Tannert Sebastian, Ermilov Eugeny A, Vogel Jörn Oliver, Choi Michael T M, Ng Dennis K P, Röder Beate
Institut für Physik, Photobiophysik, Humboldt Universität Berlin, Newtonstrasse 15, D-12489 Berlin, Germany.
J Phys Chem B. 2007 Jul 19;111(28):8053-62. doi: 10.1021/jp0724222. Epub 2007 Jun 21.
Heteroporphyrin and -phthalocyanine arrays represent an attractive class of light harvesters and charge-separation systems exhibiting an easy route of synthesis and high chemical stability. In the present work, we report the results of photophysical investigations of two novel non-sandwich-type porphyrin-phthalocyanine heterotriads, in which two meso-tetraphenylporphyrin rings (H2TPP or ZnTPP) are linked to the central silicon atom of a silicon(IV) phthalocyanine core. It was found that the photophysical properties of the triads (H2Tr and ZnTr) in N,N-dimethylformamide (DMF) and toluene are strongly affected by two different types of interaction between the porphyrin (P) and the phthalocyanine (Pc) parts, namely excitation energy transfer (EET) and photoinduced charge transfer. The first process results in appearance of the Pc fluorescence when the P-part is initially excited, and plays a dominant role in fast depopulation of the first excited singlet state of the P moiety. If the first excited singlet state of the Pc-part is populated (either directly or via EET), it undergoes fast depopulation by hole transfer (HT) to the charge-separated (CS) state. In polar DMF, the CS state is the lowest excited state, and the charge recombination occurs directly to the ground state. Using transient absorption spectroscopy, the lifetime of the CS state was estimated to be 30 and 20 ps for H2Tr and ZnTr, respectively. In nonpolar toluene, the energy gap between the first excited singlet state of the Pc-part and the CS state is very small, and back HT occurs in both triads, resulting in appearance of "delayed fluorescence" of the Pc-part with a decay time similar to the lifetime of the CS state (190 and 280 ps for H2Tr and ZnTr, respectively). Since the energy of the CS state of ZnTr in toluene is lower than that of H2Tr, the probability of back HT for ZnTr is lower. This was clearly proved by decay-associated fluorescence spectral measurements.
杂卟啉和酞菁阵列是一类引人注目的光捕获器和电荷分离系统，具有合成路线简便和化学稳定性高的特点。在本工作中，我们报道了两种新型非夹心型卟啉 - 酞菁异质三联体的光物理研究结果，其中两个中位 - 四苯基卟啉环（H2TPP或ZnTPP）与硅（IV）酞菁核的中心硅原子相连。研究发现，在N，N - 二甲基甲酰胺（DMF）和甲苯中，三联体（H2Tr和ZnTr）的光物理性质受到卟啉（P）和酞菁（Pc）部分之间两种不同类型相互作用的强烈影响，即激发能量转移（EET）和光诱导电荷转移。第一个过程导致当P部分最初被激发时出现Pc荧光，并且在P部分的第一激发单重态的快速去激发中起主导作用。如果Pc部分的第一激发单重态被填充（直接或通过EET），它会通过空穴转移（HT）快速去激发到电荷分离（CS）态。在极性DMF中，CS态是最低激发态，电荷复合直接发生到基态。使用瞬态吸收光谱法，估计H2Tr和ZnTr的CS态寿命分别为30和20 ps。在非极性甲苯中，Pc部分的第一激发单重态与CS态之间的能隙非常小，并且在两个三联体中都发生反向HT，导致Pc部分出现“延迟荧光”，其衰减时间类似于CS态的寿命（H2Tr和ZnTr分别为190和280 ps）。由于甲苯中ZnTr的CS态能量低于H2Tr，ZnTr的反向HT概率较低。这通过与衰减相关的荧光光谱测量得到了明确证明。
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