Tatchen Jörg, Gilka Natalie, Marian Christel M
Institute of Theoretical and Computational Chemistry, Heinrich Heine University, Universitätsstr. 1, D-40225 Düsseldorf, Germany.
Phys Chem Chem Phys. 2007 Oct 14;9(38):5209-21. doi: 10.1039/b706410a.
For 7H-furo[3,2-g][1]benzopyran-7-one (psoralen), intersystem crossing (ISC) rate constants have been computed. Employing the Fermi golden rule, the harmonic approximation, and a pure-spin Born-Oppenheimer basis, both direct and vibronic spin-orbit (SO) coupling has been taken into account. Necessary data on electronic excitation energies and potential energy hypersurfaces originate from correlated all-electron calculations applying (time-dependent) density functional theory and the density functional theory/multireference configuration interaction approach. SO coupling has been treated by means of the one-center mean-field approximation. Vibronic SO couplings have been evaluated via numerical differentiation of SO matrix elements. Accounting only for direct SO coupling, rate constants of the order of k(ISC) approximately 10(10) s(-1) result for S2(n --> pi*) --> T1(pi --> pi*) ISC, whereas the rates of the channels S1 (pi --> pi*) --> {1,2 3} (pi --> pi*) do not exceed k(ISC) approximately 10(5) s(-1). Including vibronic SO coupling, rate constants of k(ISC) approximately 3 x 10(8) s(-1) are obtained for the S1 (pi --> pi*) --> T1 (pi --> pi*) ISC. The radiationless transition from the S1(pi --> pi*) state to the nearly degenerate T3(pi --> pi*) state has been estimated to be slightly less efficient (k(ISC) approximately 10(7) s(-1)). Based on our computed rates of ISC and excited state solvent shifts, we conclude that the experimentally observed appreciable triplet quantum yields of psoralen in polar protic media are primarily due to S1(pi --> pi*) --> T (pi --> pi*) channels. For heteroaromatic systems, (pi --> pi*)/(pi --> pi*) ISC driven by vibronic SO coupling is expected to be a common triplet state population mechanism.
对于7H-呋喃并[3,2-g][1]苯并吡喃-7-酮（补骨脂素），已经计算了系间窜越（ISC）速率常数。采用费米黄金规则、谐波近似和纯自旋玻恩-奥本海默基，同时考虑了直接和振动电子自旋-轨道（SO）耦合。关于电子激发能和势能超曲面的必要数据源自应用（含时）密度泛函理论以及密度泛函理论/多参考组态相互作用方法的相关全电子计算。SO耦合通过单中心平均场近似进行处理。振动电子SO耦合通过SO矩阵元的数值微分来评估。仅考虑直接SO耦合时，对于S2（n→π*）→T1（π→π*）ISC，得到的k（ISC）约为10^10 s^-1量级的速率常数，而S1（π→π*）→{1,2 3}（π→π*）通道的速率不超过k（ISC）约10^5 s^-1。包括振动电子SO耦合时，对于S1（π→π*）→T1（π→π*）ISC，得到的k（ISC）约为3×10^8 s^-1的速率常数。从S1（π→π*）态到近简并T3（π→π*）态的无辐射跃迁估计效率略低（k（ISC）约为10^7 s^-1）。基于我们计算的ISC速率和激发态溶剂位移，我们得出结论，在极性质子介质中实验观察到的补骨脂素可观的三重态量子产率主要归因于S1（π→π*）→T（π→π*）通道。对于杂芳族体系，由振动电子SO耦合驱动的（π→π*）/（π→π*）ISC预计是一种常见的三重态布居机制。
