Low-spin cobalt(ii) redox shuttle by isocyanide coordination

Abstract

The electron transfer kinetics in the DSSCs were tuned dramatically by coordination of the strong-field ligand 2,6-dimethyl isocyanide to induce a low-spin Co(ii) redox shuttle.

Metal Complex Molecular Solids Showing Band-like Transport Driven by In Situ Ligand Exchange

“…The maximum absorption peaks (λ max = 450−470 nm) can be attributed to the metal-to-ligand charge-transfer (MLCT) transition of [Cu(dmbpy) 2 ] + (Figures S16 and S17). In both the solutions and films, the MLCT peak intensities decrease gradually with an increasing amount of added TBP from 0 to 20 equiv of TBP but increase upon the addition of 40 Although the formal potential of [Cu(TBP) 4 ] 2+/+ is more negative than that of [Cu(dmbpy) 2 ] 2+/+ by 0.25 V, the electron transfer (for the oxidation of [Cu(dmbpy) 2 ] + ) occurs from [Cu(dmbpy) 2 ] + to [Cu(TBP) 4 ] 2+ , which results in a 74.2% oxidation yield (Figure S23). [Co(bpy) 3 ] 3+/2+ and [Co-(ppy) 2 ] 3+/2+ , which have more negative (by 0.41 V) and more positive (by 0.33 V) formal potentials than [Cu(dmbpy) 2 ] 2+/+ , respectively, show adequate absorbance changes and concomitant oxidation yields of [Cu(dmbpy) 2 ] + (5.6 and 80.7%, respectively; Figure S24).…”

“…To measure the conductivities of the liquid solutions and solid films of the metal complexes with TBP, we used sandwich structures with symmetric devices (PEDOT/electrolytes/PEDOT) for the liquid solutions and heterostructure devices (FTO/films/Au) for the solid films (Figure c,d). For symmetric cells of the liquid solutions, PEDOT films were coated on an FTO (TEC-7) electrode via electropolymerization . An aqueous solution of 0.01 M 3,4-ethylenedioxythiophene, 0.1 M lithium percolate, and 0.1 M sodium dodecyl sulfate was homogeneously dissolved with a tip ultrasonicator (Daigger Scientific) for 1 h (1 min on/off) in an ice bath and, subsequently, cooled to room temperature (25 °C).…”

Molecular Switch Cobalt Redox Shuttle with a Tunable Hexadentate Ligand

“…Large distortions from octahedral geometries have also been seen for the [Co(PY5Me 2 ) (CN)](OTf), [Co(PY5Me 2 DMP-CN)]-(PF 6 ) 2 , and [Co(ttcn)](BF 4 ) 2 complexes; however, these examples are all six-coordinate. 20,21,35 There are other examples of both five-coordinate and six-coordinate low-spin Co(II) complexes, and a cursory observation is that the ligand systems with more flexibility are typically six-coordinate due to their ability to accommodate the Jahn−Teller distortion. 36−39 One example utilizing a pentadentate thiocarbohydrazidebased ligand with four low-spin Co(II) metal centers demonstrates two six-coordinate metal centers and two fivecoordinate metal centers.…”

“…Detailed synthesis, characterization, and measurement details are in the Supporting Information. DSSC devices fabricated with LEG4 (3-{6-{4-[ bis (2′,4′-dibutyloxybiphenyl-4-yl)­amino-]­phenyl}-4,4-dihexyl-cyclopenta-[2,1- b :3,4- b ′]­dithiophene-2-yl}-2-cyanoacrylic acid) were fabricated following modified reported procedures . DSSC devices fabricated with AP25 + D35 were fabricated according to a modified report.…”

“…Our group has attempted to minimize the driving force by changing the spin state of cobalt redox shuttles by inducing low-spin Co­(II) complexes. By inducing a low-spin Co­(II) to low-spin Co­(III) electron-transfer process, the inner-sphere reorganization energy is decreased, reducing the necessary driving force for dye regeneration. , Two of the redox shuttles [Co­(ttcn)] 3+/2+ (ttcn itrithiacyclononane) and [Co­(PY5Me 2 ) (DMP-CN)] 3+/2+ [PY5Me 2 , is 2,6- bis (1,1- bis (2-pyridyl)-ethyl)­pyridine and DMP-CN is 2,6-dimethylphenyl isocyanide] showed efficient dye regeneration but still resided at redox potentials too positive for NIR sensitizers (Figure ). In addition, the performance of [Co­(ttcn)] 3+/2+ was limited by recombination, which we suggest can be improved via a combination of reducing the driving force for recombination, that is, pushing the potential negative, and increasing the reorganization energy.…”