhanced Raman Scattering (SERS) measurements. Nanoparticle aggregation was accomplished by μM additions of iron porphyrin to the colloidal SGN and HGN solutions. Aggregation was monitored by measuring the UV-Visible-NIR extinction spectra of the nanoparticle systems; a broadened and red-shifted localized surface plasmon resonance (LSPR), relative to the LSPR of the isolated nanoparticles, indicated aggregate formation. In conjunction with the LSPR extinction measurements, wavelength-dependent SERS measurements were used to determine the orientation of the FeTMPyP with respect to the SGN and HGN surfaces.

In fabricating an artificial photosynthesis (AP) electrode for water oxidation, we have devised a semiconductor‐mediator‐catalyst structure that mimics photosystem II (PSII). It is based on a surface layer of vertically grown nanorods of Fe2O3 on fluorine doped tin oxide (FTO) electrodes with a carbazole mediator base and a Ru(II) carbene complex on a nanolayer of TiO2 as a water oxidation co‐catalyst. The resulting hybrid assembly, FTO|Fe2O3|−carbazole|TiO2|−Ru(carbene), demonstrates an enhanced photoelectrochemical (PEC) water oxidation performance compared to an electrode without the added carbaozle base with an increase in photocurrent density of 2.2‐fold at 0.95 V vs. NHE and a negatively shifted onset potential of 500 mV. The enhanced PEC performance is attributable to carbazole mediator accelerated interfacial hole transfer from Fe2O3 to the Ru(II) carbene co‐catalyst, with an improved effective surface area for the water oxidation reaction and reduced charge transfer resistance.