Photochemistry of aromatic compounds. Part 5.—Measurement of quantum yields of triplet state formation by flash photolysis

Quantum yields of triplet state formation and extinction coefficients of the triplet states have been determined by direct depletion methods for solutions of anthracene, phenanthrene, 1,2,5,6-dibenzanthracene, fluorescein, dibromofluorescein, eosin and erythrosin. The values obtained for the hydrocarbons are in reasonable agreement with those obtained by other workers using energy transfer and heavy atom perturbation techniques. In all cases which we have studied, the sum of the quantum yields of fluorescence and triplet state formation is equal to unity within the limits of experimental error, showing that radiationless transfer from the excited singlet to the ground state is negligible.

Download Full-text

Singlet Mechanism for Trans → Cis Photoisomerization of Quaternary Salts of 4-Substituted 4′-Azastilbenes (R = CN, H, CH3, and OCH3) and their Quinolinium Analogues. VIII

Zeitschrift für Naturforschung A ◽

10.1515/zna-1985-0520 ◽

1985 ◽

Vol 40 (5) ◽

pp. 525-537 ◽

Cited By ~ 1

Author(s):

H. Görner ◽

A. Fojtik ◽

J. Wróblewski ◽

L. J. Currell

Keyword(s):

Triplet State ◽

Low Temperatures ◽

Room Temperature ◽

Flash Photolysis ◽

Laser Flash Photolysis ◽

Ion Pairs ◽

Laser Flash ◽

Quantum Yields ◽

Polar Solvents ◽

Effects Of Temperature

The trans → cis photoisomerization of a series of substituted stilbazolium salts (At+X− , At+: trans-1-alkyl-4-[4-R-styryl]-pyridinium and -quinolinium, R = CN. H, CH3 and OCH3, X− = I and ClO4−) was studied by laser flash photolysis and steady state irradiation measurements. The quantum yields of cis ⇄ trans photoisomerization (ϕc → t and ϕt → c ) and of fluorescence of the trans isomers (ϕf) were determined in several solvents at room temperature and at low temperatures in mixtures of either 2-methyltetrahydrofuran-dichloromethane or ethanolmethanol (E-M). In polar solvents at room temperature ϕt → c is substantial ( ≧ 0.3) and ϕf is small (10−3-10−2). Competition of fluorescence and an activated step in the trans → cis pathway is indicated by the effects of temperature on ϕf and ϕt → c (activation energy: 2 - 3 kcal/mol). A transient, observed only at low temperatures (lifetime τT > 0.5 ms in E-M below -170°C), is assigned to the lowest triplet state with trans configuration. On the basis of the effects of temperature on ϕf, ϕt → c , and the triplet yield and those of quenchers on ϕf and ϕt → c , involvement of the triplet state in the twisting process at room temperature is excluded. Therefore, a singlet mechanism is suggested for the trans → cis photoisomerization of the stilbazolium salts examined. Significant reduction of ϕt → c for iodides in solvents of moderate polarity, where ion pairs are present, is accounted for by photoinduced electron transfer in competition to trans → cis photoisomerization.

Download Full-text

Effective Singlet Oxygen Sensitizers Based on the Phenazine Skeleton as Efficient Light Absorbers in Dye Photoinitiating Systems for Radical Polymerization of Acrylates

Materials ◽

10.3390/ma14113085 ◽

2021 ◽

Vol 14 (11) ◽

pp. 3085

Author(s):

Ilona Pyszka ◽

Zdzisław Kucybała ◽

Beata Jędrzejewska

Keyword(s):

Quantum Yield ◽

Visible Light ◽

Triplet State ◽

Singlet Oxygen ◽

Radical Polymerization ◽

State Formation ◽

Flash Photolysis ◽

Comparative Method ◽

Aromatic Rings ◽

Light Absorbers

A series of dyes based on the phenazine skeleton were synthesized. They differed in the number of conjugated double bonds, the arrangement of aromatic rings (linear and/or angular system), as well as the number and position of nitrogen atoms in the molecule. These compounds were investigated as potential singlet oxygen sensitizers and visible light absorbers in dye photoinitiating systems for radical polymerization. The quantum yield of the singlet oxygen formation was determined by the comparative method based on the 1H NMR spectra recorded for the tested dyes in the presence of 2,3-diphenyl-p-dioxene before and after irradiation. The quantum yield of the triplet state formation was estimated based on the transient absorption spectra recorded using the nanosecond flash photolysis technique. The effectiveness of the dye photoinitiating system was characterized by the initial rate of trimethylolpropane triacrylate (TMPTA) polymerization. In the investigated photoinitiating systems, the sensitizer was an electron acceptor, whereas the co-initiator was an electron donor. The effectiveness of TMPTA photoinitiated polymerization clearly depended on the arrangement of aromatic rings and the number of nitrogen atoms in the modified phenazine structure as well as the quantum yield of the triplet state formation of the photosensitizer in the visible light region.

Download Full-text

Zum äußeren Schweratom-Effekt der Phosphoreszenz in nicht-fluoreszierenden aromatischen Verbindungen / The External Heavy-Atom-Effect of Phosphorescence in Non-fluorescing Aromatic Compounds

Zeitschrift für Naturforschung A ◽

10.1515/zna-1973-1119 ◽

1973 ◽

Vol 28 (11) ◽

pp. 1869-1870

Author(s):

M. Zander

Keyword(s):

Triplet State ◽

Aromatic Compounds ◽

Heavy Atom ◽

Quantum Yields ◽

Naphthalene Derivatives ◽

Heavy Atom Effect ◽

Atom Effect

Phosphorescence quantum yields of six non-fluorescing naphthalene derivatives have been measured in ethanol and ethanol-ethylbromide 1:1 at 77 °K. The observed enhancement of phosphorescence yield of four of these in the heavy atom solvent is explained with the assumption that the rate of the phosphorescence transition is increased relatively to the radiationless desactivation of the triplet state.

Download Full-text

Effect of Aggregation on Bacteriochlorin a Triplet-state Formation: A Laser Flash Photolysis Study¶

Photochemistry and Photobiology ◽

10.1562/0031-8655(2002)0760480eoaoba2.0.co2 ◽

2007 ◽

Vol 76 (5) ◽

pp. 480-485

Author(s):

Xavier Damoiseau ◽

Francis Tfibel ◽

Maryse Hoebeke ◽

Marie-Pierre Fontaine-Aupart

Keyword(s):

Triplet State ◽

State Formation ◽

Flash Photolysis ◽

Laser Flash Photolysis ◽

Laser Flash

Download Full-text

Mechanistic studies of aromatic ketone-sensitized photoreduction of bis(acetylacetonato)copper(II)

Canadian Journal of Chemistry ◽

10.1139/v83-147 ◽

1983 ◽

Vol 61 (5) ◽

pp. 801-808 ◽

Cited By ~ 25

Author(s):

Yuan L. Chow ◽

Gonzalo E. Buono-Core ◽

Bronislaw Marciniak ◽

Carol Beddard

Keyword(s):

Rate Constant ◽

Rate Constants ◽

Flash Photolysis ◽

Decay Rates ◽

Polynuclear Aromatic Hydrocarbons ◽

Aromatic Ketone ◽

Quantum Yields ◽

Triplet States ◽

Quenching Rate ◽

Triplet Energy

Bis(acetylacetonato)copper(II), Cu(acac)2, quenches triplet excited states of ketones and polynuclear aromatic hydrocarbons efficiently, but only aromatic ketones with high triplet energy successfully sensitize photoreduction of Cu(acac)2 in alcohols under nitrogen to give derivatives of aeetylacetonatocopper(I), Cu(acac). For the triplet state benzophenone-sensitized photoreduction of Cu(acac)2, the quantum yields of photoreduction (ΦC) and those of benzophenone disappearance (ΦB) were determined in methanol with various concentrations of Cu(acac)2. The values of the quenching rate constant, kq, determined from these two types of monitors on the basis of the proposed mechanism were in good agreement (6.89 ~ 7.35 × 109 M−1 s−1). This value was higher, by a factor of about two, than that obtained from the monitor of the benzophenone triplet decay rates generated by flash photolysis in the presence of Cu(acac)2. The quenching rate constants of various aromatic ketone and hydrocarbon triplet states by Cu(acac)2 were determined by flash photolysis to be in the order of the diffusion rate constant and the quantum yields of these photoreductions were found to be far from unity. Paramagnetic quenching, with contributions of electron exchange and charge transfer, was proposed as a possible quenching mechanism. For a series of aromatic ketone sensitizers with higher triplet energy, this mechanism was used to rationalize the observed high quenching rate constants in contrast to the low quantum yields of photoreduction.

Download Full-text

Flash photolysis of flavins. IV. Some properties of the lumiflavin triplet state

Journal of Bioenergetics and Biomembranes ◽

10.1007/bf01515980 ◽

1970 ◽

Vol 1 (2) ◽

pp. 181-192 ◽

Cited By ~ 65

Author(s):

Shiv P. Vaish ◽

Gordon Tollin

Keyword(s):

Triplet State ◽

Flash Photolysis

Download Full-text

The polymerization of styrene sensitized by molecules in the triplet state II. Kinetics and mechanism

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1959.0085 ◽

1959 ◽

Vol 251 (1264) ◽

pp. 4-26 ◽

Cited By ~ 10

Keyword(s):

Triplet State ◽

Aromatic Hydrocarbons ◽

Flash Photolysis ◽

Radical Addition ◽

Photochemical Reactions ◽

Kinetics And Mechanism ◽

Qualitative Investigation ◽

Initiation Mechanism ◽

Initial Formation ◽

Mechanism Of The Reaction

The kinetics and mechanism of the reaction between anthracene and styrene have been fully investigated. By means of flash photolysis techniques, it has been confirmed that it is the triplet state of anthracene which sensitizes the polymerization. It has also been shown that both triplet and unexcited singlet anthracene copolymerize with styrene, the former with a zero activation energy. The work has been extended to the polymerizations sensitized by pyrene and chrysene, and to the unsensitized photopolymerization of styrene. It has been shown that in every case an initiation mechanism, involving the initial formation of a triplet-monomer complex, satisfactorily explains the observed results. The copolymerization rates of pyrene and chrysene were undetectable; these results, coupled with those obtained for the copolymerization of anthracene with styrene, are in agreement with the conclusions of Kooyman & Farenhorst, Szwarc, and others, concerning the reactivity of olefinic and aromatic hydrocarbons to radical addition. Finally, a qualitative investigation of the photochemical reactions between the sensitizers, and cumene and 9 .10-dihydroanthracene, has been made.

Download Full-text