Electron paramagnetic resonance and optical evidence for two distinct porphyrin triplet states in linked porphyrin-quinone molecules

Journal Article · Thu Oct 23 04:00:00 EDT 1986 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100280a032· OSTI ID:7005524

McIntosh, A R; Bolton, J R; Connolly, J S; Marsh, K L; Cook, D R; Ho, T F; Weedon, A C

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), Journal Name: J. Phys. Chem.; (United States) Vol. 90:22; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ABSORPTION SPECTROSCOPY
AROMATICS
CARBOXYLIC ACIDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
DECOMPOSITION
ELECTRON SPIN RESONANCE
ENERGY LEVELS
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
LOW TEMPERATURE
MAGNETIC RESONANCE
MEDIUM TEMPERATURE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
P STATES
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PORPHYRINS
QUINONES
REACTION KINETICS
RESONANCE
SPECTROSCOPY