A Future Perspective on Phototriggered Isomerizations of Transition Metal Sulfoxides and Related Complexes

Abstract

Photochromic molecules are examples of light-activated bistable molecules. We highlight the design criteria for a class of ruthenium and osmium sulfoxide complexes that undergo phototriggered isomerization of the bound sulfoxide. The mode of action in these complexes is an excited-state isomerization of the sulfoxide from S-bonded to O-bonded. We discuss the basic mechanism for this transformation and highlight specific examples that demonstrate the effectiveness and efficiency of the isomerization. We subsequently discuss future research directions within the field of phototriggered sulfoxide isomerizations on transition metal polypyridine complexes. These efforts involve new synthetic directions, including the choice of metal as well as new ambidentate ligands for isomerization.

Cobalt(III) Carbene Complex with an Electronic Excited-State Structure Similar to Cyclometalated Iridium(III) Compounds

“… 57 , 156 Even well-known MLCT emitters such as [Ru(bpy) 3 ] 2+ and related 4d 6 /5d 6 luminophores undergo rather facile photodegradation, 129 , 157 typically as a result of the thermal population of MC states with metal–ligand dissociative character. 17 , 158 − 160 Against this background, it seemed interesting to test the inherent photostability of [Co(L CNC ) 2 ](PF 6 ) under continuous photoirradiation.…”

Luminescent First-Row Transition Metal Complexes

“…On the one hand, this includes comparatively abundant second- and third-row transition metals (for example Zr, , Mo, ,,, or W ,,,, ) or f-elements (for example Ce , ). On the other hand, molecular complexes of abundant main group elements are now attracting increasing attention as luminophores and provide additional insight into how nonradiative relaxation can be tamed. − At the same time, further developments of precious metal-based complexes (for example, Ru, ,, Rh, , Re, − Ir, − or Pt − ) have significantly advanced the field of inorganic photophysics and photochemistry. Regardless of whether complexes of d-, f-, or main group elements are considered, the interplay between synthetic, spectroscopic, and computational work seems crucial for the development of new designer luminophores.…”

Slow 3MLCT Formation Prior to Isomerization in Ruthenium Carbene Sulfoxide Complexes

“…These absorption maxima are in accord with the photoproduct absorption maxima reported here of 493 nm (RuOTE3), 490 nm (RuOTE3), and 474 nm (RuOTE9). On the basis of this report and other examples of sulfoxide isomerization on ruthenium bipyridine centers, we propose that the photoproduct formed upon irradiation is the O-bonded isomer. − ,− …”

“…Irradiation of RuOTE3, RuOTE4, or RuOTE9 in an acetonitrile, alcohol, halogenated, or propylene carbonate solution yields dramatic changes in the absorption spectrum that are consistent with previous reports of sulfoxide isomerization on ruthenium. − Shown in Figure a are representative spectra of RuOTE9 of the photochemical transformation from the S-bonded isomer to the proposed O-bonded isomer. We find few complexes in the literature that have a similar coordination sphere for comparison, but we note that Tennyson and co-workers report an absorption maximum of 496 nm for a [Ru­(bpy) 2 ] 2+ center with a chelating benzimidazolylidene carboxylate (C, O coordination mode) .…”

“…There are many classes of photochromic compounds such as azobenzenes, − Stenhouse adducts, , dithienylethenes, − and azoaryltriazoles, , to name just a few. Our group has focused on ruthenium and osmium sulfoxide compounds, − which comprise a group of transition metal-based complexes that show photochromic behavior based on ligand isomerization. − Typically, these sulfoxide complexes feature an S-bonded lowest-energy isomer and an O-bonded metastable isomer along the ground state potential energy surface. In an overly simplistic but useful model, these compounds may be analyzed by a four-energy level diagram (Scheme ).…”