A priori calculations of the free energy of formation from solution of polymorphic self-Assembled monolayers

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Journal Article
Proceedings of the National Academy of Sciences of the United States of America, 2015, 112 (45), pp. E6101 - E6110
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Modern quantum chemical electronic structure methods typically applied to localized chemical bonding are developed to predict atomic structures and free energies for meso-Tetraalkylporphyrin self-Assembled monolayer (SAM) polymorph formation from organic solution on highly ordered pyrolytic graphite surfaces. Large polymorphdependent dispersion-induced substrate-molecule interactions (e.g., -100 kcal mol -1 to -150 kcal mol -1 for tetratrisdecylporphyrin) are found to drive SAM formation, opposed nearly completely by large polymorph-dependent dispersion-induced solvent interactions (70- 110 kcal mol -1 ) and entropy effects (25-40 kcal mol -1 at 298 K) favoring dissolution. Dielectric continuum models of the solvent are used, facilitating consideration of many possible SAM polymorphs, along with quantum mechanical/molecular mechanical and dispersion- corrected density functional theory calculations. These predict and interpret newly measured and existing high-resolution scanning tunnelling microscopy images of SAM structure, rationalizing polymorph formation conditions. A wide range of molecular condensed matter properties at room temperature now appear suitable for prediction and analysis using electronic structure calculations.
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