Effect of methyl substitution on the intramolecular triplet deactivation of p-methoxy-β-phenylpropiophenone

1991 ◽  
Vol 69 (12) ◽  
pp. 2053-2058 ◽  
Author(s):  
R. Boch ◽  
C. Bohne ◽  
J. C. Netto-Ferreira ◽  
J. C. Scaiano
Keyword(s):  
Charge Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Nanosecond Laser ◽  
Methyl Substitution ◽  
Intramolecular Quenching ◽  
Conformational Preferences ◽  
Key Words Laser ◽  
Nanosecond Laser Flash Photolysis

The photochemistry of several methyl-substituted p-methoxy-β-phenylpropiophenones (1–5) has been examined by nanosecond laser flash photolysis using 337-nm laser excitation. The ketone triplets decay by intramolecular β-aryl quenching of the carbonyl in a well-known process that is believed to involve charge transfer. Surprisingly, methyl substitution at the β-methylene group, which is not a participant in the deactiviation mechanism, causes a dramatic decrease in the triplet lifetime; the effect is attributed to different conformational preferences in ketones 1–3 and is rationalized on the basis of MMX calculations. Methyl substitution in the β-aryl ring affects the ease of oxidation of this ring and as a result induces changes in the kinetics for intramolecular charge transfer. This conclusion is further supported by electrochemical studies of ketones 1, 4, and 5. Key words: laser flash photolysis, triplet ketones, intramolecular quenching, charge transfer.

scholarly journals Onium salts improve the kinetics of photopolymerization of acrylate activated with visible light

RSC Advances ◽  
2020 ◽  
Vol 10 (42) ◽  
pp. 24817-24829 ◽  
Author(s):  
Janina Kabatc ◽  
Katarzyna Iwińska ◽  
Alicja Balcerak ◽  
Dominika Kwiatkowska ◽  
Agnieszka Skotnicka ◽  
...  
Keyword(s):  
Steady State ◽  
Visible Light ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Nanosecond Laser ◽  
Chemical Mechanisms ◽  
Onium Salts ◽  
Nanosecond Laser Flash Photolysis ◽  
Kinetics Of

The chemical mechanisms were investigated by steady state photolysis and nanosecond laser flash photolysis experiments. A mechanism for initiating polymerization using both onium salts is proposed here.

Photocatalytic Electron Transfer in Hybrid Titania Nanosheets Studied by Nanosecond Laser Flash Photolysis

2005 ◽  
Vol 34 (11) ◽  
pp. 1522-1523 ◽  
Author(s):  
Takashi Tachikawa ◽  
Tatsuto Yui ◽  
Mamoru Fujitsuka ◽  
Katsuhiko Takagi ◽  
Tetsuro Majima
Keyword(s):  
Electron Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Nanosecond Laser ◽  
Nanosecond Laser Flash Photolysis

Organic reactions in liquid crystalline solvents. 4. Nanosecond laser flash photolysis studies of intramolecular motions of rod-like solutes in liquid crystals

1986 ◽  
Vol 64 (6) ◽  
pp. 1130-1139 ◽  
Author(s):  
William J. Leigh
Keyword(s):  
Nematic Phase ◽  
Liquid Crystalline ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Orientational Order ◽  
Laser Flash ◽  
Viscous Drag ◽  
Nanosecond Laser ◽  
Nanosecond Laser Flash Photolysis ◽  
Nematic Solvent

The rates of triplet decay of a series of β-aryl-(4-alkoxypropiophenone)s in the smectic, nematic, and isotropic phases of 4′-butyl- and 4′-ethylbicyclohexyl-4-carbonitrile (BCCN and ECCN, respectively) have been measured over the 30–95 °C temperature range by nanosecond laser flash photolysis. The rates of triplet decay for these probe molecules in fluid solution are governed by the rates of Cα—Cβ bond rotation, which allows intramolecular quenching of the carbonyl triplet state by the β-aryl ring. The ketones are substituted with alkyl groups of varying length, shape, and flexibility in the para positions of the β-phenyl (H, n-hexyl, cyclohexyl) and benzoyl (meth-, n-pent-, and n-octoxy) rings. With the exception of β-phenyl-(4-methoxypropiophenone), for each ketone the Arrhenius parameters for triplet decay in the smectic phase of BCCN are similar to those in the nematic phase of the same solvent, and in all cases, the Arrhenius plots exhibit perfect continuity at the S—N transition temperature. A solvation model is tentatively advanced to explain these results. In the nematic phase of BCCN, the Arrhenius activation energy and entropy are significantly more positive than those in isotropic ECCN for all the ketones studied, but variations in the energetics of triplet decay in the nematic phase as a function of solute structure are parallelled in the isotropic solvent. Thus, the inhibiting effect of the nematic solvent on the bond rotations leading to intramolecular triplet quenching in these probes is attributed to the predominant influence of microviscosity (viscous drag) effects; the presence of solvent orientational order appears to have little or no effect on the intramolecular mobility of these ketones. The results and conclusions of earlier studies of unimolecular reactions in nematic solvents are discussed in light of these results.

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