University of Helsinki, Department of Chemistry, P.O. Box 55 (A.I. Virtanens plats 1), FIN-00014 University of Helsinki, Finland.
Kazan Federal University, Republic of Tatarstan, Russia.
Phys Chem Chem Phys. 2023 Feb 22;25(8):6406-6415. doi: 10.1039/d2cp05275j.
A novel method for calculating rate constants for internal conversion () that simultaneously accounts for Duschinsky, anharmonic and Herzberg-Teller effects has been developed and implemented. This method has been applied to robust planar molecules like tetraoxa[8]circulene (4B), free-base porphyrin (H2P) and pyrometene (PM567) with small Duschinsky rotation ( with almost identical normal coordinates in the ground and excited states) and to poly[]fluorenes (P[n]F) ( = 2-14) with a substantial Duschinsky rotation. The obtained results show that the Duschinsky effect is large in the harmonic approximation, whereas it is in general much smaller in the anharmonic approximation. The Duschinsky effect is found to be large for high frequency vibrational modes with energies of ∼3300 cm such as the X-H (X = C, N and O) stretching modes that mix in the S → S electronic transition. However, even in this case, the increase in due to the Duschinsky effect does not exceed one order of magnitude. The calculations show that anharmonic contributions to are larger than Herzberg-Teller contributions which in turn are larger than contributions from the Duschinsky effect ANH > HT > Du. We also show that an approximation, where only X-H bonds are considered in the calculation, is accurate even for P[n]F ( = 2-14).
一种新的计算内转换速率常数（）的方法已经被开发出来并实施，该方法同时考虑了杜兴斯基、非谐和和赫茨伯格-泰勒效应。该方法已应用于坚固的平面分子，如四氧杂[8]轮烯（4B）、自由碱基卟啉（H2P）和吡咯美登（PM567），这些分子的杜兴斯基旋转较小（在基态和激发态下几乎具有相同的正则坐标），以及多[芴]（P[n]F）（= 2-14），这些分子的杜兴斯基旋转较大。得到的结果表明，在简谐近似中杜兴斯基效应较大，而在非谐近似中通常较小。发现杜兴斯基效应在能量约为 3300 cm 的高频振动模式中较大，例如在 S → S 电子跃迁中混合的 X-H（X = C、N 和 O）伸缩模式。然而，即使在这种情况下，由于杜兴斯基效应引起的增加也不超过一个数量级。计算表明，非谐贡献对的贡献大于赫茨伯格-泰勒贡献，而赫茨伯格-泰勒贡献又大于杜兴斯基效应的贡献 ANH > HT > Du。我们还表明，在计算中仅考虑 X-H 键的近似方法即使对于 P[n]F（= 2-14）也是准确的。
