Photochromic Organometallics with a Dithienylethene (DTE) Bridge, [YCCDTECCY] (Y={MCp*(dppe)}): Photoswitchable Molecular Wire (M=Fe) versus Dual Photo‐ and Electrochromism (M=Ru)

Abstract

Dinuclear acetylide-type complexes bridged by a photochromic dithienylethene unit (DTE), [Y-C[triple bond]C-DTE-C[triple bond]C-Y] 1 (Y={MCp*(dppe)}; Cp*=pentamethylcyclopentadienyl, M=Fe (1(Fe)), Ru (1(Ru))), have been prepared, and their wirelike and switching behavior, as well as their oxidation chemistry has been investigated. The DTE complexes 1 exhibit photochromic behavior in a manner similar to organic DTE derivatives; UV irradiation causes ring closure of the open isomer 1O to form the closed isomer 1C and visible-light irradiation of the resultant 1C causes reverse ring opening to regenerate 1O. But the performance is dependent on the metals. With respect to the interconversion rates and the 1C content at the photostationary state under UV irradiation, the ruthenium complex 1(Ru) is superior to the iron analogue 1(Fe). The wirelike performance is associated with the photochromic processes, and the efficient switching performance has been verified for 1(Fe) as characterized by the V(ab) values [V(ab) is the electronic coupling derived from intervalence charge-transfer (IVCT) bands: V(ab)(1(Fe)C; ON)=0.047 eV versus V(ab)(1(Fe)O; OFF)=0 eV], and are also supported by the large switching factor (SF=K(C)(C; ON)/K(C)(O; OFF)=39; K(C)=comproportionation constant). SF for 1(Ru) is determined to be 4.2. The remarkable switching behavior arises from the different pi-conjugated systems in the two isomeric forms, that is, cross-conjugated (1O) and fully conjugated pi-systems (1C). It was also found that, in contrast to the reversible redox behavior of the iron complex 1(Fe), the ruthenium complex 1(Ru)O undergoes oxidative ring closure to form the dicationic species of the closed isomer 1(Ru)C(2+) and, thus, the ruthenium system 1(Ru) shows dual photo- and electrochromism. The distinct oxidation behavior of 1(Fe) and 1(Ru) can be ascribed to the spin distribution on the diradical intermediates 1(Fe)O(2+) and 1(Ru)O(2+), as supported by DFT calculations.

Diarylethene-Containing Carbon-Rich Ruthenium Organometallics: Tuning of Electrochromism

“…Indeed, a closing reaction attributable to the same origin was observed for the related ruthenium species A with direct σ-bonds between the metals and the thiophene units of the DTE 45 or via acetylene 46 46 This is consistent with our results and with the usual larger ability for ruthenium complexes to accommodate the single electron on carbonrich ligands. Finally, an additional phenylethynyl unit prevents the electrochemical closing in the ruthenium species, 86 showing that longer bridges lead to "dilution" of the spins and act against closing.…”

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

“…The Ru II metal ion was selected in this strategy because its complexes are electro‐active at low potentials7b–i, 8 and may allow for the synthesis of original redox‐triggered NLO‐active,9a luminescent,9b,c and electrochromic9d switches. As reported in 2012,4a 2‐ethynyl‐[6]helicene 1 a (Scheme ) was readily obtained on the gram‐scale by using classic photocyclization reactions1 from appropriate olefins bearing para ‐ ethynyl‐substituents and was resolved by HPLC separation over a chiral stationary phase.…”

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

“…Oxidation of the ruthenium analogue [53-O] results in spontaneous ring-closing to yield [53-C] 2+ , which is similarly reduced to form neutral [53-C]. [192] In this instance the cumulenic dication [53-C] 2+ is so stable that the retro-conversion of [53-C] into [53-O] was not possible. In contrast, extension of the alkynyl-ruthenium path in complex 54 allows fully reversible electrochemical interconversion between the isomers.…”