The excited-state dynamics of 6,13-bis­(triisopropylsilylethynyl)­pentacene is investigated to determine the role of excimer and aggregate formation in singlet fission in high-concentration solutions. Photoluminescence spectra were measured by excitation with the evanescent wave in total internal reflection, in order to avoid reabsorption effects. The spectra over nearly two magnitudes of concentration were nearly identical, with no evidence for excimer emission. Time-correlated single-photon counting measurements confirm that the fluorescence lifetime shortens with concentration. The observed rate constant grows at high concentrations, and this effect is modeled in terms of the hard-sphere radial distribution function. NMR measurements confirm that aggregation takes place with a binding constant of between 0.14 and 0.43 M–1. Transient absorption measurements are consistent with a diffusive encounter mechanism for singlet fission, with hints of more rapid singlet fission in aggregates at the highest concentration measured. These data show that excimers do not play the role of an emissive intermediate in exothermic singlet fission in solution and that, while aggregation occurs at higher concentrations, the mechanism of singlet fission remains dominated by diffusive encounters.

There is a need for improved nanomaterials to simultaneously target cancer cells and avoid nonspecific clearance by phagocytes. We developed an ellipsoidal polymersome system with a unique tunable size and shape property. These particles were functionalized with our in-house phage-display cell-targeting peptide to target a medulloblastoma cell line in vitro. Particle association with medulloblastoma cells was modulated by tuning the peptide ligand density on the particles. These polymersomes had low levels of association with primary human blood phagocytes. The stealth properties of the polymersomes were further improved by including the peptide targeting moiety, an effect that was likely driven by the peptide protecting the particles from binding blood plasma proteins. Overall, this ellipsoidal polymersome system provides a promising platform to explore tumor cell targeting in vivo.

Peptide-functionalized nanoparticles combine the best of both; the ability of nanoparticles to deliver a drug "cargo" throughout the body and the ability of peptides to selectively target certain cell types or biological systems. The vast majority of peptide-functionalized nanoparticles employ only one type of peptide, however, to truly realize the potential of these systems in medicine, nanoparticles equipped with two or even more peptide functionalities are desirable. In this review, the latest developments in dual-peptide functionalized nanoparticles are discussed. These are categorized depending on their structure; first broadly into grafted and selfassembled dual-peptide-nanoparticles with the former then subdivided further into nonconjugated, linearly conjugated and branched conjugated dual-peptide functionalized nanoparticles. These different categories of dual-peptide nanoparticles are then discussed with regards to the type of functional peptides used and their role in selective targeting nanomedicine.