SUPORTING INFORMATION The Cathodic Voltammetric Behavior of Pillar[5]quinone in Nonaqueous Media. Symmetry Effects on the Electron Uptake Sequence.

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1 SUPORTING INFORMATION The Cathodic Voltammetric Behavior of Pillar[5]quinone in Nonaqueous Media. Symmetry Effects on the Electron Uptake Sequence. Beijun Cheng and Angel E. Kaifer* Department of Chemistry and Center for Supramolecular Science, University of Miami, Coral Gables, FL , USA. TABLE OF CONTENTS Page Experimental Section Sample ln(i/io) vs G 2 plots Cyclic Voltammetry of P5Q Derivation of equations 4 and 5 S2- S3 S4 S5 S5- S7 Page S1

2 1. Experimental Section Synthesis. Pillar[5]quinone was synthesized as reported by Shivakumar and Sanjayan. 1 All other chemicals were commercially available and used without further purification. Electrochemical experiments. A single compartment glass cell was used for all voltammetric experiments. Typically the cell was fitted with a glassy carbon working electrode (0.071 cm 2 ), a platinum auxiliary electrode, a Ag/AgCl reference electrode and nitrogen inlet Teflon tubing. Nitrogen gas was purified before use and bubbled through the solution to remove dissolved oxygen before the measurements. During the voltammetric measurements, nitrogen flow was maintained above the solution to minimize re- dissolution of oxygen. The working electrode was polished on a soft, felt surface, using aqueous alumina (0.05 µm) slurries. Before each use the working electrode surface was rinsed extensively with water and sonicated to remove any particulate left from polishing. The square wave voltammetric experiments were run with a step potential of 4 mv, pulse amplitude of 25 mv and 15 Hz of frequency. The normal pulse voltammetric experiments were run at a scan rate of 100 mv/s, a sample width of 17 ms and a pulse width of 50 ms. NMR Diffusion Measurements. 1 H PGSE NMR measurements were performed by using the standard stimulated echo pulse sequence on a Bruker 400 MHz spectrometer at 300 K without spinning. The shape of the gradients was rectangular, their duration (δ) was 4 ms, and their strength (G) was varied during the experiments. The delay between gradient pulses was 54 ms. All spectra were Page S2

3 recorded on a spectrometer equipped with a GAB z- gradient unit capable of producing magnetic pulsed field gradients in the z- direction up to 0.50 T/m. The semi- logarithmic plots of ln(i/i0) vs G 2 were fitted using Office Excel software; the R factor was always higher than The dependence of the resonance intensity (I) on a constant diffusion time and on a varied gradient strength (G) is described by eq. S1: ln (I/I0) = - (γδ) 2 D (Δ δ/3) G 2 (S1) where I is the intensity of the observed spin- echo, I0 is the intensity of the spin- echo without gradients, D is the diffusion coefficient, Δ is the delay between the midpoints of the gradients, δ is the length of the gradient pulse and γ is the gyromagnetic ratio. Illustrative examples are shown in Figure S1 and S2. References (1) Shivakumar, K. I.; Sanjayan, G. J. Synthesis 2013, 45, 896. Page S3

4 Figure S1. Normalized signal decay as a function of gradient strength for XQ in CD2Cl2. Figure S2. Normalized signal decay as a function of gradient strength for P5Q in CD2Cl2. Page S4

5 Figure S3. Cyclic voltammetric behavior on glassy carbon (0.071 cm 2 ) of 1.0 mm P5Q in dichloromethane solution also containing 0.1 M TBAPF6. Scan rate: 0.1 V s - 1. Derivation of equation 4 in the manuscript In normal pulse voltammetry (NPV) the limiting (diffusional) current is given by the following equation: i d = nfad 1/2 * o C o 1/2 (eq. S1) τ τ ' π 1/2 ( ) where n is the number of electrons involved in the electrochemical process, F is Faraday s constant, A is the projected (geometric) area of the electrode, Do is the diffusion coefficient of the electroactive species, Co * is its bulk concentration and τ and τ specify the timing of current measurements during the pulse sequence. Let us consider two different species, XQ and P5Q, with different diffusion coefficients, DXQ and DP5Q, and different numbers of exchanged electrons, nxq and np5q, respectively. If we prepare a solution for each compound having the same bulk concentration, Co *, Page S5

6 and use the same electrode (same A) and NPV time parameters (τ and τ ) and pulse sequence, the measured limiting currents will be given by the following two equations: (i d ) XQ = (n )FA(D XQ XQ )1/2 * C o (eq. S2) π 1/2 (τ τ ') 1/2 (i d ) P5Q = (n )FA(D P5Q P5Q )1/2 * C o (eq. S3) π 1/2 (τ τ ') 1/2 Therefore, these two equations can be combined to give: * FAC o π 1/2 (τ τ ') = (i d ) XQ 1/2 (n XQ )(D XQ ) = (i d ) P5Q (eq. S4) 1/2 1/2 (n P5Q )(D P5Q ) which is identical to eq. 4 in the manuscript. Derivation of equation 5 in the manuscript For two sets of experimental conditions, denoted with the subscripts 1 and 2, the Stokes- Einstein equation leads to (D o ) 1 η 1 = (D o ) 2 η 2 (eq. S5) where Do stands for the diffusion coefficient and η is the medium viscosity. We measured the viscosity of the two media used (CD2Cl2 and CH2Cl2 containing 0.1 M tetrabutylammonium hexafluorophosphate) using an Ostwald viscometer, in which the viscosity is calculated as η = Bρt (eq. S6) where B is a calibration constant, ρ is the density and t is the measured flow time in the viscometer. Combining equations S5 and S6 yields (D o ) 1 = D o ( ) 2 ρ 2 t 2 ρ 1 t 1 (eq. S7) Page S6

7 Using the measured densities of the NMR solvent (CD2Cl2) and the electrochemistry solvent (0.1 M TBAPF6/CH2Cl2), and g/ml, and the experimentally measured flow times, 24.2 and 25.9 sec, respectively, we obtain ( D o ) EChem = 0.959( D o ) NMR (eq. S8) which is identical to eq. 5 in the manuscript and allows the calculation of the Do values under electrochemical conditions from the Do values measured in the NMR spectroscopic experiments. Page S7