Pyrene-Labeled Poly(aryl ether) Monodendrons:  Synthesis, Characterization, Diffusion Coefficients, and Photophysical Studies

Four generations of poly(aryl ether) monodendrons labeled with pyrene at the focus were synthesized and characterized by a combination of NMR, size-exclusion chromatography with light scattering detection, and electronic spectroscopy. The monodendrons were then studied by magnetic resonance and fluorescence techniques. Translational diffusion coefficients in THF-d8, acetonitrile-d3, and cyclohexane-d12 were measured by pulsed-field-gradient NMR and ranged from 2.2 × 10-5 cm2/s for methoxypyrene in acetonitrile to 3.4 × 10-6 cm2/s for the fourth generation monodendron in THF. Molecular radii were calculated from the diffusion coefficients by the Stokes−Einstein equation. In THF, the radii increased from 2.8 A for methoxypyrene to 14 A for the fourth generation monodendron. In acetonitrile the radii were smaller, increasing from 2.7 A for methoxypyrene to 5.4 A for the third generation monodendron. In both solvents, a change in solution structure between the second and third generation monodendrons was obse...