Laser photoionization and light-initiated redox reactions of tetramethylbenzidine in organic solvents and aqueous micellar solution. [Correlation between the photochemical yields of triplet and cation radical formation]

Journal Article · Wed Jun 09 04:00:00 EDT 1976 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00428a027· OSTI ID:7182444

Alkaitis, S A; Graetzel, M

The 347.1-nm ruby laser photolysis of N,N,N',N'-tetramethylbenzidine (TMB) was studied in organic solvents, i.e., cyclohexane and methanol, and micellar solution. The main photoreaction in the organic solvents is triplet formation. The energy of the triplet was determined as 2.7 +- 0.05 eV. The triplet spectrum has an absorption maximum at 475 nm and the extinction coefficient at this wavelength is (4.1 +- 0.3) x 10/sup 4/ M/sup -1/ cm/sup -1/ in methanol. It is almost identical with the spectrum of TMB/sup +/ cation radicals. In methanol small amounts of ions, TMB/sup +/, and solvated electrons are produced monophotonically by the laser pulse, the relative efficiency of ion vs triplet formation being r = 0.17. The r value observed in micellar solution of sodium lauryl sulfate (NaLS) is 36 times greater, indicating pronounced enhancement of the photoionization process by the anionic micelles. Hydrated electrons and TMB/sup +/ cation radicals are also produced by sunlight irradiation of TMB solution in NaLS micelles and possible utilization of the micellar effects are discussed. TMB triplets were found to have strongly reducing properties and in methanolic solution transfer an electron to acceptors such as duroquinone (DQ) and Eu/sup 3 +/. The rate constants for the transfer processes are 2.3 x 10/sup 10/ and 6.4 x 10/sup 9/ M/sup -1/ s/sup -1/ for duroquinone and Eu/sup 3 +/, respectively. These light-initiated redox processes are reversible, the back transfer from DQ/sup -/ and Eu/sup 2 +/ to TMB/sup +/ occurring at specific rates of 2 x 10/sup 9/ and 1.4 x 10/sup 7/ M/sup -1/ s/sup -1/, respectively. Similar redox processes are observed in NaLS micellar solution, the intramicellar forward and backward electron transfer to Eu/sup 2 +/ and from Eu/sup 2 +/ occurring with specific rates of 2.3 x 10/sup 7/ and 8.5 x 10/sup 2/ s/sup -1/, respectively.

• Research Organization: Hahn-Meitner-Institut fuer Kernforschung, Berlin
• OSTI ID: 7182444
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 98:12; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140500 -- Solar Energy Conversion
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ABSORPTION SPECTROSCOPY
ALCOHOLS
ALKANES
AMINES
AROMATICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
CONVERSION
CYCLOALKANES
CYCLOHEXANE
DECOMPOSITION
ENERGY CONVERSION
HYDROCARBONS
HYDROXY COMPOUNDS
IONIZATION
LASERS
METHANOL
MICELLAR SYSTEMS
MULTIPLETS
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOIONIZATION
PHOTOLYSIS
REDOX REACTIONS
RUBY LASERS
SOLAR ENERGY CONVERSION
SOLID STATE LASERS
SPECTROSCOPY
TRIPLETS
YIELDS