Modulation of the ligational properties of a new cylindrical macrotricycle by coupling of photochemical- and pH-switching properties

Abstract

The new cylindrical molecule L containing two tetraazamacrocyclic rings linked by two azobenzene pillars displays photoelastic properties. Light absorption at 366 nm gives rise to trans → cis isomerization of the azobenzene moieties producing two isomers containing one or two cis-azobenzenes, respectively. The three trans-trans (E-E), trans-cis (E-Z) and cis-cis (Z-Z) isomers have been identified and characterized by ¹H NMR spectroscopy, allowing the dependence of their formation percentages with irradiation time to be determined. The sequence of photochemical reactions E-E → E-Z → Z-Z allows almost complete conversion of the E-E into the Z-Z isomer at 366 nm and 298 K. Both thermal (k = 1.75 × 10^–5 s^–1 at 313 K) and photo-induced (at 436 and 313 nm) back-isomerization reactions have been studied. The protonation constants of the three isomers in equimolar solutions of water–DMSO indicate a decreasing basicity in the order E-E > E-Z > Z-Z, in agreement with increasing electrostatic repulsion between the positive charges caused by a reduction in the separation between the protonation sites occurring upon Z → E isomerization.

References

1. H. Rau, in Photochromism Molecules and Systems, eds. H. Dürr and H. Bouas-Laurent, Elsevier, Oxford, 1990, ch. 4.
2. V. Balzani and F. Scandola, Supramolecular Photochemistry, Ellis Horwood, Chichester, 1991, ch. 7.
3. (a) S. Shinkai, T. Nakaji, Y. Nishida and T. Ogawa, J. Am. Chem. Soc., 1980, 102, 5860; (b) S. Shinkai, T. Kounot, Y. Kusano and O. Manabe, J. Chem. Soc., Perkin Trans. 2, 1982, 2741.
4. H. W. Losensky, H. Spelthann, A. Elhen, F. Vögtle and J. Bargon, Angew Chem., Int. Ed. Engl., 1988, 27, 1189.
5. K. Ueno, H. Yoshimura, R. Saka and T. Osa, J. Am. Chem. Soc., 1979, 101, 2729.
6. K. Ueno, R. Saka and T. Osa, Chem. Lett., 1979, 841.
7. S. Shinkai and O. Manabe, Top. Curr. Chem., 1984, 121, 67.
8. S. Shinkai, Y. Honda, Y. Kusano and O. Manabe, J. Chem. Soc., Chem. Commun., 1982, 848; S. Shinkai, Y. Honda, T. Minami, K. Ueda, O. Manabe and M. Tashiro, Bull. Chem. Soc. Jpn., 1983, 56, 1700; S. Shinkai, Y. Honda, K. Ueda and O. Manabe, Israel. J. Chem., 1984, 24, 302.
9. M. Shiga, M. Takagi and K. Ueno, Chem. Lett., 1990, 1021.
10. S. Shinkai, T. Ogawa, T. Nakaji and O. Manabe, J. Chem. Soc., Chem. Commun., 1980, 375.
11. S. Shinkai, T. Nakaji, T. Ogawa, K. Shigematsu and O. Manabe, J. Am. Chem. Soc., 1981, 103, 111.
12. S. Shinkai, T. Ogawa, Y. Kusano, O. Manabe and K. Kikukaw, J. Am. Chem. Soc., 1979, 101, 1334.
13. A. Bianchi, M. Micheloni and P. Paoletti, Coord. Chem. Rev., 1991, 110, 17.
14. R. M. Izatt, K. Pawlak, J. S. Bradshaw and R. L. Bruening, Chem. Rev., 1995, 33, 2529.
15. Supramolecular Chemistry of Anions, eds. A. Bianchi, K. Bowman-James and E. Garcia-España, VCH-Wiley, New York, 1997.
16. P. Bortolus and S. Monti, J. Phys. Chem., 1979, 83, 648.
17. M. Ciampolini, P. Dapporto, M. Micheloni, N. Nardi, P. Paoletti and F. Zanobini, J. Chem. Soc., Dalton Trans., 1984, 1357.
18. C. G. Hatchard and C. A. Parker, Proc. R. Soc. London, Ser. A, 1956, 235, 518.
19. A. Bianchi, L. Bologni, P. Dapporto, M. Micheloni and P. Paoletti, Inorg. Chem., 1984, 23, 1201.
20. G. Gran, Analyst (London), 1952, 77, 661; F. J. Rossotti and H. Rossotti, J. Chem. Educ., 1965, 42, 375.
21. P. Gans, A. Sabatini and A. Vacca, Talanta, 1996, 43, 1739.