The Influence of Solvent Polarity and Metalation on Energy and Electron Transfer in Porphyrin-Phthalocyanine Heterotrimers

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• 作者：Sebastian Tannert ; Eugeny A. Ermilov ; J&ouml ; rn Oliver Vogel ; Michael T. M. Choi ; Dennis K. P. Ng ; Beate R&ouml ; der
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：July 19, 2007
• 年：2007
• 卷：111
• 期：28
• 页码：8053 - 8062
• 全文大小：375K
• 年卷期：v.111,no.28(July 19, 2007)
• ISSN：1520-5207

文摘

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, wereport the results of photophysical investigations of two novel non-sandwich-type porphyrin-phthalocyanineheterotriads, in which two meso-tetraphenylporphyrin rings (H₂TPP or ZnTPP) are linked to the central siliconatom of a silicon(IV) phthalocyanine core. It was found that the photophysical properties of the triads (H₂Trand ZnTr) in N,N-dimethylformamide (DMF) and toluene are strongly affected by two different types ofinteraction 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 whenthe P-part is initially excited, and plays a dominant role in fast depopulation of the first excited singlet stateof the P moiety. If the first excited singlet state of the Pc-part is populated (either directly or via EET), itundergoes fast depopulation by hole transfer (HT) to the charge-separated (CS) state. In polar DMF, the CSstate is the lowest excited state, and the charge recombination occurs directly to the ground state. Usingtransient absorption spectroscopy, the lifetime of the CS state was estimated to be 30 and 20 ps for H₂Tr andZnTr, respectively. In nonpolar toluene, the energy gap between the first excited singlet state of the Pc-partand the CS state is very small, and back HT occurs in both triads, resulting in appearance of "delayedfluorescence" of the Pc-part with a decay time similar to the lifetime of the CS state (190 and 280 ps forH₂Tr 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 fluorescencespectral measurements.