In this computational study we explore the photodynamics of malonaldehyde and compare it to that of the homologous acetylacetone. Upon photoexcitation to the bright $S_2(\pi {\pi }^{\ast })$ state malonaldehyde relaxes to the $S_1(n{\pi }^{\ast })$ state on an ultrashort time scale. Once in the $S_1(n{\pi }^{\ast })$ state the population of malonaldehyde splits. Part of the population undergoes internal conversion to the ground state by deplanarization of the H-chelate ring, while the other part crosses to the triplet manifold. The comparison with acetylacetone reveals a substantial increase of the internal conversion pathways, from less than 20% in acetylacetone to 40% in malonaldehyde. We show that the substitution of the aliphatic hydrogens by the methyl groups reduces the accessibility of the S₁/S₀ conical intersection seam in acetylacetone. The system then crosses to the triplet manifold and homolytic C–CH₃ bond cleavage takes place.

在这项计算研究中，我们探索了丙二醛的光动力学并将其与同源乙酰丙酮的光动力学进行了比较。在光激发下变亮${\mathrm{小号}}_{\mathrm{2个}}（\pi {\pi }^{\ast }）$ 丙二醛向 ${\mathrm{小号}}_{\mathrm{1个}}（ñ{\pi }^{\ast }）$状态在超短时间尺度上。一旦进入${\mathrm{小号}}_{\mathrm{1个}}（ñ{\pi }^{\ast }）$陈述丙二醛分裂的人口。一部分人口通过H螯合物环的去平面化而内部转化为基态，而另一部分则穿过三重态歧管。与乙酰丙酮的比较揭示了内部转化途径的显着增加，从乙酰丙酮的不足20％到丙二醛的40％。我们表明，甲基取代脂肪族氢会降低乙酰丙酮中S ₁ / S ₀圆锥形相交接缝的可及性。然后，系统穿过三重态歧管，并发生均相C–CH ₃键裂解。