Solvatochromic Shifts:
A Combined QM/MM Configuration Interaction Approach.
| One of the powerful experimental techniques for probing
solute-solvent interactions is provided by the solvent dependence of UV/Vis absorption
spectra. Since polarities of the ground and excited state of a chormophore are
typically different, a change in the solvent polarity will lead to differential
stablization of the ground and excited states, and thus, a change in the energy gap
between these electronic states. Consequently, variations in the position,
intensity, and shape of the absorption spectra are direct measures of the specific
interactions between the solute and solvent molecules.
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An example of the hypsochromic shift of acetone on going from phase phase into water:
| We have developed a combined QM/MM configuration
interaction (CI) Monte Carlo simulation method for the predition of solvatochromic shifts
of chemical compounds in solution. The method is based on the treatment of the
solute molecule using a configuration interaction method either with single excited states
or multiple excited states. Then, Monte Carlo simulations are performed in the
presence of explicit classical or molecular mechanical solvent molecules to obtain the
excitaion spectra distribution and average. The CIS or full CI QM/MM calculations
can be carried out both at the semiempirical level or at the ab initio level. Computed Solvent Spectral Shifts for the n->pi* Electronic Transition of acetone (1/cm).
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| Method: J. Gao, J. Am. Chem. Soc. 116, 9324 (1994). Polarization: J. Gao, K. Byun, Theoret. Chem. Acc. 96, 151 (1997). Excited State pKa: J. Gao, N. Li, M. Freindorf, J. Am. Chem. Soc. 118, 4912 (1996).
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