Dynamics of the cycloreversion reaction of a photochromic diarylethene derivative with a small ring-opening reaction yield (∼1%) was investigated by using femtosecond transient absorption spectroscopy. The reaction rate constant and activation barrier on the reaction coordinate were quantitatively analyzed on the basis of the temperature and excitation wavelength dependencies of the reaction yield and excited state dynamics. From the comparison of the present results with those in a more reactive derivative, we concluded that a key factor regulating the overall reaction yield is the branching ratio at the conical intersection where the excited state population is split into the product and the initial reactant. The excitation wavelength dependence of the dynamics indicated that the geometrical relaxation and vibrational cooling proceed in a few picosecond time scale behind the cycloreversion process, and the vibrational excess energy assists the molecule to climb up the energy barrier.

中文翻译：

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飞秒时间分辨吸收光谱法揭示了二芳基乙烯衍生物的环还原反应性的主要因素。

通过飞秒瞬态吸收光谱研究了光致变色二芳基乙烯衍生物的环还原反应动力学，该反应的开环反应收率较低（〜1％）。根据反应收率和激发态动力学对温度和激发波长的依赖性，定量分析了反应速率常数和反应坐标上的活化势垒。通过将本结果与反应性更高的衍生物的结果进行比较，我们得出结论，调节总体反应收率的关键因素是在圆锥形交叉点处的分支比，在该圆锥形交叉点处，激发态种群被分为产物和初始反应物。