Electronic polarization of 1H-benzotriazole in water: Ground and first excited-state dipole moments

Sequential Monte Carlo and quantum mechanical calculations of the electronic polarization of the ground and first vertical excited states of 1H-benzotriazole in water are made. Using statistically uncorrelated configurations and CASSCF ab initio calculations the increase in the ground and excited state dipole moments of lH-benzotriazole from gas phase to aqueous environment are obtained as 2.89 +/- 0.10 and 2.75 +/- 0.11 D, leading to total moments of 6.89 +/- 0.10 and 6.40 +/- 0.11 D, respectively. Structures are sampled using the statistical correlation interval obtained from the autocorrelation function of the energy and statistical convergence of the calculated dipole moments is shown. These water-polarized dipole moments of 1H-benzotriazole are used to obtain the solvatochromic shift of the first absorption transition. The resulting theoretical blue shift of 570 cm(-1) for the strong and characteristic pi --> pi* transition is in good agreement with the inferred experimental value of similar to700 cm(-1). The use of the gas-phase values of the dipole moments are useful for the qualitative understanding of the shift but the polarization of the solvent is required to achieve quantitative agreement. (C) 2003 Wiley Periodicals, Inc.