Department of Applied Chemistry, Kyung Hee University, 1 Seochun-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do 446-701, Korea.
J Phys Chem A. 2011 Dec 1;115(47):13743-52. doi: 10.1021/jp207701r. Epub 2011 Nov 4.
The excited-state tautomerization of 7-azaindole (7AI) complexes bonded with either one or two methanol molecule(s) was studied by systematic quantum mechanical calculations in the gas phases. Electronic structures and energies for the reactant, transition state (TS), and product were computed at the complete active space self-consistent field (CASSCF) levels with the second-order multireference perturbation theory (MRPT2) to consider the dynamic electron correlation. The time-dependent density functional theory (TDDFT) was also used for comparison. The excited-state double proton transfer (ESDPT) in 7AI-CH(3)OH occurs in a concerted but asynchronous mechanism. Similarly, such paths are also found in the two transition states during the excited-state triple proton transfer (ESTPT) of the 7AI-(CH(3)OH)(2) complex. In the first TS, the pyrrole ring proton first migrated to methanol, while in the second the methanol proton moved first to the pyridine ring. The CASSCF level with the MRPT2 correction showed that the former path was much preferable to the latter, and the ESDPT is much slower than the ESTPT. Additionally, the vibrational-mode enhanced tautomerization in the 7AI-(CH(3)OH)(2) complex was also studied. We found that the excitation of the low-frequency mode shortens the reaction path to increase the tautomerization rate. Overall, most TDDFT methods used in this study predicted different TS structures and barriers from the CASSCF methods with MRPT2 corrections.
在气相中，通过系统的量子力学计算研究了与一个或两个甲醇分子键合的 7-氮杂吲哚（7AI）配合物的激发态互变异构化。在完全活性空间自洽场（CASSCF）水平上，使用二级多参考微扰理论（MRPT2）计算了反应物、过渡态（TS）和产物的电子结构和能量，以考虑动态电子相关。还使用了时间依赖密度泛函理论（TDDFT）进行比较。在 7AI-CH（3）OH 中的激发态双质子转移（ESDPT）以协同但非同步的机制发生。同样，在 7AI-（CH（3）OH）（2）配合物的激发态三质子转移（ESTPT）的两个过渡态中也发现了类似的路径。在第一个 TS 中，吡咯环质子首先迁移到甲醇，而在第二个 TS 中，甲醇质子首先迁移到吡啶环。带有 MRPT2 校正的 CASSCF 水平表明，前一条路径比后一条路径更可取，ESDPT 比 ESTPT 慢得多。此外，还研究了 7AI-（CH（3）OH）（2）配合物中的振动模式增强互变异构化。我们发现，低频模式的激发缩短了反应路径，从而提高了互变异构化速率。总体而言，本研究中使用的大多数 TDDFT 方法预测的 TS 结构和势垒与带有 MRPT2 校正的 CASSCF 方法不同。
