Ground-and Excited-State Characterization of an Electrostatic Complex between Tetrakis-(4-Sulfonatophenyl)porphyrin and 16-Pyrimidinium Crown-4 |
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Authors: | Randy W Larsen Michael K Helms W Russell Everett David M Jameson |
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Institution: | Departments of Chemistry, University of Hawaii at Manoa, Honolulu, HI, USA;Genetics and Molecular Biology, University of Hawaii at Manoa, Honolulu, HI, USA |
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Abstract: | Abstract— We report the formation of an electrostatic complex between (16-pyrimidinium crown-4)tetranitrate (16PC4) and tetrakis-(4-sulfonatophenyl)porphyrin (4SP) in aqueous solution. Ground-state complex formation results in a red shift of the 4SP visible absorption bands and a decrease in absorbance of the Soret band. The equilibrium constant for complex formation (determined from optical titrations) is found to be (2.0 ± 0.2) × 105 M ?1. In addition, the data fit to an expression describing a 1:1 stoichiometry. Excitation of the complex results in quenching of both the excited singlet and triplet states of the associated porphyrin. The singlet-state lifetime decreases from 10 ns for the free porphyrin to 1.5 ns in the presence of 16PC4 at low solution ionic strengths. In addition, evidence is presented for triplet-state quenching within the complex with k q= (1.1 ± 0.1) × 104 s?1. The mechanism of quenching is tentatively assigned to electron transfer from either the excited singlet or excited triplet state of the porphyrin to the ground state of the 16PC4. |
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