Showing papers by "Prashant V. Kamat published in 1987"

Photochemistry of 3,4,9,10-perylenetetracarboxylic dianhydride dyes. 3. Singlet and triplet excited-state properties of the bis(2,5-di-tert-butylphenyl)imide derivative

Abstract: Fluorescence lifetime and triplet-state spectral, kinetic, and energetic properties are reported for the first time for a perylenebis(dicarboximide) dye, N,N'-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenebis(dicarboximide) (DBPI). The fluorescence lifetime (3.8 +/- 0.2 ns), quantum yield (greater than or equal to 0.95), and singlet-state energy (54 +/- 1 kcal mol/sup -1/) were determined for DBPI in a variety of organic solvents (24/sup 0/C). Triplet sensitization was used to characterize the triplet state of DBPI by laser flash photolysis and pulse radiolysis. The triplet-triplet absorption spectrum of DBPI had a maximum in the range 495-505 nm with an extinction coefficient of (6.3 +/- 0.7) x 10/sup 4/ M/sup -1/ cm/sup -1/, and the triplet-state energy and lifetime were 27.5 +/- 2 kcal mol /sup -1/ and approx. = 100 ..mu..s, respectively. Direct photoexcitation produced the DBPA triplet with very low quantum yields (<0.001). Excimerlike fluorescence spectral and lifetime data for DBPI in the solid state are also presented.

Photoelectrochemistry in particulate systems. 6. Electron-transfer reactions of small cadmium sulfide colloids in acetonitrile

Abstract: Small colloidal CdS particles (particle diameter < 25-42 A) have been prepared in acetonitrile and their absorption and emission properties characterized. A transient bleaching was observed when CdS colloids were subjected to bandgap excitation with a 355-nm laser pulse. The recovery of the bleaching which consisted of at least two components has been attributed to the recombination of trapped charge carriers and to the process of anodic corrosion. The red emission of CdS colloid can be quenched with an electron scavenger such as methylene blue. The quantum yield for the reduction of oxazine and thiazine dyes varied from 0.04 to 0.08 and was dependent on the reduction potential of the dye. The electron-transfer reactions of CdS colloids have been investigated by using nanosecond laser flash photolysis and microwave absorption techniques.

Transient photobleaching of small cadmium selenide colloids in acetonitrile. Anodic decomposition

Abstract: Small CdSe colloids (particle diameter 30-50 A) that exhibit quantization effects are prepared in acetonitrile. The authors show intensive transient photobleaching in the 370-500-nm region and transient absorption around 300 and 500-600 nm immediately after bandgap excitation of the semiconductor. The nature and kinetic behavior of the transient photobleaching, which is attributed to the trapped charge carriers, are elucidated by investigating the influence of laser dose and various hole and electron scavengers.

Fluorescence emission as a probe to investigate electrochemical polymerization of 9-vinylanthracene

Abstract: The cationic polymerization of 9-vinylanthracene can be initiated at a transparent SnO/sub 2/ electrode with the application of anodic potentials (E > 1.1 V vs. saturated sodium chloride calomel electrode) in acetonitrile solutions. The excimer emission (emission maximum approx.500 nm) of poly(9-vinyl-anthracene) which is distinguishable from the monomer fluorescence emission (emission maxima 410, 430 nm) has been used to probe the electrochemical polymerization process directly. The in situ spectroelectrochemical technique, which would be useful in obtaining kinetic and mechanistic information of the electropolymerization process, is described.

Electron transfer reactions. Reaction of nitrones with potassium

Abstract: Treatment of nitrones (1a–d, 26a,b, 34, 49) with potassium in tetrahydrofuran (THF) gives rise to radical anion (2a–d, 27a,b, 35, 50) and dianion intermediates (3a–d, 28a,b, 36) through electron transfer reactions. These intermediates undergo further transformations to give a variety of products. Thus, the aldehydonitrones (1a–d) give the corresponding aldehydes (10a–c), carboxylic acids (25a–c), and azobenzenes (19a,d), whereas the ketonitrones (26a,b) give deoxygenation products (31a,b). The nitrone 34 gave a mixture of products consisting of benzoic acid (25a), dibenzyl (48), the dimeric product 38, and tetraphenylpyrazine (46), whereas 49 did not give any isolable product. Cyclic voltammetric studies have been employed to measure the reduction potentials for both one-electron and two-electron transfer processes, leading to the radical anions and dianions respectively. These intermediates have been characterized through their electronic spectra and they were quenched by oxygen. Pulse radiolysis of the ...

Photoelectrochemistry in particulate systems. 5. Visible light‐induced polymerization of 1‐vinylpyrene in semiconductor suspensions

Abstract: Photoelectrochemical polymerization of 1-vinylpyrene has been achieved in a semiconductor photocatalyst suspension under visible light irradiation (λ > 480 nm). Bandgap excitation of CdS, CdSe or Fe2O3 led to the oxidation of 1-vinylpyrene, which initiated the polymerization process. A 25–47% yield of poly(1-vinylpyrene) could be obtained upon irradiation of these semiconductor photocatalyst suspensions with 1-vinylpyrene in acetonitrile. Dependence of the polymer yield on various experimental conditions is described.

Electron transfer reactions. Reaction of Δ2-oxazoline-5-ones and related substrates with potassium

Abstract: The reaction of several Δ2-oxazolin-5-ones (1a–c, 12) and bioxazolinones (17, 26) with potassium in THF has been investigated. Treatment of 1a with potassium in THF gave a mixture of dibenzamide (1...

Electron transfer reactions. Reaction of nitrones with potassium1

Abstract: On propose des mecanismes mettant en jeu la formation initiale d'intermediaires sous forme de radicaux anions