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Effect of solute flexibility and polarization on the solvatochromic shift of a brominated merocyanine dye in water: A sequential MD/QM study



A sequential molecular dynamics/quantum mechanics (MD/QM) procedure was used to investigate the effects of solute polarization and flexibility on the solvatochromism of a brominated merocyanine dye (MeBM) in water. Relevant structures for the solution were generated using MD simulations. The structural analysis indicates that the flexibility of MeBM is limited; showing small amplitudes both for dihedral isomerization and for the angle formed between the normal vectors of the pyridine and phenolate rings. The solvatochromic shift in the π–π* electronic transition was studied using both the PM6/CI and PM6/CI/COSMO methods in the gas phase as well as in the solution phase (solute + first solvation shell). The results obtained with the use of the hybrid polarizable continuum model/discrete description are in good agreement with available experimental values and indicate that the polarization of the solute plays a more significant role in the solvatochromism of MeBM than its flexibility. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010