title: Role of dynamic flexibility in computing solvatochromic properties of dye-solvent systems: o-betaine in water.
abstract: Car-Parrinello molecular dynamics (CPMD) and Car-Parrinello mixed quantum mechanics/classical mechanics (CP-QM/MM) calculations were performed for o-betaine (OB) in the gas phase and water as solvent to study the solvent dependence on its molecular properties: geometry, charge distribution, and dipole moment. It is found that the molecular geometry in the gas phase is close to the planar structure, while in the water it is a twisted structure. The calculations clearly show that in both the gas phase and water the OB molecule is highly flexible with a large amplitude for the twist angle motion. The average gas-phase dipole moment for OB doubles in water, something that concords with a strong increase of total charge on phenoxide and pyridinium rings. We also investigated the solvatochromic shift in the pi-pi* and n-pi* transitions by carrying out INDO/CIS calculations for the gas-phase and solution-phase configurations obtained from the CPMD and CP-QM/MM calculations with results that are in good agreement with available experimental values (J. Chem. Soc., Perkin Trans. 2 1999, 1, 713). Our work indicates the importance of allowing full structural and dynamic flexibility of dye-solvent systems in predicting their basic solvatochromic properties.
authors.affiliation: Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden. murugan@theochem.kth.se
authors.forename: N Arul
authors.initials: NA
authors.lastname: Murugan
authors.forename: Hans
authors.initials: H
authors.lastname: Agren
mesh_terms: D001622:Betaine / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D005740:Gases; D008958:Models, Molecular; D009038:Motion; D018583:Pliability; D011789:Quantum Theory; D012996:Solutions; D012997:Solvents / Q000737:chemistry*; D014867:Water
chemical_list: D004396:Coloring Agents; D005740:Gases; D012996:Solutions; D012997:Solvents; D014867:Water; D001622:Betaine