S
                  1
                ∼&amp;gt;T
                  1
           intersystem crossing in π-conjugated organic polymers

Burrows, Hugh D.; Melo, J. Sérgio Seixas de; Serpa, Carlos; Arnaut, Luı́s G.; Monkman, Andrew P.; Hamblett, I.; Navaratnam, S.

doi:10.1063/1.1413969

Cited by 115 publications

(118 citation statements)

References 40 publications

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“…From Table 2, it can be seen that the values for φ ∆ and φ T are quite similar indicating that these cruciform oligomers sensitize singlet oxygen formation with near unit efficiency (S ∆ ∼ 1). This is similar to the behavior observed with a wide range of conjugated polymers, 36 and provides strong support for the measured values of intersystem crossing quantum yields.…”

Section: Resultssupporting

confidence: 87%

Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

et al. 2008

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A comprehensive study has been undertaken of the electronic spectral and photophysical properties of two oligophenyl (BPH and BPHF) and one oligothienyl (BTF) swivel cruciforms involving measurements of absorption, fluorescence, and phosphorescence spectra, quantum yields of fluorescence (φ F ), phosphorescence (φ Ph ) and triplet formation (φ T ), lifetimes of fluorescence (τ F ) and of the triplet state (τ T ), and quantum yields of singlet oxygen production (φ ∆ ). From these, all radiative k F and radiationless rate constants, k IC and k ISC , have been obtained in solution. The energies of the lowest lying singlet and triplet excited states were also determined at 293 K. Several of the above properties have also been obtained at low temperature and in the solid state (thin films). In general, for the phenyl oligophenyl (BPH) and for the oligothienyl (BTF) compounds, the radiationless decay channels (φ IC + φ ISC ) are the dominant pathway for the excited-state deactivation, whereas with the fluorene based oligophenyl BPHF the radiative route prevails. In contrast to the general rule found for related oligomers (and polymers) where radiative emission from T 1 is absent, with the compounds studied, phosphorescence has been observed for all of the compounds, indicating that this type of functionalization can lead to emissive triplets. Time-resolved fluorescence decays with picosecond resolution revealed multiexponential (bi-and triexponential) decay laws compatible with the existence of more than one species or conformation in the excited state. These results are discussed on the basis of conformational flexibility in the excited state.

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Section: Resultssupporting

confidence: 87%

Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

et al. 2008

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“…1); this is a commonly observed feature with related compounds [7,17,18] and in particular with the correspondent polymers [15,29], and is attributed to the wide range of vibrational and rotational degrees of freedom available in conjugated oligomers and polymers [16]. Substitution of an alkyl (HPV3P) by an alkyloxy (EHOPV3P, MPOPV3A) sidechain red-shifted the absorption maximum of the compound by %67 nm for the ethylhexyloxy and %80 nm for the methylpropyl-oxy substituents, see Table 1 [7,17,18].…”

Section: Absorptionmentioning

confidence: 99%

“…1H-Phenalenone (perinaphthenone) in benzene (/ D = 0.93) was used as standard [21]. To check the precision of these values singlet oxygen yields were verified at the FRRF (Daresbury laboratories), with a set-up elsewhere described [15].…”

Section: Spectroscopic Measurementsmentioning

confidence: 99%

“…For such applications, one important drawback of these compounds is related to the formation of excited triplet states. These are expected to be the predominant species formed by charge recombination in electroluminescent devices (75 % from spin statistics) [4] and because singlet oxygen formation (via interaction with oxygen) is observed following photolysis of aerated solutions of conjugated polymers [15], it may have important implications in a device working and consequently lead to degradation of devices based on conjugated polymers [12]. Triplet states of conjugated polymers have, in the solid state, lifetimes of the order of a few milliseconds, which again make them very susceptible to degradation induced by light.…”

Section: Introductionmentioning

confidence: 99%

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Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

Melo

Pina

Paolo³

et al. 2006

Chemical Physics

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A comprehensive photophysical and spectroscopic study of a new class of p-phenylenevinylene oligomers (PPV-trimers) possessing different alkyl and alkyloxy sidechain substituents and different end groups (aldehyde, C@C, phenylene and anthracene units) was undertaken in solution at room temperature (293 K), low temperature (77 K) and in thin films. The study comprises absorption, emission and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion and singlet oxygen formation) and lifetimes. The data allow the determination of rate constants for all decay processes. From these, several conclusions could be drawn. Changing from alkyl to alkyloxy substituents does not change fluorescence and internal conversion yields but decreases the (already small) intersystem crossing yield. The introduction of anthracene at the terminal ends of the PPV-trimers leads to the lowest fluorescence yield reported in this study. Of particular importance is the fact that the fluorescence quantum yields in films are of the same order of magnitude as those in solution, which suggests the potential for use of these oligomers for light-emitting device applications. With one of the alkyloxy derivatives, a more detailed study of the early part of the fluorescence decay was made, and it was found that upon excitation a fast conformational relaxation process of the initially excited oligomer occurs, leading to a more planar conjugation segment.

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“…Hence the triplet yield can be considered as a minor factor in comparison to the non-radiative decay through the vibrational channels in the extended backbone of the polymer. To further reinforce this point it has been reported in MEH-PPV that of the total non-radiative yield of 0.76, the triplet contribution is only responsible for 0.01 [29]. It has also been documented that for PPV derivatives, such as MEH-PPV and cyano substituted PPVs, the inclusion of electron withdrawing side chains serves to prolong the fluorescence lifetime [30] as is the characteristic shown in our acene substituted series.…”

Section: Resultsmentioning

confidence: 61%

Correlation of vibrational intensity with fluorescence lifetimes in π conjugated polymers

O’Neill¹,

Lynch²,

McNamara³

et al. 2008

Polymer

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a b s t r a c tA series of novel pi (p) conjugated polymers, originating from the archetypical Polyphenylene vinylene, in which the phenyl units are successively replaced by the larger naphthyl and anthryl acene units, were previously found to have a well-defined relationship between their relative fluorescence yields and their vibrational characteristics, as determined by Raman spectroscopy. In this study the Strickler-Berg equation is used to probe the influence of continual substitution of higher order acene units into the conjugated backbone in terms of the variation of the radiative and non-radiative rates. The deconvolution of the radiative and non-radiative rates enables the correlation of the reduction of the Raman intensity and concomitant increase in the fluorescence yield with the reduction of the non-radiative rate. This confirms that the reduction of the non-radiative rate is the dominant process introduced by the vibrational confinement originating from systematic substitution of higher order acene units into the polymer backbone.

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S 1 ∼>T 1 intersystem crossing in π-conjugated organic polymers

Cited by 115 publications

References 40 publications

Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

Correlation of vibrational intensity with fluorescence lifetimes in π conjugated polymers

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S 1 ∼&gt;T 1 intersystem crossing in π-conjugated organic polymers

Cited by 115 publications

References 40 publications

Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

Correlation of vibrational intensity with fluorescence lifetimes in π conjugated polymers

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Product

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S 1 ∼>T 1 intersystem crossing in π-conjugated organic polymers