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

摘要

Dinuclear acetylide-type complexes bridged by a photochromic dithienylethene unit (DTE), [YCCDTECCY] 1 (Y={MCp*(dppe)}; Cp*=pentamethylcyclopentadienyl, M=Fe (1Fe), Ru (1Ru)), 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 1Ru is superior to the iron analogue 1Fe. The wirelike performance is associated with the photochromic processes, and the efficient switching performance has been verified for 1Fe as characterized by the V_ab values [V_ab is the electronic coupling derived from intervalence charge-transfer (IVCT) bands: V_ab(1FeC; ON)=0.047 eV versus V_ab(1FeO; 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 1Ru is determined to be 4.2. The remarkable switching behavior arises from the different π-conjugated systems in the two isomeric forms, that is, cross-conjugated (1O) and fully conjugated π-systems (1C). It was also found that, in contrast to the reversible redox behavior of the iron complex 1Fe, the ruthenium complex 1RuO undergoes oxidative ring closure to form the dicationic species of the closed isomer 1RuC2+ and, thus, the ruthenium system 1Ru shows dual photo- and electrochromism. The distinct oxidation behavior of 1Fe and 1Ru can be ascribed to the spin distribution on the diradical intermediates 1FeO2+ and 1RuO2+, as supported by DFT calculations.