K W Hipps - A Single Molecule Level Study of the Temperature-Dependent Kinetics for the Formation of Metal Porphyrin Monolayers on Au(111) from Solution

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      Publication Details (including relevant citation   information):

      Bhattarai, Ashish, Mazur, Ursula, Hipps, K. W. Journal of the   American Chemical Society 2014 136  (5) 2142-2148

      Abstract: Scanning tunneling microscopy was used   to make the first molecular scale measurements of the temperature   dependence of composition of an adlayer at the solution–solid   interface. We conclusively demonstrate that metal porphyrins   adsorb very strongly on Au(111) at the solution solid interface   such that the monolayer composition is entirely kinetically   controlled below about 100 °C. The barrier for desorption is so   great in fact that a temperature of 135 °C is required to induce   desorption over a period of hours. Moreover, cobalt(II)   octaethylporphyrin (CoOEP) and NiOEP desorb at different rates   from different sites on the surface. We have measured the rate   constant for desorption of CoOEP into phenyloctane to be 6.7 ×   10–5/s at 135 °C. On the basis of these measurements, an upper   bound can be set for the desorption rate of NiOEP into   phenyloctane as 6.7 × 10–4/s at 135 °C. For solutions of the   order of 100 μM in NiOEP or CoOEP, a dense monolayer is formed   within seconds, and the adsorption rate constants fall within 40%   of each other. The structures of NiOEP and CoOEP monolayers are   essentially identical, and the molecular spacing for both can be   described by A = 1.42 ± 0.02 nm, B = 1.32 ± 0.02 nm, and α = 57°   ± 2°. The solubility of CoOEP and NiOEP in phenyloctane at room   temperature was measured to be 0.228 and 0.319 g/L, respectively.

      Address (URL): http://dx.doi.org/10.1021/ja412648x