Monte Carlo-quantum mechanics study of the UV-visible spectrum of benzophenone in water

The ultraviolet-visible (UV-Vis) absorption spectrum of benzophenone is cha racterized by two broad bands associated to a weak n-pi* and a strong pi-pi * transition. The theoretical description of the solvatochromic shift is an interesting challenge because in solvents the n-pi* transition suffers a b lue shift whereas the pi-pi* band suffers a red shift. This solvatochromism of benzophenone in water is studied theoretically in the entire UV-Vis reg ion (up to 200 nm) using a combined Monte Carlo-quantum mechanics approach. The Liquid structures are generated by NVT Metropolis Monte Carlo, and sup ermolecules are generated for subsequent quantum mechanical INDO/CIS calcul ations. Long simulations and stable ensemble averages are used. The results are in good qualitative agreement with experiment. The n-pi* transition sh ifts toward the blue by +1170 cm(-1). The pi-pi* band is composed by severa l transitions. The most intense is calculated to shift toward the red by -1 330 cm(-1). (C) 2000 John Wiley & Sons, Inc.