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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Density Functional Study of Excited Charge Transfer State Formation in 4-(N,N-Dimethylamino)benzonitrile
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Density Functional Study of Excited Charge Transfer State Formation in 4-(N,N-Dimethylamino)benzonitrile

机译：4-（N，N-二甲基氨基）苄腈中激发电荷转移态形成的密度泛函研究

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摘要

The excited singlet states of 4-(N,N-dimethylamino)benzonitrile (DMABN), 4-N,N-dimethylaminobenzaldehyd (DMABA), and methyl 4-N,N-dimethylaminobenzoate (DMABME) are studied by a combination of density functional theory and configuration interaction approaches (DFT/SCI). DMABN is investigated in more detail as the best known model system showing dual fluorescence in polar solvents. Because the origin of the second red-shifted fluorescence is still not steeled definitely, we consider three commonly discussed geometric relaxation pathways which generate low lying intramolecular charge transfer states (TICT, WICT, and RICT). In general, the results of the DFT/SCI calculations for excitation energies, oscillator strengths, and dipole moments compare favorably with either experimental results or data from very elaborate theoretical CASPT2 calculations. For DMABN we find a global minimum structure in the first excited state with a twisted (60°) but not pyramidalized dimethylamino group. The barrier for TICT state formation from the lowest 1B_2 state is computed to be 2.3 kcal/mol. The calculated vertical fluorescence band energy of 3.4 eV is in good agreement with experimental data (3.2 eV). The rehybridization of the cyano group according to the RICT model leads also to an excited-state minimum with strong charge-transfer character. However, this RICT state lies higher in energy than the TICT state and is furthermore associated with a large barrier (17.6 kcal/mol). The results of the DFT/SCI calculations for the keto derivatives DMABA and DMABME reveal, in agreement with experiment, quite a small splitting between the lowest L_b and L_a states (≈0.15 eV).
机译：通过密度泛函研究了4-（N，N-二甲基氨基）苄腈（DMABN），4-N，N-二甲基氨基苯甲醛（DMABA）和4-N，N-二甲基氨基苯甲酸甲酯（DMABME）的激发单重态理论和配置交互方法（DFT / SCI）。 DMABN作为最著名的模型系统进行了更详细的研究，该系统显示了极性溶剂中的双重荧光。由于第二个红移荧光的起源仍然不确定，因此我们考虑了三个经常讨论的几何弛豫途径，它们会产生低分子内电荷转移状态（TICT，WICT和RICT）。通常，DFT / SCI计算得出的激励能量，振荡器强度和偶极矩的结果，无论是实验结果还是非常精细的CASPT2理论计算的数据，都具有优势。对于DMABN，我们在第一个激发态中发现了一个整体最小结构，该结构具有扭曲的（60°）而不是金字塔状的二甲基氨基。从最低的1B_2状态形成TICT状态的势垒经计算为2.3 kcal / mol。计算得到的垂直荧光带能量为3.4 eV，与实验数据（3.2 eV）吻合良好。根据RICT模型，氰基的再杂化也导致具有强电荷转移特性的激发态最小值。但是，该RICT状态的能量高于TICT状态，并且与较大的势垒（17.6 kcal / mol）有关。酮基衍生物DMABA和DMABME的DFT / SCI计算结果表明，与实验一致，最低的L_b和L_a状态（≈0.15eV）之间有很小的差异。

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