Mechanistic studies on the photodegradation of 2,5-dialkyloxyl-substituted para-phenylenevinylene oligomers by singlet oxygen

Abstract

Time-dependent UV/visible absorption changes are observed on photolysis of aerated solutions of monodisperse, vinyl end-capped 2,5-diheptyloxyl substituted PV-oligomers (OPV, n = 1, 2, 3). In all cases, photolysis occurs in at least two distinct stages. Evidence for the intermediacy of singlet oxygen comes from pulse radiolysis and time-resolved luminescence studies, which confirm formation of the OPV triplet state and its quenching by molecular oxygen to produce singlet oxygen. The subsequent reaction with oligomers is observed directly by time-resolved phosphorescence and indirectly through product identification. The results strongly suggest that the reaction between singlet oxygen and OPV proceeds via cycloaddition, leading to bond scission and aldehyde group formation. The reactivity of vinylene linkages is greater than of vinyl end groups. Consequently, the photostability decreases as the chain length is extended. Implications on the oxidative degradation of poly(p-phenylenevinylene)s in optoelectronic devices, and of competing singlet oxygen and superoxide radical anion degradation pathways, are discussed.

Separating Solvent and Conformational Effects on the Photophysics of a Homologous Progression of N-Terminated Phenylenevinylene Oligomers

“…From these experiments, it has been possible to determine the triplet absorption maxima ( λ T ), extinction coefficients ( ε T ), and triplet ( ϕ T ) and singlet oxygen ( ϕ Δ ) quantum yields, see Table . The transient triplet–triplet absorption spectrum for the trimer is similar to those reported for a related system , and shows depletion of the ground-state absorption between 350 and 500 nm and a broad absorption band ranging from 500 to 800 nm (Figure b) suggesting some delocalization of the excited triplet state . The transient triplet–triplet absorption spectra of the three oligomers are similar and have a maximum in the range of 650–680 nm.…”

Acene-linked conjugated polymers with ratiometric fluorescent response to 1O2

“…The rate of reaction between P2 and 1 O 2 was slow enough to allow observation of significant decomposition of the CP backbone. 32 These observations are consistent with formation of the tetracene-endoperoxide. Tetracene and rubrene are known to form endoperoxides in high yield via 1 O 2 cycloaddition.…”

Correlating triplet yield, singlet oxygen generation and photochemical stability in polymer/fullerene blend films

“…1 Photochemical stability studies on semiconducting polymers to date have focused on two possible oxygen dependent photodegradation pathways involving the generation of either singlet oxygen or superoxide radical anions. 2 Such studies to date have typically employed P3HT and poly(p-phenylenevinylenes) (PPVs), 3,4 and have primarily concluded that the dominant degradation pathway involves superoxide radical anions generated by polymer or fullerene anions. 4,5 The alternative singlet oxygen pathway, based on oxygen quenching of molecular triplet states, has received less attention, with most studies to date indicating this pathway is less significant.…”