Untersuchung der selbst‐sensibilisierten Photooxidation des Rubrens in verschiedenen Lösungsmitteln

Abstract

Die Gesamtquantenausbeute der selbst‐sensibilisierten Photooxidation des Rubrens wurde in Benzol, Toluol, Chloroform, 1,2,4‐Trichlor‐benzol, Tetrachlorkohlenst off und Schwefelkohlenstoff in Abhängigkeit von der Sauerstoffkonzentration und der Rubrenkonzentration bei 25 ± 2°C gemessen. Weiterhin wurden die relativen Fluoreszenzquantenausbeuten, die Fluoreszenzabklingdauern und die Konstanten für die Sauerstofflöschung der Fluoreszenz ermittelt. Die Analyse der kinetischen Daten steht mit der Annahme im Einklang, daß Singulettsauerstoff sowohl durch Rubrenmoleküle im ersten angeregten Singulettzustand als auch durch Rubrenmoleküle im niedrigsten Triplettzustand erzeugt wird. Es wird gezeigt, daß die Abhängigkeit der Photooxidation des Rubrens vom Lösungsmittel vornehmlich durch die unterschiedlichen Lebensdauern des Singulettsauerstoffs in verschiedener Umgebung bedingt wird.

Physical Mechanisms of Generation and Deactivation of Singlet Oxygen

“…Figure shows the excellent linear plot obtained with the CHCl 3 data, with the intercept for = 2 at 1 − ( F / F 0 ) = 1. Thus, Brauer and Wagner first demonstrated that both the T 1 state and O 2 ( 1 Δ g ) may be formed during the fluorescence quenching by O 2 and that the maximum value of Q Δ is 2 . This important result was confirmed by both authors in the subsequent investigation of the self-sensitized photo-oxygenation of heterocoerdianthrone .…”

“…Division by the corresponding reaction efficiencies f R yielded values of + S Δ = 1.6 (toluene), 1.7 (benzene), 2.1 (CHCl 3 ), 1.7 (C 6 H 3 Cl 3 ), 1.9 (CCl 4 ), and 2.1 (CS 2 ). Since , , and S Δ cannot be larger than 1, this result clearly indicates that, for rubrene, both processes 52 and 58 contribute to O 2 ( 1 Δ g ) formation, with efficiencies near or equal to unity …”

“…With the exception of a few compounds with high oxidation potentials and low excited-state energies, the experimental overall S 1 quenching rate constants are found to be nearly collision-controlled in the gas phase ,,, or diffusion-controlled in the liquid phase. ,,,− However, all quenching pathways compete with relatively efficient intramolecular deactivation processes, and values distinctly smaller than unity are commonly found under air-saturated conditions in solution. The first experimental studies were concerned with the multiplicity of the sensitizer product state, and it was shown that isc (eqs 50−53) is dominant over ic (eqs 54−56); i.e., oxygen quenching of S 1 states leads mainly to formation of a triplet state. ,− Brauer and Wagener , first provided clear evidence for overall singlet oxygen yields larger than unity, thus showing that the energy-transfer process 52 can significantly contribute to the deactivation of S 1 . These observations are obviously limited to molecules having a S 1 −T 1 energy gap larger than 94 kJ mol -1 , such as rubrene, ,,− heterocoerdianthrone, , tetracene, ,,, perylene, ,,, pyrene, ,,− chrysene, ,− 1,3-diphenylisobenzofuran, 1,6-diphenylhexatriene, fluoranthene, , a larg...…”

“…The first experimental studies were concerned with the multiplicity of the sensitizer product state, and it was shown that isc (eqs 50−53) is dominant over ic (eqs 54−56); i.e., oxygen quenching of S 1 states leads mainly to formation of a triplet state. ,− Brauer and Wagener , first provided clear evidence for overall singlet oxygen yields larger than unity, thus showing that the energy-transfer process 52 can significantly contribute to the deactivation of S 1 . These observations are obviously limited to molecules having a S 1 −T 1 energy gap larger than 94 kJ mol -1 , such as rubrene, ,,− heterocoerdianthrone, , tetracene, ,,, perylene, ,,, pyrene, ,,− chrysene, ,− 1,3-diphenylisobenzofuran, 1,6-diphenylhexatriene, fluoranthene, , a large series of anthracene derivatives, ,,,,− and several organic cations . No evidence has been obtained for process 50.…”

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35 Dependence of Q Δ on 1 − ( F / F 0 ) for the sensitization of O 2 ( 1 Δ g ) by rubrene in CHCl 3 . Reprinted with permission from ref . Copyright 1975 Deutsche Bunsen-Gesellschaft.

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