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

Abstract

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 L(a-d) (o,o) (a, D = H; b, D = OMe; c, D = NMe(2); d, D = NBu(2)) and/or the Lewis character of the metal ion center L(a-d)ZnX(2) (o,o) (L(a-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 L(d)ZnCl(2) 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.

Photochromic DTE-Substituted-1,3-di(2-pyridyl)benzene Platinum(II) Complexes: Photomodulation of Luminescence and Second-Order Nonlinear Optical Properties

“…This is also supported by the appearance of a blue coloration of the solution after the emission measurement upon photo-excitation at 440 nm, an irradiation wavelength which can efficiently trigger the ring-closing process, especially in very dilute conditions. 16 To confirm this proposal, we performed emission studies of PtDTE1 at the PSS (Figure S20). This leads to the same result, with a quantum yield  less than 1 % and a luminescence spectrum similar to that obtained by starting with PtDTE1(o).…”

“…16a By contrast, upon visible irradiation, the presence of a saturated linker induces a lower rate of photocyclization. 16 Monitoring the ring-closure reaction by 1 H NMR spectroscopy gives access to the percentage of conversion at the photostationary state (PSS). Figure 5 shows the 1 H NMR spectra of PtDTE1 before and after irradiation at 350 nm.…”

“…This behavior, reported as a DTE ring-closure sensitization, was previously demonstrated for DTE-based Pt(terpyridine)(alkynyl) complexes where the DTE is connected to the alkynyl ligand and explained as an intra-molecular triplet energy transfer from the 3 CT states of the complex to the 3 IL (Intra-Ligand) state localized on the open DTE. 16 In particular, a former study demonstrated that reducing the orbital overlap between the metal-based and open DTE states, by breaking the conjugated pathway, dramatically diminishes the efficiency of the metal-sensitized photocyclization reaction. 16b Curiously, in the present designs of PtDTE1 and PtDTE2, the efficiency of the energy transfer toward the photoactive 3 ILDTE appears to be quantitative irrespective of the nature of the linkage, though, as mentioned above the reaction rate is slower in PtDTE2.…”

Multifunctional Photonic Molecular Logic Gate Based On A Biphotochromic Dyad With Reduced Energy Transfer

“…to more sophisticated ones (e.g. [18][19][20] In the triad consisting of one DTE and two fulgimide (FG) groups,t he DTE closed form quenches the FG closed form. ), have been realized using moleculars ystems.…”

“…For example, in bis-DTE dyads (DTE = dithienylethene), after photocyclization of the first DTE group, the quantum yield of the second group decreasesb ya no rdero fm agnitude, because the closed DTE isomer formed at the first stage acts as aq uencher. [18][19][20] In the triad consisting of one DTE and two fulgimide (FG) groups,t he DTE closed form quenches the FG closed form. [21] FRET is widely used in scientific investigations andi nn umerous applications.…”