This tutorial review deals with the methodological procedures that can be used to obtain accurate molecular sizes in solution from diffusion NMR spectroscopy. The critical aspects associated with the estimation of the size of molecules from the measured translational self-diffusion coefficient, using the Stokes-Einstein equation, are highlighted and discussed. From a theoretical point of view, it is shown how to take into account the size of the solute with respect to that of the solvent and its non-spherical shape using the appropriate correction factors in the frictional coefficient. From a practical point of view, the advantages of introducing an internal standard in the sample are presented. Initially, non-aggregating systems are considered in an attempt to clarify what hydrodynamic dimensions mean. Successively, aggregating systems are addressed showing how it is possible to understand the aggregation level and derive the thermodynamic parameters for some illustrative aggregation processes.

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The activity of three [Cp*IrL(n)] (Cp* = pentamethylcyclopentadienyl) archetypal catalysts ([Cp*Ir (bpy)Cl]Cl (1, bpy = 2,2'-bipyridine), [Cp*Ir(bzpy)(NO(3))] (2, bzpy = 2-benzoylpyridine) and [Cp*Ir(H(2)O)(3)](NO(3))(2) (3)) for water oxidation to molecular oxygen was compared using cerium(IV) ammonium nitrate as a sacrificial oxidant. Kinetic studies were carried out by: i) measuring the depletion of Ce(4+) through UV-Vis spectroscopy, ii) directly detecting the evolved oxygen through the Clark electrode and iii) measuring the volume of the evolved oxygen. The kinetics of Ce(4+) consumption were zero-order in Ce(4+) for catalysts 2 and 3, while they were first-order for 1. The order with respect to catalyst was 1 for 1 and 2 while it was 1.5 for 3. As a consequence, 2 (TOF(max) = 14.4 min(-1)) and 3 (TOF(max) = 50.4 min(-1)) were found to be the most active catalysts at low and high catalyst concentration, respectively, while the performance of 1 (TOF(max) = 8.6 min(-1)) increased with increasing the concentration of Ce4(+.) 1 and 3 were found to be the most robust catalysts at low (3.1 mu M, TON = 1240) and high (7.0 mu M, TON = 4042) catalyst concentration, respectively. In situ NMR studies were performed under exactly the same conditions of the catalytic experiments. It was observed that Cp* underwent an oxidative degradation, ultimately leading to acetic, formic and glycolic acids. Several Ir-containing intermediates of the degradation process were intercepted and fully characterized in solution through 1D- and 2D-NMR experiments. DFT and NMR studies indicated that the degradation proceeds via an initial double oxidative functionalization of both the quanternary carbon and proton of a Cp* C-CH(3) moiety

This contribution details the synthesis and chemical/physical characterization of a series of unconventional twisted pi-electron system electro-optic (EO) chromophores. Crystallographic analysis of these chromophores reveals large ring-ring dihedral twist angles (80-89 degrees) and a highly charge-separated zwitterionic structure dominating the ground state. NOE NMR measurements of the twist angle in solution confirm that the solid-state twisting persists essentially unchanged in solution. Optical, IR, and NMR spectroscopic studies in both the solution phase and solid state further substantiate that the solid-state structural characteristics persist in solution. The aggregation of these highly polar zwitterions is investigated using several experimental techniques, including concentration-dependent optical and fluorescence spectroscopy and pulsed field gradient spin-echo (PGSE) NMR spectroscopy in combination with solid-state data. These studies reveal clear evidence of the formation of centrosymmetric aggregates in concentrated solutions and in the solid state and provide quantitative information on the extent of aggregation. Solution-phase DC electric-field-induced second-harmonic generation (EFISH) measurements reveal unprecedented hyperpolarizabilities (nonresonant mubeta as high as -488,000 x 10(-48) esu at 1907 nm). Incorporation of these chromophores into guest-host poled polyvinylphenol films provides very large electro-optic coefficients (r(33)) of approximately 330 pm/V at 1310 nm. The aggregation and structure-property effects on the observed linear/nonlinear optical properties are discussed. High-level computations based on state-averaged complete active space self-consistent field (SA-CASSCF) methods provide a new rationale for these exceptional hyperpolarizabilities and demonstrate significant solvation effects on hyperpolarizabilities, in good agreement with experiment. As such, this work suggests new paradigms for molecular hyperpolarizabilities and electro-optics.