Platinum(II) Diimine Diacetylides:  Metallacyclization Enhances Photophysical Properties

Abstract

The synthesis, structural characterization, and photoluminescence properties of a new platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2'-diacetylide (tda), Pt(dbbpy)(tda) [dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine], are described. In CH2Cl2, Pt(dbbpy)(tda) exhibits a strong visible charge-transfer absorption and broad emission centered at 562 nm. The photoluminescence quantum yield and excited-state lifetime are 0.52 and 2.56 mus, respectively, at room temperature. These parameters indicate that the planarization and rigidity introduced by the cyclic diacetylide leads to a lower-energy-absorbing species displaying enhanced photophysics relative to the analogous Pt(dbbpy)(CCPh)2. Time-dependent density functional theory calculations, which include solvation by CH2Cl2 via the polarizable continuum model, are used to reveal the nature of the excited states in these molecules that are responsible for the charge-transfer transitions. The 77 K emission spectra of the two compounds in EtOH/MeOH glasses are compared, uncovering tda-based ligand-localized phosphorescence in the title compound.

Directly Coupled Versus Spectator Linkers on Diimine PtII Acetylides—Change the Structure, Keep the Function?

“…This blueshift in the absorption maximum is consistent with a metal‐to‐ligand/ligand‐to‐ligand charge‐transfer (ML/LL′CT) transition with significant involvement of the bipy π system in the LUMO . The methylene spacer decreases the electron‐withdrawing effect of the carboxyl/phosphonic ester group, and thus destabilises the LUMO and increases the HOMO–LUMO energy gap and consequently the energy of the corresponding absorption band.…”

“…All complexes displayed an electrochemically irreversible oxidation process between 0.67 and 0.73 V, attributed to the oxidation of the platinum acetylide subunit. The position and irreversible nature of this oxidation process is typical for platinum bipy acetylide complexes of this type . Little variation in oxidation potential between the four complexes implies that, as expected, the bipy ligands have little involvement.…”

Sterically Hindered Luminescent PtII–Phosphite Complexes for Electroluminescent Devices

“…The electrochemical measurements indicated that the oxidation processes are irreversible between +1.25 and +1.52 V, which can be attributed to the oxidation of the metal core (Table 5). 19, 24, 25 Such irreversibility is typical of Pt II complexes due to solvent coordination to the metal center upon oxidation, followed by a rearrangement of the ligands,26 which might also account for the lower current involved in the oxidation wave as compared to the reduction process. Complexes 1 and 4 showed reversibility in the reduction for scan rates above 0.5 and 2 V s −1 , respectively, whereas complexes 3 and 6 gave irreversible reductions between −1.7 and −1.9 V. The reduction of compounds 2 and 5 fall outside of the electrochemical window of the solvent/electrolyte, suggesting more negative reduction potentials (higher lying LUMOs) 27.…”

Solvent‐Induced and Temperature‐Promoted Aggregation of Bipyridine Platinum(II) Triangular Metallacycles and Their Near‐Infrared Emissive Behaviors

“…Youngs and co‐workers reported the first dinuclear platinum metallacyclyne and its single‐crystal structure . Castellano and co‐workers investigated the photophysical properties of discrete platinum(II) metallacycles . The emergence of discrete triangular bipyridine platinum(II) metallacycles and the study of their structures and photophysical properties have provided insights for the investigation of their supramolecular self‐assembly properties utilizing the large planar metallacycles –,.…”

“…Castellano and co‐workers investigated the photophysical properties of discrete platinum(II) metallacycles . The emergence of discrete triangular bipyridine platinum(II) metallacycles and the study of their structures and photophysical properties have provided insights for the investigation of their supramolecular self‐assembly properties utilizing the large planar metallacycles –,. Herein, we report a series of alkynylbipyridine platinum(II) complexes ( 1 – 5 ) with different triangular metallacycles and alkyl/oligoether chains (Scheme ).…”