Dithizone, with its derivatives and complexes, is characterized by seven classes of chromic reactions, which make it a remarkable candidate for diverse sensor applications. We now present dithizone’s chromic response to experimental photoexcitation as studied by ultrafast laser spectroscopy, density functional theory (DFT), and complete active space self-consistent field (CASSCF) calculations. After vertical excitation to the first excited state, within 240 fs the reaction proceeds towards an intersystem crossing (ISC) that is coupled with a conical intercept (CI), while the second path proceeds via a second CI. The ISC leads to excited state tautomerization within 1.6 ps to form a triplet excited state product that takes a longer time to return back to reactant ($\sim{5}\;{\rm ns}$), while the first and second CIs both lead to the ground state within 1.6 ps and 12 ps, respectively. Additionally, dynamics through both CIs allow for efficient repopulation of the reactant ground state. Theoretical calculations using minimum energy path analysis and CASSCF calculation (including n-electron valence state perturbation theory multireference perturbation theory correction) gave additional insight into ground and excited state conformational changes that are observed by means of experimental femtosecond laser pulse excitations of dithizone.

中文翻译：

---

通过瞬态吸收光谱和计算机CASSCF研究探索光激发双硫zone的超快反应机理

双硫zone及其衍生物和络合物的特征是七类铬反应，这使其成为各种传感器应用的杰出候选者。现在，我们通过超快速激光光谱，密度泛函理论（DFT）和完整的活性空间自洽场（CASSCF）计算研究了双硫zone对实验光激发的铬响应。在垂直激发到第一激发态之后，在240 fs内，反应进行至系统间交叉（ISC），该系统与圆锥形截距（CI）耦合，而第二路径通过第二CI进行。ISC导致激发态互变异构在1.6 ps内，从而形成三重激发态产物，需要更长的时间才能返回到反应物（$ \ sim {5} \; {\ rm ns} $），而第一和第二CI分别导致在1.6 ps和12 ps内的基态。另外，通过两个CI的动力学特性可以有效地重新填充反应物基态。使用最小能量路径分析和CASSCF计算的理论计算（包括n电子价态微扰理论，多参考微扰理论校正）提供了对双硫zone飞秒激光脉冲激发实验观察到的基态和激发态构象变化的进一步了解。