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Issue 11, 2010
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Ultrafast intramolecular charge transfer in tetrapyrazinoporphyrazines controls the quantum yields of fluorescence and singlet oxygen

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Abstract

A series of octasubstituted zinc(II) tetrapyrazinoporphyrazines (TPyzPz), aza-analogues of phthalocyanines, differing in the number of peripheral N,N-diethylamino (n = 0–8) and tert-butylsulfanyl substituents (m = 8 − n) has been synthesized. All possible congeners were characterized including adjacent and opposite isomers. Steady-state (UV-vis, fluorescence) and time-resolved (fluorescence, femtosecond transient absorption) spectroscopies, redox and photochemical (singlet oxygen formation) properties were investigated and compared. The peripheral tertiary amino substituents (donor) induce a new competitive relaxation pathway to fluorescence and intersystem crossing due to the mixing of the first excited state S1 of the TPyzPz macrocycle with a nearby intramolecular charge transfer (ICT) state. The fluorescence quantum yield and fluorescence lifetime of 6Zn bearing one N,N-diethylamino substituent (n = 1, m = 7) decreased with increasing solvent polarity, while the same observables of 5Zn with no donor centre (n = 0, m = 8) were not affected. Protonation of the N,N-diethylamino substituent in 6Zn led to a strong increase of the fluorescence intensity. The cyclic voltammetry data, the steady-state and time-resolved emission and transient absorption studies revealed strong electronic coupling between the TPyzPz moiety and N,N-diethylamino substituents. ICT is an extremely rapid process occurring with a time constant of 10 ps and 7 ps in 6Zn (n = 1, m = 7) and 11Zn (n = 8, m = 0) in pyridine, respectively. The ICT efficiency decreased in non-polar solvents. The presence of two N,N-diethylamino substituents in 7Zn (n = 2, m = 6) considerably quenched the S1 states in pyridine (polar, coordinating), toluene (non-polar, non-coordinating) and toluene–1% pyridine (v/v) (non-polar, coordinating). The photophysical properties of compounds with more donor substituents on the periphery (n > 2, m < 6) were similar to those of 7Zn.

Graphical abstract: Ultrafast intramolecular charge transfer in tetrapyrazinoporphyrazines controls the quantum yields of fluorescence and singlet oxygen

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Publication details

The article was received on 09 Sep 2009, accepted on 18 Nov 2009 and first published on 21 Jan 2010


Article type: Paper
DOI: 10.1039/B918546A
Citation: Phys. Chem. Chem. Phys., 2010,12, 2555-2563
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    Ultrafast intramolecular charge transfer in tetrapyrazinoporphyrazines controls the quantum yields of fluorescence and singlet oxygen

    V. Novakova, P. Zimcik, M. Miletin, L. Vachova, K. Kopecky, K. Lang, P. Chábera and T. Polívka, Phys. Chem. Chem. Phys., 2010, 12, 2555
    DOI: 10.1039/B918546A

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