Explicit solvent DRF INDOs/CIS computations of charge transfer state energetics in a pyrenyldeoxyuridine nucleoside model

被引:9
作者
Van Duijnen, PT
Netzel, TL
机构
[1] Georgia State Univ, Dept Chem, Atlanta, GA 30302 USA
[2] Univ Groningen, Ctr Mat Sci, NL-9747 AG Groningen, Netherlands
关键词
D O I
10.1021/jp0542221
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
In this work we present calculated absorption and emission spectra in acetonitrile (MeCN) solution of N-acetyl-1-aminopyrene (PAAc, a spectroscopic model compound) and N-(1-pyrenyl)-1-methyluracil-5-carboxamide (PAU(Me), a computational model for 5-(N-carboxyl-1-aminopyrenyl)-2'-deoxyuridine (PAdU)). The computational method used-the discrete reaction field approach (DRF)-combines a quantum mechanical (QM) description of the solute (here DFT and INDOs/CIS, i.e., the INDO parametrization for spectroscopy) with a classical, molecular mechanics (MM) description of the solvent molecules. The latter are modeled with point charges representing the permanent charge distribution and polarizabilities to account for many-body interactions among the solute and other solvent molecules. Molecular dynamics is used to sample the degrees of freedom of the solution around several solute conformations each in two electronic excited states. This leads to a large number of solute/solvent configurations from which 800 are selected for each excited state and collected into a single ensemble by means of proper Boltzmann averaging. DRF INDOs/CIS applied to the selected solute/solvent configurations give simulated absorption and emission band spectra-each based on 15200 calculated transitions-that compare well with experimental results. For example, the much broader absorption and emission bands in PAdU compared with PAAc are reproduced, and the simulated emission spectra of PAU(Me) agree well with broad (380-550 nm) charge transfer (CT) emission seen for PAdU in MeCN. The observed multiexponential fluorescence decay profiles for PAdU in different polar solvents are interpreted in terms of solute/solvent conformational heterogeneity here generated in the MD simulations for PAUMe in MeCN. Additionally, the simulations demonstrate the mixing of the forbidden Py center dot+/dU(center dot-) CT states with allowed pyrenyl (1)(pi,pi*) states.
引用
收藏
页码:2204 / 2213
页数:10
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