Singlet Oxygen as a Reactive Intermediate in the Photodegradation of Phenylenevinylene Oligomers

Dam, Niels Arne; Scurlock, Rodger D.; Wang, Bojie; Ma, Lichuan; Sundahl, and Mikael; Ogilby, Peter R.

doi:10.1021/cm9807687

Cited by 95 publications

(81 citation statements)

References 42 publications

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“…Since electroluminescence is normally only observed from the shortlived singlet excited state, long-lived triplet states may also act as traps to reduce the concentration of these species in devices [23]. Secondly, in the presence of molecular oxygen, triplet states may sensitise the formation of singlet oxygen, which can react with polymer chains, and ultimately limit device performance and lifetime [23][24][25][26][27]. On the beneficial side, the electronic energy from the triplet states of these systems may, however, be captured by appropriate acceptors, and these systems show potential as electrophosphorescent devices [28][29][30].…”

Section: Introductionmentioning

confidence: 99%

Triplet state dynamics on isolated conjugated polymer chains

et al. 2002

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Triplet state behaviour has been studied with several conjugated polymers in dilute benzene solutions by flash photolysis, photoacoustic calorimetry (PAC) and pulse radiolysis/energy transfer. With polythiophenes and the ladder poly(p-phenylene) MeLPPP, singlet-triplet intersystem crossing (ISC) is relatively efficient. In contrast, it is inefficient with poly(p-phenylenevinylene)s (PPVs) and polyfluorene, while with cyano-substituted PPV, there is no evidence for any long-lived triplet state. Energy transfer from triplet biphenyl to MEH-PPV is diffusion controlled and triplet state lifetimes are typically tens or hundreds of ls. All the triplet states are quenched by molecular oxygen, leading to formation of singlet oxygen with yields which are generally close to those for triplet formation. With pulse radiolysis at high doses, it is possible to have more than one triplet state per polymer chain. This can lead to delayed fluorescence via intrachain triplet-triplet annihilation. Kinetic analysis of this shows slow movement of triplets by hopping along the chain.

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Section: Introductionmentioning

confidence: 99%

Triplet state dynamics on isolated conjugated polymer chains

et al. 2002

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“…[30][31][32] Then, this singlet oxygen molecule attacks the chemical bonds of the polymer. The long lifetime of the triplet state of MEH-PPV (~100 μs in deoxygenated solution 33 ) provides enough time for such a reaction to occur.…”

Section: Resultsmentioning

confidence: 99%

Watching two conjugated polymer chains breaking each other when colliding in solution

et al. 2014

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While collision theory successfully describes the kinetics of chemical reactions, very little is known about the processes at the molecular level, especially if the reacting molecules are large. In this study, using single-molecule spectroscopy, we visually observed that collision between two conjugated polymer (CP) molecules in solution leads to simultaneous rupture of both chains. In addition to opening up the possibility of monitoring chemical processes in solution at the single-molecule level, these results demonstrate that mechanical bending of two stiff conjugated backbones against each other (the effect of leverage) by Brownian motion can weaken the chemical bond and markedly accelerate photochemical oxygen-induced chain scission by at least 20 times. The catalytic effect of the chain bending is also enhanced by a prolonged interaction between the chains owing to their entanglement. These findings are important for the solution processing of CPs in their application in organic electronics, for understanding the degradation mechanisms in CPs and for the development of new catalysts based on mechanical interactions with target molecules. NPG Asia Materials (2014) 6, e134; doi:10.1038/am.2014.91; published online 3 October 2014 INTRODUCTIONUnderstanding the chemical reaction mechanism at the molecular level is of great importance for designing new synthetic routes and developing new materials. After hundreds of years of practical chemistry, the mechanisms of many reactions have been qualitatively understood from the viewpoint of the electric properties of the reactants, such as the nucleophilicity and electrophilicity. 1 Collision theory was developed to describe the reaction kinetics at the beginning of the past century. 2 For the reaction to occur, the reactant molecules must collide with each other with a proper orientation and sufficient kinetic energy, as described by Evans and Polanyi 3 in their transition state theory. Although these approaches are based on mechanical interactions, their applications are often possible only phenomenologically simply because there is no experimental data revealing the mechanistic picture of the interactions between molecules of complicated geometries. Does the collision here only provide the chance of contact between the reactants or is a collision-induced mechanical force also involved? Is there any marked change of the molecular conformation that precedes the reaction?Indeed, more than a hundred years ago, it was discovered that a mechanical force can have a role in chemical reactions; this discovery gave birth to the field of mechanochemistry. 4,5 Excellent mechanochemical studies have been performed on large biomolecules and polymers, even at the single-molecule level. 6-8 However, mechanochemistry, as it is usually understood, requires the application of an additional force onto the reactants via, for example, pressure and flow gradients induced by ultrasound or special flow cells.

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“…This degradation continues until the device fails [2,3]. Studies have shown that substitution with electron withdrawing or donating substituents can alter the rate of degradation of electroluminescent polymers [4,5,6]. It has been found that substitution with electron donating alkyloxy side chains increases the rate of degradation of the polymer [4], while phenyl or cyano electron withdrawing substituents lead to a decrease in the rate of degradation, particularly if the substituent is placed on the vinylene bonds [5,6].…”

Section: Introductionmentioning

confidence: 99%

“…Studies have shown that substitution with electron withdrawing or donating substituents can alter the rate of degradation of electroluminescent polymers [4,5,6]. It has been found that substitution with electron donating alkyloxy side chains increases the rate of degradation of the polymer [4], while phenyl or cyano electron withdrawing substituents lead to a decrease in the rate of degradation, particularly if the substituent is placed on the vinylene bonds [5,6]. Trifluoromethyl substituted compounds have been shown to be particularly stable towards photo-oxidation accentuating the benefit of electron deficient vinylene linkages and pointing towards the vulnerability of this moiety to degradation [7].…”

Section: Introductionmentioning

confidence: 99%

Kinetic studies of the photo-degradation of poly(arylene vinylenes)

O’Neill¹,

Lynch²,

McGoldrick

et al. 2012

Journal of Luminescence

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe kinetics of the degradation of a homologous series of Poly phenylene vinylenes in which the phenylene units of the PPV structure are systematically substituted by naphthyl and anthyrl units is presented. Degradation is monitored according to the decay of the long wavelength absorption maximum upon illumination with UV radiation. Compared to Toluene solution, the photo-degradation is seen to be accelerated in Chloroform solution. All decays are fitted with first order kinetics. It is found that all substitutions improve the stability of the vinylene polymers against decay.In particular the highly electro-negative naphthyl group serves to drastically increase the stability due to electron depletion across the vinyl bond. The decay rate is shown to correlate well with the variation of the electronic properties of the backbone and with the reduction of vinylene bond strength as measured using Raman spectroscopy.

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Singlet Oxygen as a Reactive Intermediate in the Photodegradation of Phenylenevinylene Oligomers

Cited by 95 publications

References 42 publications

Triplet state dynamics on isolated conjugated polymer chains

Triplet state dynamics on isolated conjugated polymer chains

Watching two conjugated polymer chains breaking each other when colliding in solution

Kinetic studies of the photo-degradation of poly(arylene vinylenes)

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