Photophysical Characterization of a Series of Platinum(II)-Containing Phenyl−Ethynyl Oligomers

A comprehensive photophysical study has been carried out on a series of platinum(II)-containing phenyl−ethynyl oligomers. The compounds are composed of a platinum center attached to two tributylphosphine ligands and two ligands that vary the number of repeat phenyl−ethynyl units (−PhC⋮C−). The objective of this work is to understand the effects of increased conjugation and the influence of the platinum on the overall electronic structure of the molecule. This was done by utilizing steady-state absorption, steady-state emission, picosecond pump−probe, and nanosecond laser flash photolysis techniques. The effect of increased conjugation is a red shift of S0−S1 and T1−Tn and an increase in both the S0−S1 and T1−Tn molar extinction coefficients. The spin−orbit coupling effect of platinum on the ground and excited-state properties is reduced with increased conjugation length because the S0−S1 transition is more localized on the ligand. As the ligand becomes larger, it takes on more π−π* character and therefore is spatially further away from the platinum center.