Water-soluble porphyrin monomer—dimer systems: fluorescence dynamics and thermodynamic properties
✍ Scribed by Klaus Kemnitz; Toru Sakaguchi
- Publisher
- Elsevier Science
- Year
- 1992
- Tongue
- English
- Weight
- 584 KB
- Volume
- 196
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
Fluorescent dimers allow the direct determination of their thermodynamic properties from kinetic analysis of the temperaturedependent two-exponential fluorescence decay of the monomer-dimer system. Monomers and dimers of tetra(carboxyphenyl)porphine in water at pH= 8 have lifetimes of 8.9 f 0.2 and 5.1* 0.5 ns, respectively, at 23°C. In contrast, the monomer lifetime for tetra(N-methylpyridyl)porphine in water is 1.3 f 0.2 ns and much shorter than for the dimer, which is 4.9 + 0.4 ns. Global analysis yields temperature-dependent preexponential factors from which dimer equilibrium constants, and enthalpies and entropies of dimerization can be derived. We obtained A&= -5000 cm-' and A&= -8.7 cm-i K-i for the tetranegative porphyrin, but A&= + 1150 cm-' and A&= + 13.4 cm-' K-' for the tetrapositive derivative, where dimerization seems to be entropy driven.