Aggregation effects on the structure and optical properties of a model PPV oligomer

Collison, Christopher J.; Treemaneekarn, Varaporn; Oldham, Wilbur.; Hsu, J. N. C.; Rothberg, Lewis J.

doi:10.1016/s0379-6779(00)00899-7

Cited by 34 publications

(25 citation statements)

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“…A larger absorption cross-section corresponds to a longer chain length, which leads to higher probability for a specific morphology (chain-chain contact or aggregation) responsible for the "red" emission. [21,24,25,[40][41][42] …”

Section: Excitation Intensity Modulation Smsmentioning

confidence: 99%

Variable Temperature Single‐Molecule Dynamics of MEH‐PPV

et al. 2005

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Herein, we continue our investigation of the single-molecule spectroscopy of the conjugated polymer poly[2-methoxy,5-(2'-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) at cryogenic temperatures. First, the low temperature microsecond dynamics of single MEH-PPV conjugated polymer molecules are compared to the dynamics at room temperature revealing no detectible temperature dependence. The lack of temperature dependence is consistent with the previous assignment of the dynamics to a mechanism that involves intersystem crossing and triplet-triplet annihilation. Second, the fluorescence spectra of single MEH-PPV molecules at low temperature are studied as a function of excitation wavelength (i.e. 488, 543, and 568 nm). These results exhibit nearly identical fluorescence spectra for different excitation wavelengths. This strongly suggests that electronic energy transfer occurs efficiently to a small number of low-energy sites in the multichromophoric MEH-PPV chains.

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Section: Excitation Intensity Modulation Smsmentioning

confidence: 99%

Variable Temperature Single‐Molecule Dynamics of MEH‐PPV

et al. 2005

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“…[4,5] Complexity results from photophysical processes, which in dilute solution include solvent and/or conformational relaxation [3,[6][7][8][9][10] and intrachain energy transfer, [11][12][13] while in concentrated solution or in films they may also involve interchain energy transfer, [2] excimer formation [14] and formation of H or J aggregates. [15][16][17] The correct interpretation of this information is important for detecting, understanding and resolving problems such as imbalance of electron and hole injection currents, [18][19][20][21][22][23] decreased luminescence yields, which result from aggregation quenching that is dependent on the polymer concentration, [15][16][17] and chemical stability of the films.…”

Section: Introductionmentioning

confidence: 99%

Photodynamics of a PV Trimer in High‐Viscosity Solvents and in PMMA Films: A New Insight into Energy Transfer versus Conformational Relaxation in Conjugated Polymers

Paolo¹,

Morgado

Maçanita³

2009

ChemPhysChem

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Non-Stokes-Einstein relaxation: The rate constant of conformational relaxation of a phenylenevinylene trimer (see picture) in different solvents is proportional to eta(-alpha), with alpha values decreasing from close to unity (low viscosity) to zero at sufficiently high solvent viscosity. This behaviour is attributed to the flexible methylbutyl side chains of the trimer, which partially screen the solvent friction. The p-phenylenevinylene (PV) trimer (MBOPV3) was used to probe the effect of conformational relaxation on fluorescence decays of PV-based polymers in the high solvent viscosity regime, from n-hexadecane (3.45 cP at 293 K) to liquid paraffin (123 cP at 293 K), and in dilute poly(methyl methacrylate) (PMMA) solid films. The effect of intermolecular energy transfer and radiative transport on the fluorescence decays was also analysed by increasing the concentration of MBOPV3 in the PMMA films up to a pure MBOPV3 film. The rate constant of conformational relaxation was found to decrease with increasing solvent viscosity up to about 23 cP, but then becomes viscosity independent. The non-Stokes-Einstein behaviour of k(CR) versus eta over the whole viscosity range apparently results from the presence of the flexible methylbutyl side chains of MBOPV3, which partially screens the solvent friction. Conformational relaxation is not observed in very dilute PMMA solid films, where the fluorescence decay becomes single exponential. The decays become multi-exponential again with an increase of MBOPV3 concentration in the PMMA films, but in this case it is due to intermolecular (interchain) energy transfer from less planar to more planar conformations of MBOPV3. In the pure MBOPV3 film, interchain energy transfer (radiative and non-radiative) is the major process responsible for the observed (tetra-exponential) decays.

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“…The availability of soluble PPV oligomers makes it possible to study their intrinsic molecular properties, and extrapolate to the behaviour of the related polymer [5,7,13,14]. Moreover, the study of these compounds in dilute solutions allows their characterization in the absence of significant effects due to interchain interactions and under conditions where the time between collisions of two oligomers is longer than the lifetimes of the excited states under investigation.…”

Section: Introductionmentioning

confidence: 99%

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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Aggregation effects on the structure and optical properties of a model PPV oligomer

Cited by 34 publications

References 0 publications

Variable Temperature Single‐Molecule Dynamics of MEH‐PPV

Variable Temperature Single‐Molecule Dynamics of MEH‐PPV

Photodynamics of a PV Trimer in High‐Viscosity Solvents and in PMMA Films: A New Insight into Energy Transfer versus Conformational Relaxation in Conjugated Polymers

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

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