Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
Phys Chem Chem Phys. 2011 May 21;13(19):8723-32. doi: 10.1039/c0cp02218g. Epub 2011 Feb 17.
The dual photochemistry of anthracene-9,10-endoperoxide (APO) was investigated in a fs UV pump-supercontinuum probe experiment, along with anthracene (AC) and anthraquinone (AQ) for comparison. Excitation of APO at 282 nm leads to 100% product formation by two competing photoreaction channels. Cycloreversion generates with a ∼25% quantum yield (QY) (1)O(2) and AC vibrationally excited in the singlet electronic ground state (hot AC). 1-2% of the AC is generated in the lowest triplet state, but no AC is generated in electronically excited singlet states. Generation and cooling of hot AC are modeled using solution phase and broadened gas-phase AC absorption spectra at various temperatures. Results indicate ultrafast generation of hot AC within 3 ps, much faster than reported before for derivatives of anthracene endoperoxide, and subsequent cooling with an 18 ps time constant. The homolytic O-O cleavage pathway generates a biradical, which converts into electronically excited diepoxide (DE). Our data indicate a 1.5 ps time constant that we tentatively assign to the biradical decay and DE formation. Cooling of DE in this electronically excited state takes place with a ∼21 ps time constant. Excitation of AQ at 266 nm is followed by an ultrafast population of the T(1)(nπ*) triplet state of AQ with a time constant of (160 ± 60) fs.
在飞秒紫外泵浦超连续探针实验中，研究了蒽-9,10-内过氧化物（APO）的双重光化学，同时还比较了蒽（AC）和蒽醌（AQ）。在 282nm 处激发 APO 会通过两种竞争光反应通道导致 100%的产物形成。环重排以约 25%的量子产率（QY）（1）O（2）和在单重电子基态中振动激发的 AC（热 AC）生成。1-2%的 AC 在最低三重态中生成，但在电子激发的单重态中没有 AC 生成。使用溶液相和在不同温度下拓宽的气相 AC 吸收光谱对热 AC 的生成和冷却进行建模。结果表明，热 AC 在 3ps 内超快生成，比以前报道的蒽内过氧化物衍生物快得多，随后以 18ps 的时间常数冷却。均裂 O-O 裂解途径生成双自由基，该双自由基转化为电子激发的双环氧化物（DE）。我们的数据表明 1.5ps 的时间常数，我们暂时将其分配给双自由基衰变和 DE 形成。在这个电子激发态下，DE 的冷却以约 21ps 的时间常数发生。在 266nm 处激发 AQ 后，AQ 的 T（1）（nπ*）三重态以（160±60）fs 的时间常数迅速被占据。
