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Relevant academic research and scientific papers

Transient Spontaneous Raman Study of Photoionization Kinetics at the Hydrocarbon/Water Interface in Micellar Solutions

Transient spontaneous Raman spectroscopy (416 nm) has been used to observe the kinetics of TMB+ and TMB2+ ions following photoionization of tetramethylbenzidine (TMB) in aqueous micellar solutions.The ground-state TMB pKa values are shifted by micellar solubilization in the directions predicted by calculated surface pH values.In SDS micelles, the TMB+ ion initially produced is stabilized by negative surface groups.No time evolution of the TMB+ Raman spectrum occures, and bimolecular ion reactions are not observed.However, in CTAB micelles, TMB+ is destabilized by positive surface groups.The TMB+ Raman spectrum evolves on the 10-6-s time scale, suggesting that the ion has moved into the Stern layer and is assymmetrically solvated.On the 10-4-s time scale, TMB2+ appears from disproportionation of two TMB+ ions.Positive spectral identifications are facilitated by comparison with spectra obtained by chemical oxidation in various enviroments.

Photoionization of N,N,N′N′-tetramethylbenzidine in chromium silicoaluminophosphate microporous materials

Silicoaluminophosphate (SAPO) microporous materials with Cr incorporated by ion-exchange and by direct synthesis were impregnated with N,N,N′N′-tetramethylbenzidine (TMB) and photoionized with 300 nm light at room temperature. TMB cation radicals are produced and characterized by electron paramagnetic resonance and diffuse reflectance spectroscopy. The photoyield is negligible for H-SAPO-n materials indicating that the chromium ion serves as an electron acceptor to enhance the yield of photoproduced TMB cation radical. The photoyield is dependent on the valence, amount and reduction potential of the metal ion and on the pore size of the SAPO material. Chromium SAPO materials are efficient hosts for the formation and stabilization of TMB cation radicals.

Electron Spin Resonance and Electron Spin-echo Modulation Studies of 5-Doxylstearic Acid and N,N,N',N'-Tetramethylbenzidine Photoionization in Sodium Dodecylsulphate Micelles. Effects of 15-Crown-5 and 18-Crown-6 Ether addition

Electron spin-echo modulation (e.s.e.m.) and electron spin resonance (e.s.r.) spectra of the photogenerated N,N,N',N'-tetramethylbenzidine (TMB) cation radical and 5-doxylstearic acid (5-DSA) in frozen micellar solutions of sodium dodecylsulphate containing 15-crown-5 and 18-crown-6 ethers in D2O and H2O have been studied as a function of the crown ether concentrations.Modulation effects due to 5-DSA interactions with water deuteriums give direct evidence that both crown ethers are mainly located at the micellar interface and that their interaction causes a decrease of hydration of the micellar interface.Modulation effects from TMB+ interaction with water deuteriums indicate that the TMB molecule moves toward the interfacial region when the sodium cation is complexed by the crown ether to decrease the local ionic strength in the interfacial region.The efficiency of charge separation upon TMB photoionization increases ca. 10percent with crown ether addition, and correlates with the increased TMB+-water interactions.The sodium cation complexation by the crown ether to change the charge distribution and ionic strength at the micellar interface seems to cause the interfacial hydration changes that promote the photoionization efficiency.

Electron Spin Resonance and Electron Spin Echo Modulation Studies of N,N,N',N'-Tetramethylbenzidine Photoionization in Frozen Micellar Solutions: Structural Effect of 1-Butanol Addition to Sodium and Tetramethylammonium Dodecylsulfate and Dodecyltrimethylammonium Chloride Micelles

The electron spin echo modulation (ESEM) and electron spin resonance (ESR) spectra of the photogenerated N,N,N',N'-tetramethylbenzidine cation radical (TMB+) in frozen micellar solutions of sodium and tetramethylammonium dodecylsulfate (SDS and TMADS, respectively) as well as dodecyltrimethylammonium chloride (DTAC) have been studied as a function of 1-butanol (1-BuOH) concentration from 0 to 200 mM.A 5-doxylstearic acid spin probe has also been used in the ESEM experiments.The efficiency of TMB photoionization has been determined from ESR data, while ESEM analysis has given information about micelle hydration and aqueous interactions of TMB+.The variations observed with 1-BuOH addition depend on the micellar charge and the nature of the counterion in dodecylsulfate micelles.The main findings are that (1) hydration of TMADS micelles decreases from 0 to 200 mM 1-BuOH, while hydration of SDS and DTAC micelles increases somewhat from 0 to 100 mM and remains constant from 100 to 200 mM 1-BuOH, and (2) the efficiency of charge separation upon photoionization of TMB can be increased by alcohol addition in SDS micelles but not in TMADS and DTAC micelles.The results are interpreted primarily in terms of the effect of added alcohol on the surfactant headgroup density.

Photochemical Behaviour of N,N,N',N'-Tetramethylbenzidine and its Protonated Forms in Sodium Dodecyl Sulphate Anionic Micelles under 337 nm Laser Irradiation

Continuous 337 nm laser excitation of N,N,N',N'-tetramethylbenzidine (TMB) in 0.1 mol dm-3 sodium dodecyl sulphate micelles produces monophotonic ionization of the molecule.A study of the photoionization process has resulted in the following new results: (1) the radical-cation quantum yield decreases with adsorbed light because of its spectral overlap with TMB and its simultaneous photodestruction during irradiation, (2) partial regeneration of the TMB absorption band after radical-cation decay suggests that a principal mode of radical decay is through a disproportionation reaction, (3) the photoionization yield is affected by the degree of protonation of TMB, increasing with increasing bulk pH, and (4) diprotonated TMB, TMBH22+, photodecomposes into TMB2+.

OPTICAL ABSORPTION, ELECTRON SPIN RESONANCE, AND ELECTRON SPIN ECHO STUDIES OF THE PHOTOIONIZATION OF TETRAMETHYLBENZIDINE IN CATIONIC AND ANIONIC SYNTHETIC VESICLES: COMPARISON WITH ANALOGOUS MICELLAR SYSTEMS.

The photoionization of N,N,N prime ,N prime -tetramethylbenzidine (TMB) in dihexadecylphosphate anionic vesicles and in dioctadecyldimethylammonium chloride cationic vesicles has been studied by optical absorption and electron spin resonance in liquid and frozen solutions. The TMB cation has been observed to be stabilized in both types of vesicles. The photoionization efficiency is about twofold greater in the cationic vesicles compared to the anionic vesicles. Shifts in the optical absorption maximum between micellar and vesicle solutions indicate that TMB is in a less polar environment in the vesicle systems. Electron spin echo modulation spectrometry has been used to detect TMB cation-water interactions that are found to be weaker than in previously studied micellar solutions. This is consistent with the optical absorption results and with an asymmetric solubilization site for TMB and TMB** plus within the vesicular structure. A new absorption in the photoionized vesicles is assigned to a nonparamagnetic diamine-diimine charge-transfer complex between two TMB cations in the same vesicle. This complex is not formed in micellar systems.

Metallopolymer Photochemistry. Photophysical, Photochemical, and Photoelectrochemical Properties of (bpy)2RuII< Sites Bound to Poly(4-vinylpyridine)

The photochemical and photophysical properties of the polymer-bound chromophore Ru(bpy)2(PVP)22+ (PVP is poly(4-vinylpyridine)) have been investigated in homogeneous solution.Results have been obtained with polymers both dilute and concentrated in chromophore.Lifetime and quantum yield data are interpreted in terms of models of excited-state behavior previously proposed for analogous mopnomeric poly(pyridyl) complexes of Ru(II).Excited-state sites within the metallopolymers undergo oxidative and reductive electron-transfer quenching.The quenching reaction were investigated by Stern-Volmer quenching and conventional microsecond flash photolysis.Sensitization of n-TiO2 to visible light has been observed on a semiconductor coated with a film of the metallopolymer.