Emission Tuning of Ir(N^∧C)₂(pic)-Based Complexes via Torsional Twisting of Picolinate Substituents

Pyridine-2-carboxylate (pic) has been employed extensively as a blue-shifting ancillary ligand in the production of cyclometalated iridium complexes used in OLEDs, but surprisingly, further elaboration of this ligand has largely been unexplored. In this work we demonstrate a simple and versatile route for modifying picolinate ligands coordinated to iridium. Reacting a μ-chloro iridium­(C^∧N) dimer (where C^∧N is a phenylpyridine-based ligand) with 4-bromopicolinic acid (HpicBr) yields the corresponding iridium­(C^∧N)₂(picBr) complexes, which were readily modified by a Suzuki–Miyaura reaction to give the corresponding aryl-substituted picolinate complexes. The luminescent behavior of these complexes shows that by restricting the torsional angle between the substituent and pic the emission can be shifted by up to 77 nm

Single-Molecule Conductance Behavior of Molecular Bundles

Controlling the orientation of complex molecules in molecular junctions is crucial to their development into functional devices. To date, this has been achieved through the use of multipodal compounds (i.e., containing more than two anchoring groups), resulting in the formation of tri/tetrapodal compounds. While such compounds have greatly improved orientation control, this comes at the cost of lower surface coverage. In this study, we examine an alternative approach for generating multimodal compounds by binding multiple independent molecular wires together through metal coordination to form a molecular bundle. This was achieved by coordinating iron(II) and cobalt(II) to 5,5′-bis(methylthio)-2,2′-bipyridine (L1) and (methylenebis(4,1-phenylene))bis(1-(5-(methylthio)pyridin-2-yl)methanimine) (L2) to give two monometallic complexes, Fe-1 and Co-1, and two bimetallic helicates, Fe-2 and Co-2. Using XPS, all of the complexes were shown to bind to a gold surface in a fac fashion through three thiomethyl groups. Using single-molecule conductance and DFT calculations, each of the ligands was shown to conduct as an independent wire with no impact from the rest of the complex. These results suggest that this is a useful approach for controlling the geometry of junction formation without altering the conductance behavior of the individual molecular wires

Toward an Iron(II) Spin-Crossover Grafted Phosphazene Polymer

Two new cyclotriphosphazene ligands with pendant 2,2′:6′,2″-terpyridine (Terpy) moieties, namely, (pentaphenoxy)­{4-[2,6-bis­(2-pyridyl)]­pyridoxy}­cyclotriphosphazene (<b>L¹</b>), (pentaphenoxy)­{4-[2,6-terpyridin-4-yl]­phenoxy}­cyclotriphosphazene (<b>L²</b>), and their respective polymeric analogues, <b>L^1P</b> and <b>L^2P</b>, were synthesized. These ligands were used to form iron­(II) complexes with an Fe^IITerpy₂ core. Variable-temperature resonance Raman, UV–visible, and Mössbauer spectroscopies with magnetic measurements aided by density functional theory calculations were used to understand the physical characteristics of the complexes. By a comparison of measurements, the polymers were shown to behave in the same way as the cyclotriphosphazene analogues. The results showed that spin crossover (SCO) can be induced to start at high temperatures by extending the spacer length of the ligand to that in <b>L²</b> and <b>L^2P</b>; this combination provides a route to forming a malleable SCO material

Toward an Iron(II) Spin-Crossover Grafted Phosphazene Polymer

Two new cyclotriphosphazene ligands with pendant 2,2′:6′,2″-terpyridine (Terpy) moieties, namely, (pentaphenoxy)­{4-[2,6-bis­(2-pyridyl)]­pyridoxy}­cyclotriphosphazene (<b>L¹</b>), (pentaphenoxy)­{4-[2,6-terpyridin-4-yl]­phenoxy}­cyclotriphosphazene (<b>L²</b>), and their respective polymeric analogues, <b>L^1P</b> and <b>L^2P</b>, were synthesized. These ligands were used to form iron­(II) complexes with an Fe^IITerpy₂ core. Variable-temperature resonance Raman, UV–visible, and Mössbauer spectroscopies with magnetic measurements aided by density functional theory calculations were used to understand the physical characteristics of the complexes. By a comparison of measurements, the polymers were shown to behave in the same way as the cyclotriphosphazene analogues. The results showed that spin crossover (SCO) can be induced to start at high temperatures by extending the spacer length of the ligand to that in <b>L²</b> and <b>L^2P</b>; this combination provides a route to forming a malleable SCO material