Issue 2, 1998

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.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1998, 413-418

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

A. Bencini, M. Alexandra Bernardo, A. Bianchi, M. Ciampolini, V. Fusi, N. Nardi, A. Jorge Parola, F. Pina and B. Valtancoli, J. Chem. Soc., Perkin Trans. 2, 1998, 413 DOI: 10.1039/A704096B

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