TMPD photoionization

A study of the photoionization of tetramethyl-/ -phenylenediamine (TMPD) in solution [49] showed the dependence of the wavelength of ionization onset on the energy Fq of the sol-... 

In summary, the photooxidation of TMPD is extremely complex and several independent photoionization mechanisms appear to be operative, depending on the solvent polarity and temperature it would seem that further studies, particularly on the kinetics of formation and decay of the triplet state under different experimental conditions, are warranted. 

Figure 12. ESR spectrum during photoionization of sample containing 15 mole % CHSCN and 0.02 mole % TMPD in MTHF at 77°K.

Finally, we wish to draw attention to the comparison in Figure 7 between the optical bleaching rates of (e ) in y-irradiated MTHF and in the photoionized MTHF-TMPD system under the same conditions, using red light (A > 600 n.m.). The decay rate is slightly greater for the y-irradiated MTHF, but this difference is minor compared with the much faster decay which is observed when more than 5 mole % CH3CN is present in the matrix of the y-irradiated sample. 

Two papers have appeared on the photoionization of A,yV,iV, jV -tetramethyl-/j-phenylenediamine (TMPD) in various solvents. Emission and absorption... 

Some photoionizations occur only in halogenomethane solvents whereas in other solvents (e.g. ethanol, benzene) only fluorescence occurs in the halogenated solvents ionization is monophotonic. This is the case with di- and tetraphenyl-p-phenylenediamine in chloroform and carbon tetrachloride (Fitzgerald et al., 1971), and with TMPD in chloroform, bromoform, methylene bromide and chloride (Meyer, 1970), and dimethylaniline in bromobenzene (Gradowski and Latowski, 1974 et al., 1972). Electron transfer may occur from the excited aromatic singlet to ground state solvent [(54) and... 

PLLA (b), and main-chain tertiary radicals of PLLA (c) via photoionization of TMPD, according to Sakai et al. [17]. 

Katoh, R., Lacmann, K., and Schmidt, W. E, Effect of high pressure on photoionization of TMPD in liquid 2,2-dimethylbutane, Chem. Phys., 195, 457, 1995. 

From the intercept at E = 0 of the linear portion of the photocurrent, the quantum yield of free ions is obtained. The zero field quantum yield is a function of the photon energy and of the nature of the solvent. In Figure 7, the spectral dependence of the quantum yield for photoionization of TMPD in three solvents is shown. Roughly, a correlation exists between the quantum yield and the electron mobility of each solvent. In tetramethylsilane = 100 crrPV s ) higher quantum yields are measured as compared to n-hexane (Pei = 0.1 cm2V" s" ). Aromatic molecules were studied in a variety of hydrocarbon solvents (Choi et al., 1982 Holroyd et al. 1983, 1984). Some results for the photoionization energy are summarized in Table 4. 

Figure 7 Zero field quantum yield for photoionization of TMPD in solution at room temperature. (Redrawn from the data of Choi, H.T., Sethi, D.S., and Braun, C.L., /. Chem. Phys., 17, 6027, 1982.)...

Bullot, J., Cordier, R, and Gauthier, M., The quenching effect of an external electric field on the fluorescence of TMPD in 2,2,4-trimethylpentane excited above the photoionization threshold, J. Chem. Phys., 69,1374,1978. 

The ionization energy of TMPD in solid and liquid solutions of hydrocarbons was studied by biphotonic ionization and detection of recombination fluorescence (Bullot and Gauthier, 1976). Generally, the photoionization threshold decreased on going from the solid to the liquid phase. The following sequence was observed ... 

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