Effect of platinum on the photophysical properties of a series of phenyl-ethynyl oligomers

In this work we detail the photophysical properties of a series of butadiynes having the formula H-(C6H4-Ctriple bond]C)n-(Ctriple bond]C-C6H4)n-H, n=1-3 and ligands H-(C6H4-Ctriple bond]C)n-H, n=1-3 and compare these to previous work done on a complimentary series of platinum-containing complexes having the formula trans-Pt(PC4H9)3]2(Ctriple bond]-C6H4)n-H]2, n=1-3. We are interested in understanding the role of the platinum in the photophysical properties. We found that there is conjugation through the platinum in the singlet states, but the triplet states show more complex behavior. The T1 exciton, having metal-to-ligand charge-transfer character, is most likely confined to one ligand but the Tn exciton appears to have ligand-to-metal charge-transfer character. The platinum effect was largest when n=1. When n=2-3, the S0-S1,S1-S0,T1-S0, and T1-Tn spectral properties of the platinum complex are less influenced by the metal, becoming equivalent to those of the corresponding butadiynes. When n=1, platinum decreases the triplet state lifetime, but its effect diminishes as n increases to 2.