Ketonic Defects in Ladder-type Poly(p-phenylene)s

We investigate the oxidative degradation process occurring in ladder-type poly(p-phenylene) (LPPP) by spectroscopic and quantum-chemical techniques. Annealing experiments carried out for two representatives of the class of LPPPʹs with different side chains relate the change in emissive behavior of the polymer to the presence of ketonic defects on the main chain. The geometry, excitation, and emission energies as well as vibrational modes are calculated for model LPPP oligomers bearing these defects. The optical properties of these molecules are significantly changed compared to the pristine model systems. In the excited-state geometry, ketonecontaining oligomers possess emissive excited states in the energy region of the experimentally observed low-energy emission band. The calculated infrared (IR) absorption peaks associated with the defects can also be correlated with the experimental IR spectra.