Unusual Fluorescence Behavior of Pyrene-Amine Containing Dendrimers.

A new class of pyrene-based dendrimers, characterized by the presence of a 1,4,7,10-Tetraazacyclododecane (cyclen) unit as the core, was studied by SSF (steady-state fluorescence) and SPC (single-photon counting fluorescence). The photophysical behavior of these dendrimers was studied in THF, DMF and DMSO solution. The typical signals for pyrene-labeled molecules were recorded in each solvent, showing the representative fluorescence spectra: the corresponding emissions of monomer and excimer of the pyrene chromophore are observed. Unexpectedly, the typical quenching of tertiary amine on the pyrene emission was not observed in these dendrimers. Quenching studies were performed by adding up to 3 equivalents of trifluoroacetic acid (TFA). To our knowledge, this is the first report of pyrene's unquenching behavior by a tertiary amine.

Synthesis and photophysical properties of novel pyrene-metalloporphyrin dendritic systems.

A novel series of dendronized porphyrins bearing pyrene units in the periphery (Porph-O-Gn) and their metal complexes (M-[Porph-O-Gn]) are reported. The pyrene-containing Frechet-type dendrons up to the first generation were synthesized and further reacted with 5-phenol-10,15,20-triphenylporphyrin via an esterification reaction to afford the desired pyrene-labeled dendronized porphyrins. Later, these compounds were used as ligands to produce the corresponding complexes of Zn2+, Cu2+, Mg2+ and Mn3+. With the compounds in hand, the optical and photophysical properties of the dendritic metalloporphyrins were studied by absorption and fluorescence spectroscopy. The quantum yields, Förster radius and efficiency of energy transfer were determined and discussed as a function of the structure and the donor-acceptor distances, finding an efficient energy transfer from the pyrene moiety to the metallated porphyrin core in each case.