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-d 8, acetonitrile-d3, and cyclohexane-d12 were measured by pulsed-field-gradient NMR and ranged from 2.2 × 10 -5 cm 2 /s for methoxypyrene in acetonitrile to 3.4 × 10 -6 cm 2 /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 Å for methoxypyrene to 14 Å for the fourth generation monodendron. In acetonitrile the radii were smaller, increasing from 2.7 Å for methoxypyrene to 5.4 Å for the third generation monodendron. In both solvents, a change in solution structure between the second and third generation monodendrons was observed in the diffusion data. The rate of fluorescence quenching by molecular oxygen was measured for the pyrene-labeled monodendrons in THF, acetonitrile, and cyclohexane and was found to decrease for monodendrons of increasing generation. This decrease cannot be fully explained by the slower diffusion of the larger monodendrons. Several simple models for the reduced quenching rate of the pyrene chromophore were developed. These models suggest that the increased density of the larger monodendrons provides a more effective barrier to diffusing dioxygen.

Key indicators: single-crystal X-ray study; T = 100 K; mean (C-C) = 0.003 Å; R factor = 0.016; wR factor = 0.040; data-to-parameter ratio = 17.3.In the title compound, [RuCl 2 (C 4 H 4 N 2 ) 4 ]Á2CH 2 Cl 2 , the Ru II atom occupies a position of 222 symmetry and the C atom of the solvent molecule occupies a site with twofold symmetry. The Ru II atom has a slightly distorted octahedral geometry. The pyrazine rings are propeller-like and rotated 45.1 (1) from the RuN 4 plane. In the crystal, the complex and solvent molecules are bridged by weak C-HÁ Á ÁN hydrogen bonds along the c axis. Weak intermolecular C-HÁ Á ÁCl contacts link the complexes in the ab plane, forming a network. Related literatureThe synthesis of the title complex and its use as a building block in coordination networks are described by Carlucci et al. ExperimentalCrystal data [RuCl 2 (C 4 Table 1 Hydrogen-bond geometry (Å , ). We thank Austin College (Cullen Funds) for supporting innovative undergraduate education and the Welch Foundation (AD-0007) for a chemistry department grant furthering undergraduate research. We also recognize the work of Jessie H. Berger, Tehreem Bilal, Michela L. Brumfield, Raven M. Clark, Edward J. Selvik, Jacob B. Smith, and Hans H. Yoon, who, as fellow students with WK and AER in an advanced inorganic lab, synthesized and attempted to grow crystals of the title compound.