We report solvatochromism in UV-visible spectra and quantum chemical simulations for a previously unconsidered stratification in reaction mixtures in the immediate vicinity of catalytic sites when at least one of the components of the fluid phase exhibits �epiphilicity� (defined as preferential segregation near the solid surface of the catalyst). Epiphilicity may occur in the upgrading of biomass-derived feedstocks into fuels, where polar as well as nonpolar liquids (e.g. water and the product fuel molecules) could stratify near the catalyst surface or near pore walls.We prepared soluble catalyst precursors containing luminescent chromophores, viz., a metal oxo-group attached to polyhedral oligomeric silsequioxane (POSS) clusters and we measured solvatochromic shifts of absorption and emission bands as a first step towards determining effects of intra-pore and near-surface environments on the structure and composition of the liquid phase adjacent to heterogeneous catalysts. We observed systematic shifts (h?A-h?E) in the absorbance and emission peaks of a site with changes in the polarizability (?f) of its environment and with changes in the dipole moment of the ground and excited states of the site (�E-�G) through the well-known Lippert relation. Such correlations have proved useful in biology and in rheology for probing compositional variations and fluid mobility at length scales of around 1 nm, comparable to what we envisage for stratification of multiphasic reaction medium in the pores of heterogeneous catalysts.Quantum chemical modeling captured the absorption and emission peak energies of unsolvated metal oxo chromophore. We will report how the trends in the calculated changes in dipole moments of the clusters associated with those electronic transitions track with the polarizability of the solvating media.The characterization technique explored here, when combined with QM/MD will detail local concentrations of reactants and products needed to devise accurate rate laws and to improve the design of catalysts surfaces.

Luminescence spectroscopy assesses the composition of the reaction medium neighboring a catalytic site

246th National Meeting (2013)

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