Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo 1, Tarragona 43 007, Spain.
Aix-Marseille Univ, CNRS, ICR, Marseille 13 397, France.
J Am Chem Soc. 2021 Dec 29;143(51):21474-21477. doi: 10.1021/jacs.1c07039. Epub 2021 Dec 14.
Most aromatic ketones containing first-row elements undergo unexpectedly fast intersystem crossing in a few tens of picoseconds and a quantum yield close to unity. Among them, xanthone (9-xanthen-9-one) possesses one of the fastest singlet-triplet rates of only ∼1.5 ps. The exact mechanism of this unusually fast transition is still under debate. Here, we perform wavepacket dynamics of the photochemistry of xanthone in the gas phase and in polar solvents. We show that xanthone follows El-Sayed's rule for intersystem crossing. From the second singlet excited state, the mechanism is sequential: (i) an internal conversion between singlets ππ* → nπ* (85 fs), (ii) an intersystem crossing nπ* → ππ* (2.0 ps), and (iii) an internal conversion between triplets ππ* → nπ* (602 fs). Each transfer finds its origin in a barrierless access to electronic state intersections. These intersections are close to minimum energy structures, allowing for efficient transitions from the initial singlet state to the triplets.
大多数含有第一行元素的芳香酮在几十皮秒内经历异常快速的系间窜越，量子产率接近 1。其中，呫吨酮（9-呫吨-9-酮）具有最快的单重态-三重态速率之一，仅约 1.5 皮秒。这种异常快速跃迁的确切机制仍存在争议。在这里，我们在气相和极性溶剂中进行了呫吨酮光化学反应的波包动力学研究。我们表明，呫吨酮遵循 El-Sayed 的系间窜越规则。从第二单重激发态开始，机制是顺序的：（i）单重态ππ*→nπ之间的内转换（85 fs），（ii）nπ→ππ之间的系间窜越（2.0 ps），以及（iii）三重态ππ→nπ*之间的内转换（602 fs）。每个转移都源于对电子态交叉的无势垒进入。这些交叉点接近最低能量结构，允许从初始单重态到三重态的有效跃迁。
