5
6
7
J. S. Connolly, Photochemical Conversion and Storage of Solar
Energy, Academic Press, New York, 1981.
A. Slama-Schwok, D. Avnir and M. Ottolenghi, Photochem. Pho-
tobiol., 1991, 54, 525.
D. Gust, T. A. Moore, P. A. Liddell, G. A. Nemeth, L. R.
Makings, A. L. Moore, D. Barrett, P. J. Pessiki, R. V. Bensasson,
M. Rougee, C. Chachuty, F. C. De Schryver, M. van der
Auweraer, A. R. Holzwarth and J. S. Connolly, J. Am. Chem.
Soc., 1987, 109, 846.
P. D. Dutta and J. A. Incavo, J. Phys. Chem., 1987, 91, 4443.
T. J. Meyer, Acc. Chem. Res., 1989, 22, 163.
T. Nakato, K. Kazuyuki and C. Koto, Chem. Mater., 1992, 4,
128.
photoyield. The photoyield and stability of PC` cation rad-
n
icals in ZrP1PC prepared by either impregnation or ion-
n
exchange are similar. Therefore, both impregnation and
ion-exchange seem equally good for incorporating PC mol-
n
ecules onto ZrP for efficient photooxidation.
The relative mobilities of the PC` cation radicals are
n
revealed by the partially resolved ESR spectra in Fig. 2. The
results suggest a greater mobility for PC` with smaller alkyl
n
8
9
0
chain lengths which correlates with greater probability for
decay by back electron transfer from ZrP or by some other
1
process (Figs. 9È11). The lifetimes of the PC` cation radicals
n
in ZrP range from a few days to several weeks at room tem-
11 A. Slama-Schwok, M. Ottolenghi and D. Avnir, Nature, 1992,
55, 40.
W. F. Forbes and P. D. Sullivan, J. Am. Chem. Soc., 1966, 88,
862.
3
perature, depending on the alkyl chain length of the PC`
n
1
2
3
cation radicals (Figs. 9È11).
2
The results obtained here for the photoionization of N-
alkylphenothiazines in ZrP with longer alkyl chain lengths are
di†erent from previous work on the photooxidation of N-
alkylphenothiazines with longer alkyl chain lengths in silica
gels.17 As a function of alkyl chain length in ZrP, the photo-
yield increases nearly threefold when compared to silica gel.17
1
H. J. Shine, D. R. Thompson and C. Veneziani, J. Heterocycl.
Chem., 1967, 4, 517.
14 E. R. Biehl, H. S. Chiou, J. Keepers, S. Kennard and P. C. Reeves,
J. Heterocycl. Chem., 1975, 12, 397.
1
1
1
5
6
7
D. Clarke, B. C. Gilbert and P. Hanson, J. Chem. Soc., Perkin
T rans., 1978, 2, 1103.
S. A. Alkaitis, G. Beck and M. Gratzel, J. Am. Chem. Soc., 1975,
97, 5723.
Also, the stability of PC` cation radicals is higher (from days
n
to several weeks) in ZrP at room temperature as compared to
B. Xiang and L. Kevan, L angmuir, 1994, 10, 2688.
silica gel where the PC` cation radicals are stable only for a
18 M. Sakaguchi, M. Hu and L. Kevan, J. Phys. Chem., 1990, 94,
n
few hours at room temperature. This suggests that the photo-
870.
1
2
9
0
M. Hu and L. Kevan, J. Phys. Chem., 1990, 94, 5348.
Y. S. Kang, P. Baglioni, H. J. D. McManus and L. Kevan, J.
Phys. Chem., 1990, 94, 870.
oxidation mechanism of PC` cation radicals in ZrP is more
n
efficient than in silica gel for similar molecules.
21
22
23
Y. S. Kang, H. J. D. McManus and L. Kevan, J. Phys. Chem.,
1
993, 97, 2027.
Conclusions
Inorganic Ion Exchange Materials, ed. A. ClearÐeld, CRC, Boca
Raton, FL, 1982.
The e†ect of the alkyl chain length on the photooxidation
yield of a series of N-alkylphenothiazine molecules in ZrP was
determined by ESR and di†use reÑectance spectroscopy. The
S. B. Ungashe, W. L. Wilson, H. E. Katz, G. R. Scheller and T.
M. Putrvinski, J. Am. Chem. Soc., 1992, 114, 8717.
A. ClearÐeld and G. D. Smith, Inorg. Chem., 1969, 8, 431.
R. C. Yeates, S. T. Kuznicki, L. B. Lloyd and E. M. Eyring, J.
Inorg. Nucl. Chem., 1981, 43, 2355.
2
2
4
5
photoyield and stability of the PC` cation radicals depends
n
strongly on the pendent alkyl chain length. The highest photo-
yield is obtained for ZrP1PC` whereas the maximum radical
26 A. ClearÐeld and J. A. Stynes, J. Inorg. Nucl. Chem., 1964, 26,
17.
27 I. Gozlan, D. Ladkani, M. Halpern, M. Rabinovitz and D. J.
6
1
1
stability is found for ZrP1PC` . The photoyield and stability
6
also depend upon the mobility of the alkylphenothiazine
cation radicals. Impregnation and ion-exchange methods are
equally good for incorporating alkylphenothiazine molecules
onto ZrP for efficient photooxidation. By both impregnation
or ion-exchange, the N-alkylphenothiazine molecules are
adsorbed only on the external surface of ZrP. These results
clearly highlight the utility of a-ZrP in controlling the photo-
Anoir, J. Heterocycl. Chem., 1984, 21, 613.
2
8 S. A. Alkaits, G. Beck and M. Gratzel, J. Am. Chem. Soc., 1975,
97, 5723.
29 M. C. Hovey, J. Am. Chem. Soc., 1982, 104, 4196.
30 H. Hase and L. Kevan, J. Phys. Chem., 1970, 94, 3355.
3
1
A. M. Braun, M.-A. Gilson, M. Krieg, M.-T. Maurett, P. Mura-
secco and E. Oliveros, in Organic Phototransformations in Non-
homogeneous Media, ACS Symp. Ser. 278, ed. M. A. Fox.
American Chemical Society, Washington, DC, 1985, p. 79.
N. I. Wakayama, Bull. Chem. Soc. Jpn., 1971, 44, 2847.
P. Kabasakalian and J. MacGlotten, Anal. Chem., 1959, 31, 431.
C. Bodea and I. Silberg, Advn. Heterocycl. Chem., 1968, 9, 321.
B. Xiang and L. Kevan, L angmuir, 1995, 11, 860.
L. S. Levitt and H. F. Widing, in Progress in Physical Organic
Chemistry, ed. R. W. Taft, Wiley, New York, 1976, vol. 12, ch. 5.
process of PC molecules.
n
32
33
34
35
36
Acknowledgements
This research work was supported by the Division of Chemi-
cal Sciences, Office of Basic Energy Sciences, Office of Energy
Research, US Department of Energy and by the Texas
Advanced Research Program.
37 R. R. Gupta and K. Mahendra, in Phenothiazines and 1,4-Benzo-
thiazines: Chemical and Biomedical Aspects, ed. R. R. Gupta,
Elsevier, Amsterdam, 1988.
3
8
L. Louis, T. N. Tozer, L. D. Tuck and D. B. Loveland, J. Med.
References
Chem., 1972, 15, 898.
3
9
A. Ortiz and I. Poyato and J. I. Fernandez-Alonso, J. Pharm. Sci.,
1
Photoinduced Electron T ransfer, ed. M. A. Fox and M. Chanon,
Elsevier, Amsterdam, 1988.
1
983, 72, 50.
4
4
0
1
E. Pelizzetti and E. Mentasi, Inorg. Chem., 1979, 18, 583.
R. van Grondelle, Biochim. Biophys. Acta, 1985, 811, 147.
2
M. Gratzel, Heterogeneous Photochemical Electron T ransfer,
CRC, Boca Raton, FL, 1989.
3
4
J. H. Fendler, J. Phys. Chem., 1985, 89, 2730.
G. J. Kavarnos and N. J. Turro, Chem. Rev., 1986, 86, 401.
Paper 9/01801H
Phys. Chem. Chem. Phys., 1999, 1, 2833È2839
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