Primary photochemical and photophysical processes in 2,2,4-trimethyl-1,2-dihydroquinolines

Malkin, Ya. N.; Pirogov, N. O.; Кузьмин, В. А.

doi:10.1016/0047-2670(84)80038-6

Cited by 31 publications

(10 citation statements)

References 4 publications

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“…The calculated value of the parameter 2k 3 /ε λ is 3-4 orders of magnitude lower than the corresponding values for hydrocarbon solutions [5,10,18]. The rate constant k 1 probably characterizes the exit of the radicals from the micellar core, where they are generated, into the Stern layer and the aqueous phase, where they recombine with the rate constant k 3 .…”

Section: Dhq Photolysis In the Micellar Solutions Of The Cationic Surmentioning

confidence: 75%

“…(2) and (3), A λ is the total absorbance registered at the wavelength λ, is the initial absorbance of the intermediate species i at the registration wavelength (the set of values at different wavelengths is the absorption spectrum of the species i), k i is the decay rate constant for the species i, l is the optical path length, and ε λ is the molar absorption coefficient of the species at the registration wavelength. In this study, ε λ in the CTAB micellar solutions was not determined, and the values of 2k 3 /ε λ were compared with the corresponding parameters obtained for hydrocarbon solutions [5,18] assuming that ε λ does not change significantly in micellar solutions. In flash photolysis experiments, bimolecular rate constants are determined with a factor of 1/ε λ ; that is, the calculated parameter is 2k 3 /ε λ .…”

Section: Dhq Photolysis In the Micellar Solutions Of The Cationic Surmentioning

confidence: 99%

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10.1007/s10975-008-2008-z

2000

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The kinetics of the photolysis of substituted 1,2-dihydroquinolines (DHQ) in micellar solutions was studied by steady-state and flash photolysis. The photolysis mechanism depends dramatically on the location of DHQ molecules in micelles, which is governed by the surfactant nature. In micellar solutions of the anionic surfactant sodium dodecyl sulfate (SDS), where the DHQ molecules are located in the Stern layer, the intermediate species decay kinetics follows a first-order law. When DHQ is in neutral form (pH 4-12), the rate constant of the intermediate carbocation decay increases from 25 to 198 s -1 with an increasing concentration of DHQ in micelles. The positive micellar catalysis is caused by the acceleration of the final product formation with the DHQ molecule via proton abstraction from the intermediate cation. The formation of several types of intermediate species-carbocations in the aqueous phase and aminyl radicals in micelles-is observed in micellar solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB) due to the preferential location of DHQ molecules in the micellar core. The carbocation decays via a pseudofirst-order reaction with a rate constant close to that in the aqueous solution. The lifetime of the DHQ aminyl radicals in the micellar solutions is longer by several orders of magnitude than the lifetime observed for homogeneous solutions of hydrocarbons and alcohols.

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Section: Dhq Photolysis In the Micellar Solutions Of The Cationic Surmentioning

confidence: 75%

Section: Dhq Photolysis In the Micellar Solutions Of The Cationic Surmentioning

confidence: 99%

10.1007/s10975-008-2008-z

2000

CrossRef Listing of Deleted DOIs

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“…Hence, the drastic decrease in the fluorescence lifetime in MeOH should increase the overall rate constant of nonradiative transitions (k NR ) in this solvent. We did not measure the ratio of the quantum yields of internal conversion and intersystem crossing in this work, but it was shown in [5] that internal conversion is the main channel of nonradiative energy deactivation (ϕ ISC < 0.02 in toluene). Therefore, we may assume that the variations in the rate constant of nonradiative transitions are determined mainly by changes in the rate constant of internal conversion.…”

Section: Methodsmentioning

confidence: 96%

“…In aprotic solvents and alcohols with C > 1, the homolytic cleavage of the N-H bond to give corresponding aminyl radicals was observed in the case of sec -DHQ [4]. The quantum yields of the homolytic photodissociation of the N-H bond in aprotic solvents upon excitation of the long-wavelength absorption band are low, and the fluorescence quantum yields are high [5,6]. This is accounted for by the fact that the reaction occurs from the first excited singlet rather than triplet state, and this process, as was shown earlier [5,7,8], has low efficiency.…”

mentioning

confidence: 98%

Primary Photophysical and Photochemical Processes in the Photolysis of 1,2-Dihydroquinolines in Different Solvents

Nekipelova

Кузьмин

2005

High Energy Chem

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1 Recently, it has been shown the photochemical transformations of alkyl and alkoxy substituted dihydroquinolines are very sensitive to the solvent nature, with the critical change of the reaction direction occurring on passing from aprotic solvents to water and methanol [1][2][3]. In aprotic solvents and alcohols with C > 1, the homolytic cleavage of the N-H bond to give corresponding aminyl radicals was observed in the case of sec -DHQ [4]. The quantum yields of the homolytic photodissociation of the N-H bond in aprotic solvents upon excitation of the long-wavelength absorption band are low, and the fluorescence quantum yields are high [5,6]. This is accounted for by the fact that the reaction occurs from the first excited singlet rather than triplet state, and this process, as was shown earlier [5,7,8], has low efficiency. N -Alkylated DHQ ( tert -DHQ) are photochemically stable in hydrocarbon solvents. In water and methanol, the photoinduced addition of solvent molecules to the double bond of the heterocycle occurs under irradiation without formation of intermediate radicals in the case of both sec-and tert -DHQ [1]. The reaction occurs from the excited singlet state. The process is accompanied by a drastic increase in the quantum yield of the reaction with a decrease in the quantum yield of fluorescence [3,6]. A carbocation formed in the reaction of proton transfer from the solvent molecule to the substrate in the excited singlet state to the C(3) atom of the heterocycle is the primary transient species observed in the flash photolysis of tert -DHQ. In the case of the sec -DHQ photolysis in MeOH, cyclic o -quinomethane imine is the primary transient species, which is formed as a result of the dou-1 e-mail: nekip@sky.chph.ras.ru ble proton transfer: from the solvent molecule to the substrate on the C(3) position and from the substrate N-H bond to the solvent molecule (Scheme 1).A study of the spectral characteristics of DHQ in different protic and aprotic solvents and their mixtures has shown that changes in the mechanism of photochemical reaction correlate with changes in absorption and fluorescence spectra [6]. Hydrogen bonding with a proton-donating solvent molecule plays the key role in this process. Since the reaction proceeds from the excited singlet state and the reaction and fluorescence quantum yields strongly depend on the solvent, the results of measurements of DHQ fluorescence lifetimes in different solvents and of the wavelength dependence of the fluorescence quantum yield presented in this work are very important for understanding the mechanism of the photophysical and photochemical processes occurring upon interaction of DHQ with light. EXPERIMENTAL 2,2,4,6-Tetramethyl-1,2-dihydroquinoline ( 1 ) (mp 42° C, Reakhim, Russia), 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline ( 2 ) (bp 150-152° C , 12 mmHg, synthesized according to a procedure described in [9] by reacting 1 with methyl iodide), 2,2,4-trimethyl-1,2-dihydroquinoline ( 3 ) (mp 18° C, synthesized in the condensation reaction of acetone with ...

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“…Polycyclic aromatic compounds, well-known as “polyarenes”, always remain as frontier candidates for photophysical studies since the introduction of photophysical measurements to the scientific community. − These molecules generally possess strong absorption in the near-UV and visible range and are highly emissive in most cases. ,, Thus, most of these molecules are cited as a classic reference for the explanation of basic photophysical aspects . Notably, the rigid molecular structure of these molecules does not corroborate the excited state decay through nonradiative pathways.…”

Section: Introductionmentioning

confidence: 99%

Manifestation of Unforeseen Superradiance Phenomenon from Phenanthrene and Chrysene Nanoaggregates

Manna

Nandi

2019

J. Phys. Chem. C

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The thin film and nanocomposite forms of polyacene and their derivatives have attracted extensive research attention in the recent few years. However, the thin film or nanostructure forms of nonlinearly attached polyaromatic compounds remain unattractive toward the scientific community, until now. Herein, the detail photophysical investigations have been presented for nanoaggregates of two nonlinearly attached polyaromatic molecules, namely, phenanthrene and chrysene. Upon aggregate formation, these materials shows 4−6 times enhancement in the extinction coefficient associated with the lowest energy transition. This is governed by a stronger transition dipole appearing through the correlated interaction of the transition dipole associated with the adjacent molecules present in the aggregates. The stronger transition dipoles also consequence significantly higher emission yield by promoting the faster radiative decay, as compared to that of the monomeric form. The enhanced radiative decay rate and its dependence upon sample temperature certify the presence of the superradiance property of these materials. Most importantly, this is the first report to detect the superradiant property of these nonlinearly attached polyaromatic molecular systems in any physical form and thus deserves remarkable research interest of the scientific community in the near future.

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Primary photochemical and photophysical processes in 2,2,4-trimethyl-1,2-dihydroquinolines

Cited by 31 publications

References 4 publications

10.1007/s10975-008-2008-z

10.1007/s10975-008-2008-z

Primary Photophysical and Photochemical Processes in the Photolysis of 1,2-Dihydroquinolines in Different Solvents

Manifestation of Unforeseen Superradiance Phenomenon from Phenanthrene and Chrysene Nanoaggregates

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