The photophysical properties of the Schiff base family are crucial for their applications such as molecular switches and molecular memories. However, it was found that the photophysical behavior is not uniform for all Schiff base molecules, which shows a significant substituent dependent property. In this article, we studied the photoisomerization mechanism of one Schiff base chlorosubstituted derivative 2-(1-(methylimino)methyl)-6-chlorophenol by employing geometrical optimization, energy profiles scanning, and on-the-fly dynamical simulations. Three types of minimum energy conical intersections were located on the S₁/S₀ crossing seam, with two characterized by twisting motion of the C=N bond and one featured with the excited state intramolecular proton transfer process and then twisting motion around the C=C bond [excited-state intramolecular proton transfer process (ESIPT)-then-twisting]. By a combination of the dynamics simulation results with the energy profiles scanned along with the ESIPT coordinate, it was found that the photophysical property of the targeted molecule is different from that of most Schiff base members, which prefer to decay by a twisting motion around the C=N bridge bond rather than the ESIPT-then-twisting channel. The minor ESIPT channel is probably governed by a tunneling mechanism. The proposed deactivation mechanism can provide a reasonable explanation for the observations in the experiment and would provide fundamental indications for further design of new and efficient photochromic products.

中文翻译：

---

2-（1-（甲基亚氨基）甲基）-6-氯酚（SMAC）的光诱导异构化机理：非绝热表面跳跃动力学模拟

Schiff碱基家族的光物理性质对其应用（例如分子开关和分子存储器）至关重要。然而，发现所有席夫碱分子的光物理行为不是均匀的，这显示出显着的取代基依赖性。在本文中，我们通过几何优化，能谱扫描和动态动力学模拟研究了一种席夫碱氯取代衍生物2-（1-（甲基亚氨基）甲基）-6-氯苯酚的光异构化机理。三种最小能量圆锥形交叉点位于S ₁ / S _0上跨接缝，其中两个特征在于C = N键的扭曲运动，另一个特征在于具有激发态的分子内质子转移过程，然后围绕C = C键发生扭曲运动[激发态分子内质子转移过程（ESIPT）-然后-扭曲]。通过将动力学模拟结果与扫描的能量分布以及ESIPT坐标相结合，发现目标分子的光物理性质与大多数席夫碱成员不同，后者更喜欢通过围绕基团的扭转运动而衰减。 C = N桥键，而不是ESIPT-然后扭曲通道。次要ESIPT通道可能由隧道机制控制。