Kobayashi Yoichi, Fukuda Daiki, Okayasu Yoshinori, Nagai Yuki
Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan.
J Chem Phys. 2024 Jul 21;161(3). doi: 10.1063/5.0205882.
Stepwise two-photon absorption processes have received considerable attention, especially in photocatalysis, due to their relatively lower power threshold, characteristic spatial selectivity, amplification of chemical reactions, and so on. Meanwhile, studies on the relaxation dynamics of higher excited states in condensed systems have been limited for several molecular systems due to the short-lived nature of these states. In this study, we synthesized perylene-substituted perylene bisimide (PBI) and its derivate as model compounds and investigated their excited-state dynamics, including higher excited states, using pump-repump-probe spectroscopy. We revealed that these molecules form charge-transfer (CT) states instantaneously after the excitation, regardless of whether it is the perylene moiety or the PBI moiety that is excited. The lifetime of the CT state was shorter when the distance between the donor (perylene) and the acceptor (PBI) was shorter. Moreover, we also revealed that a higher-lying CT state generated by the stepwise excitation of the CT state using a 740-nm pulse induced Stark effect to the neighboring perylene moiety. The Stark effect not only gives more detailed information about the CT state, but also presents the possibility of new photofunctions, such as instantaneous modulation of the electronic state to achieve optimal electronic properties. These insights contribute to understanding advanced photochemical reactions and would be important for exploring photocatalytic reactions involving higher excited states.
由于其相对较低的功率阈值、独特的空间选择性、化学反应放大等特性，逐步双光子吸收过程受到了广泛关注，尤其是在光催化领域。同时，由于凝聚态系统中较高激发态的寿命较短，对于几种分子系统，关于这些态的弛豫动力学的研究一直有限。在本研究中，我们合成了苝取代的苝双酰亚胺（PBI）及其衍生物作为模型化合物，并使用泵浦-再泵浦-探测光谱研究了它们的激发态动力学，包括较高激发态。我们发现，无论激发的是苝部分还是PBI部分，这些分子在激发后都会立即形成电荷转移（CT）态。当供体（苝）和受体（PBI）之间的距离较短时，CT态的寿命较短。此外，我们还发现，使用740 nm脉冲对CT态进行逐步激发所产生的较高能级CT态会对相邻的苝部分产生斯塔克效应。斯塔克效应不仅能提供有关CT态的更详细信息，还展示了新的光功能的可能性，例如通过瞬时调制电子态来实现最佳电子性质。这些见解有助于理解先进的光化学反应，对于探索涉及较高激发态的光催化反应具有重要意义。
