This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details.

Porphyrin aggregates have attractive photophysical properties for phototherapy and optical imaging, including quenched photosensitization, efficient photothermal conversion, and unique absorption spectra. Although hydrophobic porphyrin photosensitizers have long been encapsulated into liposomes for drug delivery, little is known about the membrane properties of liposomes with large amphiphilic porphyrin compositions. In this paper, a porphyrin-lipid conjugate was incorporated into liposomes formed of saturated or unsaturated lipids to study the membrane composition-dependent formation of highly ordered porphyrin J-aggregates and disordered aggregates. Porphyrin-lipid readily phase-separates in saturated membranes, forming J-aggregates that are destabilized during the ripple phase below the main thermal transition. Porphyrin-lipid J-aggregates are photostable with a photothermal efficiency of 54 ± 6%, comparable to gold. Even at high porphyrin-lipid compositions, porphyrin J-aggregates coexist with a minority population of disordered aggregates, which are photodynamically active despite being fluorescently quenched. For photothermal applications, liposome formulations that encourage porphyrin-lipid phase separation should be explored for maximum J-aggregation.

Excited-state properties of photonic materials play an important part in dictating the photocatalytic activity. Thiol-protected gold clusters, like Au(SR) and Au(SR), are an emerging material of interest with unique optical and electronic properties. Au(SR) clusters, in particular, have shown promise as one of the highest efficiency clusters in light harvesting, with a high emission quantum yield. In this work, the excited-state properties of Au(SR) are studied in-depth by ultrafast pump/probe spectroscopy for the first time. A single model describing the optical characteristics of thiol-protected Au(SR) and Au(SR) clusters is offered. Excited-state dynamics analysis suggests that there are state-resolved relaxations due to the presence of multiple excited states. The populations of these excited states are shown to be solvent- and ligand-dependent.

No abstract

Metal clusters are an emerging photonic material with a rapidly growing library of stable, atomically precise clusters recently reported. The growing interest in metal clusters, such as thiol-protected Au clusters, is due in part to interest in this new material for light harvesting, catalysis and electron transfer studies, and high efficiency photovoltaics (i.e., metal-cluster-sensitized solar cells (MCSSC) with long-term stability). Herein, we use cobalt redox couples as a tool to investigate the electronic properties (i.e., HOMO energy level) and the wavelength-dependent photocatalytic activities of glutathione protected gold clusters. To this purpose, we have synthesized a series of cobalt complexes with bipyridine and phenanthroline derivatives in order to study Au18(SR)14 and Au25(SR)18 sensitized solar cells. Using cobalt complex mediators as an alternative to the conventional high performance I–/I3 – electrolyte, long-term performance of MCSSC is achieved. Furthermore, these one-electron redox mediators conclusively demonstrate the unique optical activity of clusters, with excitation-wavelength-dependent photocatalytic activity.