State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, Liaoning, People's Republic of China.
J Comput Chem. 2014 Jan 15;35(2):109-20. doi: 10.1002/jcc.23463. Epub 2013 Nov 19.
This extensive theoretical study employed the spin-flip density functional theory (SFDFT) method to investigate the photoisomerization of 11-cis-retinal protonated Schiff base (PSB11) and its minimal model tZt-penta-3,5-dieniminium cation (PSB3). Our calculated results indicate that SFDFT can perform very well in describing the ground- and excited-state geometries of PSB3 and PSB11. We located the conical intersection (CI) point and constructed the photoisomerization reaction path of PSB3 and PSB11 by using the SFDFT method. To further verify the SFDFT results, we computed the energy profiles along the constructed linearly interpolated internal coordinate (LIIC) pathways by using high-level theoretical methods, such as the EOM-CCSD, CR-EOM-CCSD(T), CASPT2, NEVPT2, and XMCQDPT2 methods. The SFDFT method predicts that the photoisomerization of PSB3 is barrierless, in accordance with previous complete-active-space self-consistent-field (CASSCF) results. However, an energy barrier is predicted along the LIIC pathways of PSB11. This finding is different from previous CASSCF results and may indicate that the photoisomerization of PSB11 in gas phase is similar to that in solution. However, the higher spin contamination of the SFDFT method in the vicinity of the CI point caused the located CI geometry to deviate from that of the real CI. In addition, the LIIC pathways are only approximations to the minimum energy path (MEP). Thus, further experimental and theoretical studies are needed to verify the existence of an energy barrier along the photoisomerization reaction path of PSB11 in gas phase.
这项广泛的理论研究采用自旋翻转密度泛函理论（SFDFT）方法研究了 11-顺式视黄醛质子化席夫碱（PSB11）及其最小模型 tZt-戊-3,5-二烯亚胺阳离子（PSB3）的光致异构化。我们的计算结果表明，SFDFT 可以很好地描述 PSB3 和 PSB11 的基态和激发态几何形状。我们定位了锥形交叉（CI）点，并通过 SFDFT 方法构建了 PSB3 和 PSB11 的光致异构化反应路径。为了进一步验证 SFDFT 的结果，我们使用高理论水平的方法，如 EOM-CCSD、CR-EOM-CCSD(T)、CASPT2、NEVPT2 和 XMCQDPT2 方法，沿着构建的线性内坐标（LIIC）路径计算了能量分布。SFDFT 方法预测 PSB3 的光致异构化是无势垒的，这与之前的完全活性空间自洽场（CASSCF）结果一致。然而，在 PSB11 的 LIIC 路径上预测到了一个能垒。这一发现与之前的 CASSCF 结果不同，可能表明 PSB11 在气相中的光致异构化与在溶液中的光致异构化相似。然而，在 CI 点附近，SFDFT 方法的自旋污染较高，导致所定位的 CI 几何形状偏离了真实的 CI。此外，LIIC 路径只是对最低能量路径（MEP）的近似。因此，需要进一步的实验和理论研究来验证 PSB11 在气相中的光致异构化反应路径上是否存在能垒。
