n-Type 1D nanostructures are formed from the beta-sheet assembly of dipeptides bearing a 1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI) side chain into either helical nanofibers or twisted nanoribbons. Amyloid-like 1-D helical nanofibers and twisted nanoribbons assemble in an aqueous solution depending on the placement of the NDI group. beta-Sheet-type hydrogen bonding and pi-pi association play important roles in directing the assembly process. A delicate balance between electrostatic repulsion and hydrophobic interactions is critical for self-assembly. Fluorescence lifetime and anisotropy experiments indicate that the nature of the intermolecular organization and packing within the nanostructures critically impacts intermolecular energy migration pi-electron delocalization.

No abstract

Four free-base corroles with electron-donating or electron-withdrawing groups on the para or 2 through 6-positons of the meso phenyl rings were prepared via either Paolesse or Gross conditions and investigated for their absorption and emission properties. The triaryl corroles 5,10,15-triphenylcorrole, 5,10,15-tris(pentafluorophenyl)corrole, 5,10,15-tris(p-nitrophenyl)corrole, and 5,10,15-tris(p-methoxyphenyl)corrole were examined. Absorption, steady-state, and time-resolved fluorescence measurements were performed on all compounds in both nonpolar (dichloromethane) and polar (dimethylacetamide) solvents. The experimental evidence points to hydrogen bonding with an internal N-H group as the most likely factor in the solvent-dependent photophysical behavior of these corroles, that is also highly dependent upon substitution.

We report the photophysical characterization of the two tautomers (1e and 1i) of 5,10,15,20-tetraphenyl N-confused free-base porphyrin, potential building blocks in assemblies designed for artificial photosynthesis, using a combination of steady state and time-resolved techniques. Tautomer 1e was found to have a significantly higher quantum yield of fluorescence than tautomer 1i (Φ Fl ) 0.036 vs Φ Fl ) 0.0016, respectively), despite the fact the fluorescence lifetimes were quite similar (i.e., 1.98 ns vs 1.60 ns, respectively). These differences were attributed to a more rapid rate of internal conversion or intersystem crossing in 1i due to steric conditions in the interior of the macrocycle. The absorption spectra of these porphyrins were also examined using the results from B3LYP/6-31G(d)//B3LYP/3-21G(d) calculations and interpreted using the four electron four orbital model.

No abstract