Ahrens J, Frank M, Clever G H, Schwarzer D
Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
Phys Chem Chem Phys. 2017 May 31;19(21):13596-13603. doi: 10.1039/c7cp02253k.
Photo-induced processes in self-assembled coordination cages were studied by femtosecond infrared pump-probe spectroscopy. Densely packed, interpenetrated double cages were constructed from eight bis-monodentate redoxactive ligands bound to four Pd(ii) nodes. Two types of ligands consisting of electron rich phenothiazine (PTZ) or electron deficient anthraquinone (ANQ) chromophores were used to assemble either homo-octameric or mixed-ligand cages. Upon photoexcitation the homo-octameric acceptor cage undergoes intersystem crossing to a long-lived triplet state, similar to the free acceptor ligand. Excitation of the free donor ligand leads to a fluorescent state with intramolecular charge transfer character. This fluorescence is completely quenched in the homo-octameric donor double cage due to a ligand-to-metal charge transfer followed by back electron transfer on a ps timescale. Only for the mixed-ligand cage irradiation produces a charge separated state with an oxidized PTZ radical cation and a reduced ANQ radical anion as proven by their vibrational fingerprints in the transient IR spectra. In dichloromethane the lifetime of this charge separated state extends from tens of ps to >1.5 ns which is attributed to the broad distribution of mixed-ligand cages with different stoichiometry and/or stereo configurations.
通过飞秒红外泵浦 - 探测光谱研究了自组装配位笼中的光诱导过程。由八个与四个Pd(ii)节点结合的双单齿氧化还原活性配体构建了紧密堆积、相互贯穿的双笼。使用两种由富电子的吩噻嗪（PTZ）或缺电子的蒽醌（ANQ）发色团组成的配体来组装同八聚体或混合配体笼。光激发后，同八聚体受体笼经历系间窜越到长寿命三重态，类似于游离受体配体。游离供体配体的激发导致具有分子内电荷转移特征的荧光态。由于配体到金属的电荷转移，随后在皮秒时间尺度上发生反向电子转移，这种荧光在同八聚体供体双笼中完全猝灭。仅对于混合配体笼，照射产生电荷分离态，其中氧化的PTZ自由基阳离子和还原的ANQ自由基阴离子，这在瞬态红外光谱中通过它们的振动指纹得到证实。在二氯甲烷中，这种电荷分离态的寿命从几十皮秒延长到>1.5纳秒，这归因于具有不同化学计量和/或立体构型的混合配体笼的广泛分布。
