Institut für Chemie und Biochemie, Physikalische und Theoretische Chemie , Freie Universität Berlin , Takustr. 3 14195 Berlin , Germany.
J Phys Chem B. 2019 Mar 14;123(10):2203-2209. doi: 10.1021/acs.jpcb.8b09841. Epub 2019 Mar 1.
We propose the ultrafast S (1B) to S (2A) "electronic internal conversion" observed in carotenoids to be a vibrational relaxation of the 1B state. This suggestion arises from comparing excited-state geometries computed with the CAM-B3LYP density functional to the ground states; it is found that each conjugated atom moves less than 5 pm in, for example, violaxanthin. However, the changes of excitation energies are large, ranging from 0.4 to 1.2 eV. This is connected to the size of the conjugated system: while each atom contributes only 0.02-0.06 eV, the sum amounts to the observed shift. Additional analysis of computational data is provided from new or already published calculations. As the mechanism may be valid for all linear polyenes, the model has implications that go beyond the presented case of carotenoids. Finally, four sets of experimental data on carotenoids published elsewhere are reinterpreted. The model predicts near-infrared (IR) absorptions and transient femtosecond IR spectra within 0.1 eV accuracy.
我们提出，在类胡萝卜素中观测到的超快 S（1B）到 S（2A）“电子内转换”是 1B 态的振动弛豫。这一建议源于将用 CAM-B3LYP 密度泛函计算得到的激发态几何形状与基态进行比较；结果发现，例如，在紫黄质中，每个共轭原子的移动距离小于 5 pm。然而，激发能的变化很大，范围从 0.4 到 1.2 eV。这与共轭体系的大小有关：虽然每个原子仅贡献 0.02-0.06 eV，但总和达到了观察到的位移。从新的或已发表的计算中提供了对计算数据的额外分析。由于该机制可能适用于所有线性聚烯，因此该模型的意义超出了呈现的类胡萝卜素案例。最后，重新解释了其他地方发表的关于类胡萝卜素的四组实验数据。该模型在近红外（IR）吸收和瞬态飞秒 IR 光谱方面的预测精度达到 0.1 eV。
