A Two-Response-Time Model Based on CM2/INDO/S2 Electrostatic Potentials for the Dielectric Polarization Component of Solvatochromic Shifts on Vertical Excitation Energies

Li, J.; Cramer, C. J.; Truhlar, D. G.
Int. J. Quantum Chem. 2000, 77, 264.

A model is presented for the electrostatic component of solvatochromic shifts on vertical electronic excitation energies. The model, called Vertical Electrosatic Model 42 (VEM42), is based on representing the solute by a set of distributed atomic monopoles obtained by Charge Model 2 (CM2) and representing the solvent by its static and optical dielectric constants. The theory is applied here with Intermediate Neglect of Differential Overlap for Spectroscopy-Parameterization 2 (INDO/S2) configuration interaction wave functions. The model is implemented in the ZINDO electronic-structure-code package. We present illustrative applications to the singlet n-->pi* excitation of acetone in nine solvents. When the electrostatics are augmented by one-parameter estimates of dispersion and hydrogen bonding contributions, the experimental solvatochromic shifts in the nine solvents are reproduced with a mean unsigned error of 65 cm^-1 (0.2 kcal/mol). These calculations present a compelling picture of the quantitative origin of the solvatochromic red and blue shifts in this prototype n-->pi* excitation.

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