Laser flash photolysis of poly(p-vinylbenzophenone) in solution. Intramolecular triplet deactivation processes

Poly(p‐vinylbenzophenone) (poly[1‐(4‐benzoylphenyl)ethylene], PVBP) and p‐isopropylbenzophenone (IPB) were irradiated in benzene solution at room temperature with 347, 1 nm laser flashes (duration 25 ns). Triplet‐triplet spectra were recorded at the end of the flash. Upon following the decay of the T‐T spectra a pronounced polymer effect was found: the decay followed 2nd order kinetics in the case of the polymer and 1st order kinetics in the case of the model compound. The halflife times differ by a factor of about five (τ1/2(PVBP) < τ1/2(IPB)). Whereas τ1/2(IPB) was not influenced, τ1/2(PVBP) decreased with increasing absorbed dose per flash. From the results it is inferred that at relatively high dose rates PVBP triplets decay essentially via intramolecular T‐T annihilation and at lower dose rates via intramolecular selfquenching processes. At comparable conditions IPB triplets were essentially deactivated via interactions with solvent molecules.