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Tunable double photochromism of a family of bis-DTE bipyridine ligands and their dipolar Zn complexes

L. Ordronneau, V. Aubert, R. Metivier, E. Ishow, J. Boixel, K. Nakatani, F. Ibersiene, D. Hammoutene, A. Boucekkine, H. Le Bozec and V. Guerchais Phys. Chem. Chem. Phys., 2012, 14, 8, 2599-2605

The photoinduced ring-closure/ring-opening reactions of a series of bis-dithienylethene derivatives, as free ligands and Zn(II)-complexes, are investigated by resorting to theoretical (time-dependent density functional theory) and kinetic analyses in solution. The originality of the system stems from the tunability of the photoreaction quantum yields and conversion yields as a function of the electronic structure. The latter could be varied by modifying the electron-donating character of the DTE-end substituents La-d (o,o) (a, D = H; b, D = OMe; c, D = NMe2; d, D = NBu2) and/or the Lewis character of the metal ion center La-dZnX2 (o,o) (La-c, X = OAc; L-d, X = Cl). The orbital description of the doubly-open form (o,o) and half-closed form (o,c) predicts that double closure to the form (c,c) would occur using UV irradiation. Photokinetic studies on the complete series demonstrate that photocyclization proceeds following a sequential ring closure mechanism. They clearly point out distinct quantum yields for the first and second ring closures, the latter being characterized by a significantly lower value. Dramatic decrease in both the quantum yields of the ring-closure and ring-opening processes is demonstrated for the complex (LZnCl2)-Zn-d exhibiting the strongest charge-transfer character in the series investigated. These studies show that this series of DTE derivatives provides an efficient strategy to tune the photochromic properties through the combination of the electron-donor and electron-acceptor (D-A) groups.

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Publication

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Paru le 7 décembre 2011

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doi 10.1039/c2cp23333a