calculations of ∆G . Table 4 summarizes the reversible reduc-
5 G. H. Brown, B. Graham, P. W. Vittum and A. Weissberger, J. Am.
el
Chem. Soc., 1951, 73, 913.
tion potentials measured and the calculated ∆G values for the
el
6
7
8
E. B. Knott and P. J. S. Pauwels, J. Org. Chem., 1968, 33, 2120.
Z. Kucybała and J. P a˛ czkowski, Polymer, 1993, 34, 1558.
O. Valdes-Aquilera, C. P. Phatak, J. Shi, D. Watson and D. C.
Neckers, Macromolecules, 1993, 25, 541.
AMDs tested. The ∆G values are calculated for both singlet
el
and triplet states of the dyes.
Data in Table 4 show that the intermolecular electron trans-
fer process is thermodynamically allowed, both via singlet and
triplet states. However, it is necessary to emphasize that the
secondary processes leading to the final product formation are
9 W. F. Smith and B. W. Rosster, J. Am. Chem. Soc., 1967, 89, 717.
10 M. Takuji, M. Akihiro and A. Youichi, J. Soc. Photogr. Sci. Technol.
Jpn., 1986, 49, 393.
11 M. Takuji, M. Akihiro and A. Youichi, J. Soc. Photogr. Sci. Technol.
Jpn., 1987, 50, 128.
2 M. Takuji, O. Takanori and A. Youichi, J. Soc. Photogr. Sci.
Technol. Jpn., 1989, 52, 532.
13 N. Grossman, V. Wehner, A. Weise and B. Winnig, J. Prakt. Chem.,
1988, 330, 204.
34
still not clear.
One more question arises when one considers the Marcus
35
1
treatment of the PET reaction of AMDs bleaching. Fig. 11
illustrates the relationship between the thermodynamic driving
force, ∆GЊ, of the PET of the photoreduction process and the
rate constants of the bleaching. From Fig.11 it can be seen that
1
1
1
4 J. Gaca, K. Kozłowski, M. Trzci n´ ska and Z. Kucybała, J. Prakt.
Chem., 1986, 328, 149.
5 D. P Maier, G. P. Hopp and T. H. Regan, Org. Mass Spectrom.,
Ϫ1
in the range of about 20 kcal mol one sees a plateau indicat-
ing that the reaction is not directly controlled by the electron
transfer process but is probably controlled by a combination of
several factors, e.g. the quantum yield of intersystem crossing
and the rates of processes subsequent to the photoinduced
electron transfer.
1
969, 2, 1289.
6 These specific conditions of photobleaching process are prescribed
by the conditions required during a photopolymerization using this
technique.
1
1
1
7 A. P. Schaap, A. L. Thayer, E. C. Blossey and D. C. Neckers, J. Am.
Chem. Soc., 1975, 97, 3741.
8 E. C. Blossey, D. C. Neckers, A. L. Thayer and A. P. Schaap, J. Am.
Chem. Soc., 1973, 95, 5820.
9 J. P a˛ czkowski, D. C. Neckers and B. P a˛ czkowska, Macromolecules,
1986, 19, 863.
7
We have shown earlier that AMDs in the presence of
N-phenylglycine are able to photoinitiate free radical poly-
20
merization. PET reactions of amines yield amine radical
cations, that after deprotonation give α-amino radicals which,
usually after cross-coupling between radical pairs terminate the
photoreduction. However, in very reactive solutions of polyol
acrylates some of the free radicals can start a chain reaction of
vinyl polymerization that competes with the color-loss process.
In summary it is important to emphasize that changes in the
dye structure are translated into changes in the rate of photo-
bleaching. The introduction of heavy atoms into a dye molecule
20 R. K. Summerbell and D. J. J. Berger, J. Am. Chem. Soc., 1959, 81,
33.
1 (a) V. Nagarajan and R. W. Fessenden, J. Phys. Chem., 1985, 89,
330; (b) K. Bobrowski, B. Marciniak and G. L. Hug, J. Am. Chem.
6
2
2
2
Soc., 1992, 114, 10279.
2 In a classical system development involves reduction of the silver
and in color photography it is the consequent oxidation of the
developer which reacts with color coupler to produce an image
dye. A typical system involves a derivative of benzene-1,4-diamine
as developer; see: R. P. Wayne, Principles and Applications of
Photochemistry, Oxford University Press, Oxford, 1988.
3 W. F. Smith, Jr., J. Phys. Chem., 1964, 68, 1501.
only slightly increases the bleaching efficiency. Introduction of
3
the CH group into the R position should decrease the freedom
3
of the phenyl group rotation and as a result decrease the rate of
nonradiative deactivation of the excited state and increase the
2
2
4 C. Reichard, Solvents and Solvents Effects in Organic Chemistry,
VCH, Weinheim, 1988.
26
rate of the bleaching process. However, after Herkstroeter, the
introduction of the methyl groups into the ortho positions of
the aromatic ring, attached to the azomethine nitrogen atom,
accelerates the rate of azomethine group isomerization. Signifi-
cant influence of the AMD structure on photobleaching rates is
observed only when the branching of the dye is limited and less
distinct when a strong electron withdrawing group is substi-
25 B. Strehmel, H. Seifert and W. Rettig, J. Phys. Chem., 1997, 101,
2
232.
2
2
6 W. G. Herkstroeter, J. Am. Chem. Soc., 1973, 95, 8686.
7 (a) H. Ephardt and P. Fromherz, J. Phys. Chem., 1989, 93, 7717;
(
(
b) H. Ephardt and P. Fromherz, J. Phys. Chem., 1991, 95, 6792;
c) P. Fromherz and A. Heilemann, J. Phys. Chem., 1992, 96, 6964.
28 W. G. Herkstroeter, J. Am. Chem. Soc., 1975, 97, 3090.
29 W. F. Smith, W. G. Herkstroeter and K. L. Eddy, J. Am. Chem. Soc.,
2
tuted in the R position.
1
975, 97, 2764.
3
0 (a) R. S. Davidson and P. R. Steiner, J. Chem. Soc., Chem. Commun.,
1971, 1682; (b) R. S. Davidson, P. R. Harrison and P. R. Steiner,
J. Chem. Soc., Chem. Commun., 1971, 3480; (c) R. F. Bartholomew,
D. R. G. Brimage and R. S. Davidson, J. Chem. Soc., Chem.
Commun., 1971, 3482.
Acknowledgements
This research was sponsored by the State Committee for
Scientific Research (KBN), grant No. 3 TO9B 087 15, and (for
G. L. H.) by the office of Basic Energy Sciences of the US
Department of energy. This paper is Document No. NDRL
31 W. G. Herkstroeter, J. Am. Chem. Soc., 1976, 98, 6210.
3
3
2 D. Rehm and A. Weller, Isr. J. Chem., 1970, 8, 259.
3 G. Pandey, Photoinduced Electron Transfer (PET) in Organic
Synthesis, in Top. Curr. Chem., 1993, 168, 175.
4 Z. Kucybała and J. P a˛ czkowski, unpublished work. The mass spectra
and NMR data of the product formed during irradiation of the dye
in presence of N-phenylglycine indicate complex molecule
containing in its structure both the dye and N-phenylglycine moiety.
-
4100 from the Notre Dame Radiation Laboratory.
3
References
1
2
P. W. Vittum and A. J. Weissberger, J. Photogr. Sci., 1954, 2, 81.
G. Tacconi, G. Marinoni, P. P. Righetti and G. Desimoni, J. Prakt.
Chem., 1980, 322, 674.
35 R. A. Marcus, Annu. Rev. Phys. Chem., 1969, 15, 155.
3
4
Z. Kucybała and J. Gaca, J. Prakt. Chem., 1988, 330, 435.
W. F. Smith, W. G. Herkstoeter and K. L. Eddy, Photogr. Sci. Eng.,
1
976, 20, 140.
Paper 9/03363G
2
154
J. Chem. Soc., Perkin Trans. 2, 1999, 2147–2154