Triplet-state formation of porphycenes. Intersystem crossing versus sensitization mechanisms

Journal Article · Thu May 05 04:00:00 EDT 1988 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100320a009· OSTI ID:7143514

Levanon, H; Toporowicz, M; Ofir, H; Fessenden, R W; Das, P K; Vogel, E; Koecher, M; Pramod, K

The authors report on a study of the photoexcited triplet state, in the liquid phase, of the following free-base porphycenes: parent porphycene (H/sub 2/PCl), 2,7,12,17-tetra-n-propylporphycene (H/sub 2/PC2), and 9,10,19,20-tetra-n-propylporphycene (H/sub 2/PC3). The triplet states are produced by two independent experimental methods: (i) singlet-triplet intersystem crossing following laser excitation; (ii) triplet-triplet sensitization, following pulse radiolysis of the same solutions as in (i) and the sensitizer, ..beta..-acetonaphthone. The latter method produces comparable yields of the photoexcited triplet, at room temperature, independent of the substitution site, whereas in the former method, the triplet yield of H/sub 2/PC3 is negligible at room temperature. The triplet-triplet absorption of the alkyl-substituted free-base porphycene, H/sub 2/PC3/sup T/, starts to show a reasonable signal-to-noise ratio only at temperatures below approx. 240 K. This temperature dependence is interpreted in terms of a thermally activated excited state in the singlet manifold, approx. 1000 cm/sup -1/ above S/sub 1/. Supporting evidence for such a mechanism is provided by the similarity of the temperature dependence of the triplet-triplet absorption and fluorescence intensity of H/sub 2/PC3.

• Research Organization: Univ. of Notre Dame, IN (USA)
• OSTI ID: 7143514
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:9; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400500* -- Photochemistry
400600 -- Radiation Chemistry
ABSORPTION SPECTROSCOPY
CARBOXYLIC ACIDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
DATA
DECOMPOSITION
ENERGY TRANSFER
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
MEDIUM TEMPERATURE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PORPHYRINS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIOLYSIS
SPECTROSCOPY
TEMPERATURE DEPENDENCE