Molecular composites were prepared by solubilizing pyrene in diaminobutane poly(propyleneimine) dendrimers having 32 or 64 primary amine end groups À1 by fluorescence spectroscopy. Fluorescence studies were also employed to probe the release of pyrene from the interior of dendrimers as a function of pH. When the pH value of the system was decreased from pH 11 by addition of HCl, the fluorescence intensity of the system was found to increase by approximately tenfold at pH 2 ± 4. In addition, at pH 2, the ratio of the first to the third vibrational peak of pyrene (I 1 /I 3 ) increased from 0.9, the value typical for pyrene solvated in dendrimer solution, to 1.60, the value characteristic of pyrene in water. Pyrene release from the interior of dendrimers was confirmed by fluorescence quenching when sodium iodide was added, since NaI does not affect the emission of dendrimer-solubilized pyrene. Finally, fluorescence quenching was used to locate the solubilization sites of pyrene within the dendrimer microcavities. These sites are close to the core of the dendrimer, near the tertiary amino groups which are also responsible for quenching the fluorescence of the dendrimer-bound pyrene.

The binding of fluorescent probe molecules to poly(amidoamine) starburst dendrimers of generations G-0, G-1, and G-2 was investigated. The solubilizing capability of these new materials, in aqueous media, increases with increasing degree of their generation. Pyrene fluorescence however undergoes significant quenching in the solubilized state. In the higher generations, G-1 and G-2, excimer fluorescence was observed even at [pyrene]/[dendrimer] ratios as low as 10-3.

Steady-state luminescence spectroscopy and luminescence decay analysis have been employed to study the association of two rare earth ions (i.e., Eu 3+ and Tb 3+ ) with poly-(ethylene glycol) in the absence and in the presence of 2,2′-bipyridine, which acted as an antenna of near-UV radiation. Three different systems have been studied at various polymer concentrations, i.e., aqueous solutions, transparent composite organic/inorganic sol-gel matrixes made by hydrolysis of tetramethoxysilane, and polymer matrixes. The photophysical behavior of the luminescent species has been studied in conjunction with the poly(ethylene glycol) content. In both aqueous solutions and silica matrixes, luminescence intensity and decay time were found to increase by increasing polymer concentration. Addition of 2,2′bipyridine resulted in complex formation between the ligand and the lanthanide ions. This complex was stabilized by association with the polymer chains. Excitation at the ligand absorption wavelength (337 nm) resulted in ligand-to-metal energy transfer and strong luminescence emission, characterized by the narrow-band emission of the metal. The complex between lanthanide ions and 2,2′-bipyridine possessed its own particular photophysical characteristics and emitted a bright broad blue luminescence with an excitation maximum around 380 nm. Freeze-drying of aqueous solutions of medium size poly(ethylene glycol) containing lanthanide ions and 2,2′-bipyridine produced an intensely luminescent solid material emitting the characteristic luminescence of the metal when excited at the ligand absorption band (337 nm) or the characteristic luminescence of the complex when excited at 380 nm.