Spectroscopic characterization of p-phenylene vinylene (PV) oligomers. Part II: Selected 2,5-diheptyl substituted PV-oligomers

Narwark, O.; Gerhard, A.; Meskers, Stefan C. J.; Brocke, Stephan; Thorn‐Csányi, Emma; Bäßler, H.

doi:10.1016/s0301-0104(03)00335-5

Cited by 31 publications

(38 citation statements)

References 20 publications

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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]. For the PPV-trimers with ethylhexyloxy sidechain (EHOPV3P) substitution of the terminal end groups by the aromatic phenylene (EHOPV3PB) and anthracene (EHOPV3PA) groups red-shifted the absorption maximum…”

Section: Absorptionmentioning

confidence: 66%

“…In this particular case the observed pattern should be related with the increase of the electron-donor characteristics of the substituents as the number of oxygen atoms increases. The electron-donor alkyloxy sidechain and terminal end groups will extend the p-p electrons of the oxygen atoms to the oligomer backbone and as consequence the HOMO-LUMO energy gap is significantly reduced [7,18]. This behaviour is also observed in the triplet state as can be noted by the high delocalization observed in this case as the number of oxygen atoms increases in the terminal and sidechain substituents.…”

Section: Triplet Statementioning

confidence: 73%

“…b The underlined values are the wavelength maxima. with the compounds possessing alkyloxy derivatives may lie in the structural modification induced by the alkyloxy vs. alkyl sidechain, as has previously been observed [7,17,18] and discussed theoretically [31]. The electrondonor characteristics of the alkyloxy group will extend the p-electrons of the oxygen atoms to the oligomer backbone and as consequence the absorption and emission wavelength maxima are lower in energy.…”

Section: Fluorescencementioning

confidence: 80%

“…The thin film absorption spectra of these compounds are, when compared with solution data, redshifted %5-8 nm, with the exception of EHOPV3P whose maxima in solution (RT) and film is 427 nm (see Table 1). The red-shift of the absorption and emission band upon going from solution to film can be attributed to the loss of conformational freedom, due to the rigid media where the oligomer is immobilized, minimizing twisting vibrations along the PPV-trimer backbone with the consequent lowering of the energy gap between the HOMO and LUMO orbitals, resulting in a red shift of the absorption and fluorescence spectra [18].…”

Section: Solid-state Spectroscopic Behaviourmentioning

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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Section: Absorptionmentioning

confidence: 66%

Section: Triplet Statementioning

confidence: 73%

Section: Fluorescencementioning

confidence: 80%

Section: Solid-state Spectroscopic Behaviourmentioning

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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“…The most intriguing result is the change in emission intensity for the vibronic band at $550 nm in relation to the zero-phonon band at $510 nm. To quantify this change, we estimated the Huang-Rhys parameter (S) using multi-Gaussian fitting as described by Narwark et al 21 Table II gives S for all samples. From the blueshift in the UV-Vis spectra in Fig.…”

Section: Resultsmentioning

confidence: 99%

Substrate/semiconductor interface effects on the emission efficiency of luminescent polymers

Therézio¹,

Piovesan²,

Anni³

et al. 2011

Journal of Applied Physics

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Ultrafast thermoreflectance techniques for measuring thermal conductivity and interface thermal conductance of thin films J. Appl. Phys. 108, 094315 (2010) Electric field controlled Faraday rotation in an electro-optic/magneto-optic bilayer Appl. Phys. Lett. 97, 011901 (2010) Linear and nonlinear optical properties of gold nanoparticle-Eu oxide composite thin films J. Appl. Phys. 104, 033110 (2008) Intensity-dependent enhancement of saturable absorption in PbS-Au4 nanohybrid composites: Evidence for resonant energy transfer by Auger recombination Appl. Phys. Lett. 92, 251106 (2008) Raman imaging of doping domains in graphene on SiO2 Appl. Phys. Lett. 91, 241907 (2007) Additional information on J. Appl. Phys. The importance of interface effects for organic devices has long been recognized, but getting detailed knowledge of the extent of such effects remains a major challenge because of the difficulty in distinguishing from bulk effects. This paper addresses the interface effects on the emission efficiency of poly(p-phenylene vinylene) (PPV), by producing layer-by-layer (LBL) films of PPV alternated with dodecylbenzenesulfonate. Films with thickness varying from $15 to 225 nm had the structural defects controlled empirically by converting the films at two temperatures, 110 and 230 C, while the optical properties were characterized by using optical absorption, photoluminescence (PL), and photoluminescence excitation spectra. Blueshifts in the absorption and PL spectra for LBL films with less than 25 bilayers (<40-50 nm) pointed to a larger number of PPV segments with low conjugation degree, regardless of the conversion temperature. For these thin films, the mean free-path for diffusion of photoexcited carriers decreased, and energy transfer may have been hampered owing to the low mobility of the excited carriers. The emission efficiency was then found to depend on the concentration of structural defects, i.e., on the conversion temperature. For thick films with more than 25 bilayers, on the other hand, the PL signal did not depend on the PPV conversion temperature. We also checked that the interface effects were not caused by waveguiding properties of the excited light. Overall, the electronic states at the interface were more localized, and this applied to film thickness of up to 40-50 nm. Because this is a typical film thickness in devices, the implication from the findings here is that interface phenomena should be a primary concern for the design of any organic device.

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Conformational Relaxation of p‐Phenylenevinylene Trimers in Solution Studied by Picosecond Time‐Resolved Fluorescence

Paolo¹,

et al. 2007

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Two p-phenylenevinylene (PV) trimers, containing 3'-methylbutyloxyl (in MBOPV3) and 2'-ethylhexyloxyl (in EHOPV3) side chains, are used as model compounds of PV-based conjugated polymers (PPV) with the purpose of clarifying the origin of fast (picosecond time) components observed in the fluorescence decays of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV). The fluorescence decays of MBOPV3 and EHOPV3 reveal the presence of similar fast components, which are assigned to excited-state conformational relaxation of the initial population of non-planar trimer conformers to lower-energy, more planar conformers. The rate constant of conformational relaxation k(CR) is dependent on solvent viscosity and temperature, according to the empirical relationship k(CR)=aeta(o) (-alpha)exp(-alphaE(eta)/RT), where aeta(o) (-alpha) is the frequency factor, eta(o) is the pre-exponential coefficient of viscosity, E(eta) is the activation energy of viscous flow. The empirical parameter alpha, relating the solvent microscopic friction involved in the conformational change to the macroscopic solvent friction (alpha=1), depends on the side chain. The fast component in the fluorescence decays of MEH-PPV polymers (PPVs), is assigned to resonance energy transfer from short to longer polymer segments. The present results call for revising this assignment/interpretation to account for the occurrence of conformational relaxation, concurrently with energy transfer, in PPVs.

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Spectroscopic characterization of p-phenylene vinylene (PV) oligomers. Part II: Selected 2,5-diheptyl substituted PV-oligomers

Cited by 31 publications

References 20 publications

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

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

Substrate/semiconductor interface effects on the emission efficiency of luminescent polymers

Conformational Relaxation of p‐Phenylenevinylene Trimers in Solution Studied by Picosecond Time‐Resolved Fluorescence

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