Keith A. Walters

Metal-to-ligand charge transfer absorption in a rhenium(I) complex that contains a π-conjugated bipyridine acceptor ligand

Abstract This Letter describes a study of the absorption and electroabsorption spectroscopy of a complex consisting of the –Re I (CO) 3 Cl chromophore coordinated to the 4,4 ′ -{bis-[2,5-(dimethoxyphenyl)ethynyl]}-2,2 ′ -bipyridine ligand. The objective of the study is to explore whether Re → bipyridine metal-to-ligand charge transfer (MLCT) excitation leads to electron delocalization into the π-conjugated 2,5-(dimethoxyphenyl)ethynylene moieties. The results indicate that the two low-energy absorption bands observed for the complex have a strong degree of charge transfer character; however, the bands are dominated by intraligand (IL) π,π * transitions. The spectroscopic data are consistent with possible configuration mixing between the lowest IL π,π * and MLCT transitions.

Photophysics of metal-organic π-conjugated oligomers and polymers

Abstract A series of phenylene-ethynylene based π-conjugated oligomers that contain a 2,2′-bipyridine metal chelating unit has been synthesized by using Pd-mediated coupling chemistry. The photophysics of the free oligomers and complexes of the oligomers with the Re 1 (CO) x Cl metal chromophore is reported. These oligomers serve as excellent models for π-conjugated metal-organic polymers.

Photophysics of π-conjugated metal-organic oligomers*

The optical absorption and photoluminescence properties of PPE-type p-conjugated oligomers that contain a 2,2-bipyridine-5,5¢-diyl metal coordinating unit have been examined. The spectra of the free oligomers are compared with those that contain Re(CO)3Cl and Ru(bpy)22+ chromophores chelated to the bpy-diyl unit.

Study of the Heterocyclic-Substituted Platinum-1,2-Enedithiolate 3ILCT Excited States by Transient Absorption Spectroscopy

The photoluminescent 1,2-enedithiolate complexes, (dppe)Pt{S2C2(2-quinoxaline)(H)}, [L2Pt{S2C2(2-pyridinium)(H)}]+ where L2 = dppm and dppe, [L2Pt{S2C2(4-pyridinium)(H)}]+, [L2Pt{2C2(N-Methyl-4-pyridinium)(H)}]+ and [L2Pt{S2C2(CH2CH2-N-2-pyridinium)}]+ where L2 = dppm, dppe, and dppp are room temperature dual emitters where the emissions have thiolate to heterocycle π* intraligand charge transfer character (ILCT) singlet and triplet character. The pyridinium complexes have strong triplet-triplet absorption bands at approximately 400, 520 and 630 nm with a weaker band at 800 nm while (dppe)Pt{S2C2(2-quinoxaline)(H)} has strong triplet-triplet absorption bands at 385 and 550 nm with weaker bands at 610 and 805 nm. By fitting the decay of the transients to single exponential kinetics, the 3ILCT* lifetimes of the pyridinium complexes where determined to be 0.7 to 15.9 μs (DMSO) while the 3ILCT* lifetime of (dppe)Pt{S2C2(2-quinoxaline)(H)} was determined to be 2.8 μs (CH3CN). The transient absorption spectra of the complexes is affected by the appended heterocycle rather than the bulk of ancillary phosphine ligand or whether the heterocycle is protonated or alkylated.

Triplet state photophysics in an aryleneethynylene π-conjugated polymer

The triplet state photophysics of a polyaryleneethynylene π-conjugated polymer and a related model compound are investigated with various techniques, including laser flash photolysis and time-resolved thermal lensing (TRTL).

Synthesis and Preliminary Characterization of a PPE-Type Polymer Containing Substituted Fullerenes and Transition Metal Ligation Sites

A substituted fullerene was incorporated into a PPE-conjugated polymer repeat unit. This subunit was then polymerized via Sonogashira coupling with other repeat units to create polymeric systems approaching 50 repeat units (based on GPC characterization). Bipyridine ligands were incorporated into some of these repeat units to provide sites for transition metal coordination. Photophysical characterization of the absorption and emission properties of these systems shows excited states located on both the fullerene and aromatic backbone of the polymers that exist in a thermally controlled equilibrium. Future work will explore other substituted polyaromatic systems using similar methodologies.