Electron paramagnetic resonance and optical evidence for two distinct porphyrin triplet states in linked porphyrin-quinone molecules
The authors have carried out a spectroscopic and photophysical study of the triplet states of a series of meso-tetratolylporphyrins to which certain molecular moieties have been covalently attached via diamide linkages, the two amides being separated by n methylene groups (n = 2-4). The attached end groups include methyl-p-benzoquinone, the corresponding hydroquinone, and dimethoxybenzene. At low temperatures (approx.90 K) in frozen solvent matrices, the authors have found electron paramagnetic resonance (EPR) spectral evidence of two triplet states with different zero-field splitting parameters. The authors attribute this behavior to conformational heterogeneity in the linked molecules. The data are best interpreted as arising from perturbed (i.e., complexed) or normal (i.e., extended) porphyrin triplets. This is consistent with the previous interpretations of the absorption and fluorescence properties of these molecules. The EPR intensities also exhibit spectra photoselection on excitation in red-shifted and broadened porphyrin Soret band. Over the temperature range 80-300 K, laser flash photolysis experiments with time resolved detection of optical absorption show decay kinetics for these same linked porphyrin molecules which confirm the existence of two porphyrin triplets with different lifetimes in the complexed and extended conformers, respectively. Kinetic analysis of the transient absorbance profiles suggest that interconversion of the two molecular forms is slow on the time scale of a few hundred microseconds, even at room temperature.
- Research Organization:
- Univ. of Western Ontario, London
- OSTI ID:
- 7005524
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 90:22
- Country of Publication:
- United States
- Language:
- English
Similar Records
Influence of linking alkyl chain length on photoinduced intramolecular electron transfer in bipyridine-linked porphyrin-RuO sub 2 clusters
Syntheses of covalently-linked porphyria-quinone complexes. I
Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
PORPHYRINS
ABSORPTION SPECTROSCOPY
ELECTRON SPIN RESONANCE
PHOTOLYSIS
QUINONES
CHEMICAL REACTION KINETICS
EXPERIMENTAL DATA
LOW TEMPERATURE
MEDIUM TEMPERATURE
P STATES
AROMATICS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
DATA
DECOMPOSITION
ENERGY LEVELS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
MAGNETIC RESONANCE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
REACTION KINETICS
RESONANCE
SPECTROSCOPY
400500* - Photochemistry