Synthesis, Characterization, and Photochemical Properties of Azobenzene-Conjugated Ru(II) and Rh(III) Bis(Terpyridine) Complexes

Abstract

We synthesized azobenzene-conjugated bis(terpyridine) Ru(II) and Rh(III) mononuclear and dinuclear complexes and investigated their photochemical properties on excitation of the azo pi-pi band upon 366 nm light irradiation. The Ru mononuclear complex underwent trans-to-cis photoisomerization to reach the photostationary state with only 20% of the cis form, while the Ru dinuclear complex did not isomerize at all photochemically. On the other hand, the mononuclear and dinuclear Rh complexes showed almost complete trans-to-cis photoisomerization behavior. Cis forms of the Rh complexes thermally returned to the trans form at a much slower rate than those of organic azobenzenes, but they did not isomerize photochemically. The reduction potential of the cis forms was 80 mV more negative than that of the trans forms. The photoisomerization quantum yields of the Rh complexes were strongly dependent on the polarity, viscosity, and donor site of the solvents as well as the size of the counterions. We investigated the photoisomerization process of these complexes using femtosecond absorption spectroscopy. For the Rh complexes, we observed S(n) <-- S(2) and S(n) <-- S(1) absorption bands similar to those of organic azobenzenes. For the Ru complexes, we observed very fast bleaching of the MLCT band of the Ru complex, which indicated that the energy transfer pathway to the MLCT was the primary cause of the depressed photoisomerization. The electronic structures, which were estimated from ZINDO molecular orbital calculation, supported the different photochemical reaction behavior between the Ru and Rh complexes.

Near-Infrared Photoluminescence and Reversible Trans-to-Cis Photoisomerization of Mononuclear and Binuclear Ytterbium(III) Complexes Functionalized by Azobenzene Groups

“…At 50 °C, the first-order rate constants for cis-to-trans thermal isomerization of H 2 DL, [Yb(tfd) 2 L], and [Yb 2 (tfd) 4 (DL)] in solution are similar to those of similar azobenzene-containing lanthanide complexes and higher than those of other azobenzene-containing metal complexes. 41,42…”

Crystal structure of bis-(5-bromo-2-methyl-phenyl)-diazene, C14H12Br2N2

“…For the high coordination numbers, along with special magnetic elements for constructing CPs has attracted a lot of interest [4]. Designing solids with molecules that encode well defined non-covalent interactions has recently become a rapidly growing area of research due to their fascinating molecular and supramolecular structural diversity and potential applications for catalysis [5] and material sciences [6][7][8][9]. Substituted aromatic azo compounds are also important units in the area of nonlinear optics, optical storage media, chemo sensors, photochemical switches and electronic devices.…”

Induction of E/Z isomerization in a pendant metal-bound azobenzene: a synthetic, spectroscopic and theoretical study

“…[1][2][3][4] Azobenzene has been appended to a number of chromophores, including transition metal complexes, in an attempt to couple the E/Z isomerization process to an external electronic transition. [5][6][7][8][9][10][11][12][13] Transition metal compounds that exhibit metal to ligand charge transfer transitions (MLCT), as seen in many d 6 metal complexes, are ideal for transferring energy to an external group. [14][15][16][17][18] In this report, we present a study of two Re(CO) 3 diimine complexes with a pendant azobenzene group.…”