Relaxation dynamics of photoexcited resorcinol: internal conversion versus H atom tunnelling.
Relaxation dynamics of photoexcited resorcinol: internal conversion versus H atom tunnelling.
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DOI：
10.1039/c3cp53726a
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发表时间：
2014-01
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通讯作者：
J. D. Young;M. Staniforth;A. Chatterley;M. Paterson;G. Roberts;V. Stavros
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作者：
J. D. Young;M. Staniforth;A. Chatterley;M. Paterson;G. Roberts;V. Stavros
用时间分辨速度图离子成像和超快时间分辨离子产额测量结合互补从头计算，研究了间苯二酚(1，3-二苯酚)在278≥λ≥255 nm泵浦波长范围内的激发态动力学。在激发到1(1)ππ*态后，我们提取了激发态弛豫的时间标度τ1，它随激发能量从2.7 ns减小到~120ps。这被分配给相互竞争的放松机制。在1(1)ππ*/(1)πσ*锥形交点下方隧穿，然后耦合到解离的(1)πσ*态，产生具有高动能(~5,000 cm(-1))的H原子。这种机制与能够将布居从光激发的1(1)ππ*态转移回振动激发的基态S0*的内部转换过程相竞争。当激发波长在2 6 4-2 6 0 nm之间时，观察到第二个衰变分量τ2，我们对τ2的起源提出了几种可能的解释，包括构象特有的动力学。用237nm光激发(在1(1)ππ*/(1)πσ*锥形交点以上)产生高动能氢原子(~11,000 cm(-1))，产生~260fs，符合1(1)ππ*(或2(1)ππ*)和(1)πσ*态之间的超快耦合然后解离的机制。这些结果突出了额外官能团的存在，更具体地说，官能团的精确位置，可以对紫外光激发后模型杂芳烃体系的激发态动力学产生深远的影响。
The excited state dynamics of resorcinol (1,3-dihydroxybenzene) following UV excitation at a range of pump wavelengths, 278 ≥ λ ≥ 255 nm, have been investigated using a combination of time-resolved velocity map ion imaging and ultrafast time-resolved ion yield measurements coupled with complementary ab initio calculations. After excitation to the 1(1)ππ* state we extract a timescale, τ1, for excited state relaxation that decreases as a function of excitation energy from 2.70 ns to ~120 ps. This is assigned to competing relaxation mechanisms. Tunnelling beneath the 1(1)ππ*/(1)πσ* conical intersection, followed by coupling onto the dissociative (1)πσ* state, yields H atoms born with high kinetic energy (~5000 cm(-1)). This mechanism is in competition with an internal conversion process that is able to transfer population from the photoexcited 1(1)ππ* state back to a vibrationally excited ground state, S0*. When exciting between 264-260 nm a second decay component, τ2, is observed and we put forth several possible explanations as to the origins of τ2, including conformer specific dynamics. Excitation with 237 nm light (above the 1(1)ππ*/(1)πσ* conical intersection) yields high kinetic energy H atoms (~11,000 cm(-1)) produced in ~260 fs, in line with a mechanism involving ultrafast coupling between the 1(1)ππ* (or 2(1)ππ*) and (1)πσ* state followed by dissociation. The results presented highlight the profound effect the presence of additional functional groups, and more specifically the precise location of the functional groups, can have on the excited state dynamics of model heteroaromatic systems following UV excitation.