A Platinum Acetylide Polymer with Sterically Demanding Substituents: Effect of Aggregation on the Triplet Excited State

The effect of interchain interaction on the triplet excited state is explored in two Pt−acetylide polymers of the type
[−trans-Pt(PBu3)2−C⋮C−Ar−C⋮C−]n, where Ar is either 1,4-phenylene or is based on the pentiptycene unit
(polymers 2 and 3, respectively). To explore the effect of interchain interaction in Pt−acetylide materials, the optical
properties of parent polymer 2 are compared with those of polymer 3 in which interchain interaction is precluded
by the sterically bulky pentiptycene moiety. Insight into the effect of the pentiptycene unit on packing in the solid
state comes from the X-ray structure of monomer 1b, Ph−C⋮C−[trans-Pt(PBu3)2]−C⋮C−Ar−C⋮C−[trans-Pt(PBu3)2]−C⋮C−Ph. Spectroscopic studies indicate that weak phosphorescence emission from an interchain aggregate is
observed from parent polymer 2, both in solution and in the solid state. By contrast, the photophysics of 3 is
dominated by the intrachain triplet exciton. Interestingly, the phosphorescence emission of polymer 3 in the solid
state is nearly superimposable with that of a single crystal of monomer 1b, suggesting that the solid polymer
experiences an environment that is similar to that of the monomer in the crystal.