Murdock Daniel, Ingle Rebecca A, Sazanovich Igor V, Clark Ian P, Harabuchi Yu, Taketsugu Tetsuya, Maeda Satoshi, Orr-Ewing Andrew J, Ashfold Michael N R
School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Central Laser Facility, Research Complex at Harwell, Science and Technologies Facilities Council, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, UK.
Phys Chem Chem Phys. 2016 Jan 28;18(4):2629-38. doi: 10.1039/c5cp06597f.
The photoisomerisation dynamics following excitation to the S1 electronic state of two structurally related heterocyclic molecules, α-pyrone and coumarin, in acetonitrile solution have been probed by time-resolved vibrational absorption spectroscopy. Following irradiation at 310 nm, α-pyrone relaxes rapidly from its initially excited state, with a quantum yield for parent molecule reformation of 68%. Probing the antisymmetric ketene stretch region between 2100 cm(-1) and 2150 cm(-1) confirms the presence of at least two isomeric ring-opened photoproducts, which are formed highly vibrationally excited and relax on a picosecond timescale. Following vibrational cooling, a secondary, thermally driven, isomerisation is observed with a 1.8(1) ns time constant. In contrast, coumarin reforms the parent molecule with essentially 100% efficiency following excitation at 330 nm. The conical intersections driving the non-radiative relaxation of α-pyrone have been investigated using an automated search algorithm. The two lowest energy conical intersections possess remarkably similar structures to the two energetically accessible conical intersections reported previously for coumarin, suggesting that the differing photochemistry is the result of dynamical effects occurring after passage through these intersections.
通过时间分辨振动吸收光谱法，研究了乙腈溶液中两种结构相关的杂环分子α-吡喃酮和香豆素激发到S1电子态后的光异构化动力学。在310nm处照射后，α-吡喃酮从其初始激发态迅速弛豫，母体分子重新形成的量子产率为68%。探测2100cm(-1)至2150cm(-1)之间的反对称乙烯酮伸缩区域，证实至少存在两种开环光产物异构体，它们以高振动激发态形成，并在皮秒时间尺度上弛豫。振动冷却后，观察到一个二级热驱动异构化过程，时间常数为1.8(1)ns。相比之下，香豆素在330nm激发后，母体分子的重新形成效率基本为100%。使用自动搜索算法研究了驱动α-吡喃酮非辐射弛豫的锥形交叉点。两个最低能量的锥形交叉点与先前报道的香豆素的两个能量可及的锥形交叉点具有非常相似的结构，这表明不同的光化学是通过这些交叉点后发生的动力学效应的结果。
