Herz Julia, Buckup Tiago, Paulus Fabian, Engelhart Jens U, Bunz Uwe H F, Motzkus Marcus
†Physikalisch-Chemisches Institut, Im Neuenheimer Feld 229, ‡Organisch-Chemisches Institut, Im Neuenheimer Feld 270, and §Centre of Advanced Materials, Im Neuenheimer Feld 225, Ruprecht-Karls-Universität, Heidelberg D-69120, Germany.
J Phys Chem A. 2015 Jun 25;119(25):6602-10. doi: 10.1021/acs.jpca.5b02212. Epub 2015 Jun 12.
Femtosecond pump-depletion-probe experiments were carried out in order to shed light on the ultrafast excited-state dynamics of triisopropylsilylethynyl (TIPS)-pentacene and two nitrogen-containing derivatives, namely, diaza-TIPS-pentacene and tetraaza-TIPS-pentacene. Measurements performed in the visible and near-infrared spectral range in combination with rate model simulations reveal that singlet fission proceeds via the extremely short-lived intermediate (1)TT state, which absorbs in the near-infrared spectral region only. The T1 → T3 transition probed in the visible region shows a rise time that comprises two components according to a consecutive reaction (S1 → (1)TT → T1). The incorporation of nitrogen atoms into the acene structure leads to shorter dynamics, but the overall triplet formation follows the same kinetic model. This is of particular importance, since experiments on tetraaza-TIPS-pentacene allow for investigation of the triplet state in the visible range without an overlapping singlet contribution. In addition, the pump-depletion-probe experiments show that the triplet absorption in the visible (T1 → T3) and near-infrared (T1 → T2) regions occurs from the same initial state, which was questioned in previous studies. Furthermore, an additional ultrafast transfer between the excited triplet states (T3 → T2) is identified, which is also in agreement with the rate model simulation. By applying depletion pulses, which are resonant with higher vibrational levels, we gain insight into internal vibrational energy redistribution processes within the triplet manifold. This additional information is of great relevance regarding the study of loss channels within these materials.
为了深入了解三异丙基硅乙炔基（TIPS）-并五苯及其两种含氮衍生物（即二氮杂-TIPS-并五苯和四氮杂-TIPS-并五苯）的超快激发态动力学，进行了飞秒泵浦-耗尽-探测实验。在可见和近红外光谱范围内进行的测量结合速率模型模拟表明，单线态裂变通过寿命极短的中间体（1）TT态进行，该态仅在近红外光谱区域吸收。在可见光区域探测到的T1→T3跃迁显示出一个上升时间，根据连续反应（S1→（1）TT→T1），该上升时间包含两个分量。在并苯结构中引入氮原子会导致动力学过程缩短，但总的三线态形成遵循相同的动力学模型。这一点尤为重要，因为对四氮杂-TIPS-并五苯的实验允许在无重叠单线态贡献的情况下在可见光范围内研究三线态。此外，泵浦-耗尽-探测实验表明，可见光（T1→T3）和近红外（T1→T2）区域的三线态吸收来自相同的初始态，这在先前的研究中存在疑问。此外，还确定了激发三线态之间的额外超快转移（T3→T2），这也与速率模型模拟一致。通过应用与更高振动能级共振的耗尽脉冲，我们深入了解了三线态多重态内的内部振动能量重新分布过程。这些额外信息对于研究这些材料中的损耗通道具有重要意义。
