420 research outputs found
Electronic absorption spectrum and decay kinetics of the benzyl radical in solution
No full textDuring studies of the transient optical spectra of the intermediates produced in the flash photolysis of various substituted aromatic compounds in aqueous solution (L. J. Mittal, J. P. M., and E. H., unpublished work), in addition to the characteristic spectrum of the benzyl radical with λmax at 318 nm and at â^¼307 nm we observed a strong absorption at wavelengths below 290 nm
Solvatochromism, aggregation and photochemical properties of Fullerenes, C<SUB>60</SUB> and C<SUB>70</SUB>, in solution
No full textFullerenes, C60 and C70, display interesting physicochemical properties in solutions, especially due to their unique chemical structures and their good electron accepting abilities. Solubility of fullerenes in different organic solvents and their unusual solvatochromic behavior, the ability of the fullerenes to form aggregates in solutions, and their electron transfer and charge transfer interactions with variety of electron donors, are the subjects of extensive research activities for more than one decade. Many research groups including ours have contributed substantially in the understanding of the solvatochromism, aggregation behavior, and the photoinduced electron transfer and charge transfer chemistry of fullerenes, in condensed phase. Present article is aimed to summarize the important results reported on the above aspects of fullerenes, subsequent to the earlier report from our group. (D.K. Palit and J.P. Mittal, Full. Sci. & Tech. 3, 1995, 643-659)
Electron-transfer and excited-state properties of radiolytically generated transients of acridine(1,8)dione dyes in an organic matrix
No full textPulse radiolysis technique has been employed to generate and investigate electron and energy transfer reactions involving acridine(1,8)dione dyes in hydrocarbons. The transient absorption spectra obtained on pulse radiolysis of N2-saturated solution in 1,2-dichloroethane are assigned to solute radical cation. The radical cations undergo charge transfer reaction with tetramethyl-p-phenylenediamine and triethyl amine. The transient absorption spectra in N2-saturated solution in benzene are assigned to triplet-triplet absorption. It was observed that biphenyl, p-terphenyl and benzophenone triplets undergo energy transfer to methyl and phenyl substituted acridine(1,8)dione dyes generating the triplets of the acceptor. With H substituted acridine(1,8)dione dye, benzophenone and chloranil triplets favor electron-transfer followed by H+ transfer reaction forming benzophenone ketyl and chloranil semiquinone radicals respectively
Solvatochromism, aggregation and photochemical properties of Fullerenes, C<SUB>60</SUB> and C<SUB>70</SUB>, in solution
No full textFullerenes, C60 and C70, display interesting physicochemical properties in solutions, especially due to their unique chemical structures and their good electron accepting abilities. Solubility of fullerenes in different organic solvents and their unusual solvatochromic behavior, the ability of the fullerenes to form aggregates in solutions, and their electron transfer and charge transfer interactions with variety of electron donors, are the subjects of extensive research activities for more than one decade. Many research groups including ours have contributed substantially in the understanding of the solvatochromism, aggregation behavior, and the photoinduced electron transfer and charge transfer chemistry of fullerenes, in condensed phase. Present article is aimed to summarize the important results reported on the above aspects of fullerenes, subsequent to the earlier report from our group. (D.K. Palit and J.P. Mittal, Full. Sci. & Tech. 3, 1995, 643-659)
Light Emission from the Dissolution of Gamma Irradiated Alkali Halides in Water
No full textWe have been studying the primary processes in the radiation chemistry of aqueous and organic systems. Evidence has been accumulating for the presence of correlated ion pairs in the irradiated liquid and frozen aqueous solutions. Reactions of the mobile electrons and holes with the appropriate scavengers have been found to be interdependent. In order to explain the data, it was suggested that the primarily formed electrons and holes are not randomly distributed in the system, but instead move about as correlated electron-hole pairs which may be imagined as solid state excitons. I wish to report here some of our recent experimental evidence pointing towards the possible involvement of triplet excitons of Frenkel type. When gamma irradiated alkali halides are dissolved in water, stored energy is transferred to the solvent. Earlier studies of light emission from this process have been verified and extended
Different channels of hydroxyl radical reaction with aryl sulfides: effect of the substituents
No full textIn a neutral aqueous solution of (phenylthio)acetic acid, the hydroxyl radical is observed to react with a bimolecular rate constant of 7.2 × 109 dm3 mol-1 s-1, and the transient absorption bands are assigned to •OH radical addition to benzene and sulfur with rough estimated values of 50 and 40%, respectively. The reaction of the •OH radical with diphenyl sulfide (k = 4.3 × 108 dm3 mol-1 s-1) is observed to take place with the formation of the solute radical cation, OH-adduct at sulfur, and benzene with rough estimated values of 12, 28, and 60%, respectively. The transient absorption bands observed on reaction of the •OH radical, in neutral aqueous solution of 4-(methylthio)phenyl acetic acid, are assigned to solute radical cation (λ max = 550 and 730 nm), OH-adduct at sulfur (λ max = 360 nm), and addition at benzene (λ max = 320 nm). The fraction of •OH radical reacting to form a solute radical cation is observed to increase with increasing concentration of acid, and in highly acidic solutions, the solute radical cation is the only transient species formed on reaction of •OH radical with these sulfides
Structure-reactivity studies on the nature of transients formed on reaction of <SUP>•</SUP>OH radicals with chloroiodoalkanes in aqueous solution
No full textThe transient optical absorption bands (λ max= 315 and 345 nm) formed on reaction of •OH radicals with 1-chloro-3-iodopropane in N2O-saturated neutral aqueous solutions have been assigned to an OH-adduct formed between iodine atom and OH radicals (t½= 1.5 µ s, Î μ 350= 2.46 × 103 dm3 mol-1 cm-1). In acidic solutions, iodine-centred radical cations (λ max= 345 nm, t½= 4.0 µ s, Î μ 345= 2.41 × 103 dm3 mol-1 cm-1) are formed at low solute concentrations and dimer radical cations (λ max= 430 nm, t½= 16.0 µ s, Î μ 430= 6.7 × 103 dm3 mol-1 cm-1) at high solute concentrations. In chloroiodomethane, the •OH radicals do not seem to form OH-adducts in neutral aqueous solutions. In acidic solutions, intramolecular radical cation (λ max= 430 nm, t½= 8.0 µ s, Î μ 430= 2.63 × 103 dm3 mol-1 cm-1) with oxidized iodine and chlorine is observed. The intermolecular dimer radical cations are formed at high solute concentration (λ max= 500 nm)
Hydroxyl radical induced reactions in aqueous solutions of halogenated benzenes: effect of electronegativity of halogen
No full textThe √ OH radicals, generated by radiolysis, are found to react only in acidic conditions with halogenated benzenes by an electron transfer mechanism. The concentration of acid, at which solute radical cation of halogenated benzenes appear, is observed to depend strongly on the nature and number of halogen atoms in halogenated benzenes. A linear increase in the acid concentration required for solute radical cation formation is observed with electronegativity of halogen
Excited state dynamics of Michler's ketone: a laser flash photolysis study
No full textSteady state absorption and fluorescence as well as the time resolved absorption studies in the pico and subpicosecond time domain have been performed to characterize the excited singlet and triplet states of Michler's ketone (MK). The nature of the lowest excited singlet (S1) and triplet (T1) states depends on the polarity of the solvent - in nonpolar solvents they have either pure nπ∗ character or mixed character of π ∗ and π π ∗ states but in more polar solvents the states have CT character. Concentration dependence of the shapes of the fluorescence as well the excited singlet and triplet absorption spectra provide the evidence for the association of the MK molecules in the ground state
Pulse radiolysis investigations on electron-transfer reactions in aqueous solutions of substituted alkyl sulfides
No full textThe transient optical absorption band (λ max= 345 nm, t1/2= 4.0 µ s, ε = 2.6 × 103 dm3 mol-1 cm-1) formed on pulse radiolysis of N2O-saturated dilute neutral aqueous solutions of dimethyl 3,3'-thiodipropionate (DTDP) is assigned to an •OH-adduct. The rate constant for the reaction of •OH radicals has been determined to be 1.4 × 1010 dm3 mol-1 s-1. At higher solute concentrations the •OH-adduct is converted to sulfur-centred dimer radical cations (λ max= 510 nm, ε = 4.9 × 103 dm3 mol-1 cm-1, t1/2= 14.0 µ s). In acidic solutions, only dimer radical cations are formed. In neutral aqueous solutions of 3,3'-thiodipropanol (TDP)·OH radicals are able to bring about one-electron oxidation, forming intramolecular radical cations with p-orbital overlap between the oxidized sulfur and oxygen (λ max= 420 nm, t1/2= 17 µ s, ε = 2.6 × 103 dm3 mol-1 cm-1). In acidic solutions, sulfur-centred dimer radical cations are formed (λ max= 510 nm, t1/2= 12 µ s, ε = 6.3 × 103 dm3 mol-1 cm-1). In the presence of halide ions, the oxidized sulfur in DTDP and TDP stabilizes by formation of an S∴X type species
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