Radical Ion States of Platinum Acetylide Oligomers

Abstract

The ion radicals of two series of platinum acetylide oligomers have been subjected to study by electrochemical and pulse radiolysis/transient absorption methods. One series of oligomers, Ptn, has the general structure Ph-C[triple bond]C-[Pt(PBu3)2-C[triple bond]C-(1,4-Ph)-C[triple bond]C-]n-Pt(PBu3)2-C[triple bond]C-Ph (where x=0-4, Ph=phenyl and 1,4-Ph=1,4-phenylene). The second series of oligomers, Pt4Tn, contain a thiophene oligomer core, -C[triple bond]C-(2,5-Th)n-C[triple bond]C- (where n=1-3 and 2,5-Th=2,5-thienylene), capped on both ends with -Pt(PBu3)2-C[triple bond]C-(1,4-Ph)-C[triple bond]C-Pt(PBu3)2-C[triple bond]C-Ph segments. Electrochemical studies reveal that all of the oligomers feature reversible or quasi-reversible one-electron oxidation at potentials less than 1 V versus SCE. These oxidations are assigned to the formation of radical cations on the platinum acetylide chains. For the longer oligomers multiple, reversible one-electron waves are observed at potentials less than 1 V, indicating that multiple positive polarons can be produced on the oligomers. Pulse-radiolysis/transient absorption spectroscopy has been used to study the spectra and dynamics of the cation and anion radical states of the oligomers in dichloroethane and tetrahydrofuran solutions, respectively. All of the ion radicals exhibit two allowed absorption bands: one in the visible region and the second in the near-infrared region. The ion radical spectra shift with oligomer length, suggesting that the polarons are delocalized to some extent on the platinum acetylide chains. Analysis of the electrochemical and pulse radiolysis data combined with the density functional theory calculations on model ion radicals provides insight into the electronic structure of the positive and negative ion radical states of the oligomers. A key conclusion of the work is that the polaron states are concentrated on relatively short oligomer segments.

Bichromophoric Compounds with Orthogonally and Parallelly Arranged Chromophores Separated by Rigid Spacers

“…(2) Regioselective iodination of bithiophene derivative 1 was carried out under conditions given in ref. [10] .…”

Expanding iClick to group 9 metals

“…Preparing metallopolymers requires either appending metal ions to an already existing polymer backbone or incorporating them into the repeating unit directly . Conjugated platinum(II) acetylide oligomers/polymers, studied extensively by Schanze and co-workers [33][34][35][36][37][38][39][40], are hallmark examples of incorporating metal ions into the propagating repeat unit. The platinum ions engender photophysical properties that are challenging or impossible to replicate by organic polymers alone.…”

Photoinduced Charge Separation in Platinum Acetylide Oligomers

“…19 Studies of the polaron states (cation and anion radicals) show that the charged states are spatially confined, much like the triplet state. 20 Given these results, it can be expected that the platinum acetylide system could serve as a spacer supporting charge separation; however, the existence of energetically accessible hole and electron states may facilitate electron (or hole) transport over relatively long distances.…”