Controlling the absorption and emission properties of polyparaphenylenevinylene films (original) (raw)
Related papers
Journal of Non-Crystalline Solids, 2006
In this work, we studied the absorption and emission spectra of spin-coated poly(p-phenylene vinylene) (PPV)-dodecylbenzenesulfonic counter-ion (DBS) films. The PPV-DBS films were obtained from a soluble precursor polymer thermally converted to PPV over a comparatively short time interval (30 min), and at low temperature (110°C), conditions that yielded films with few structural defects. The line shape of the absorption spectra of the films deposited on glass substrates was analyzed by assuming a Gaussian distribution of segments along the main chain of PPV, and a conjugation degree between 3 and 15 units. For emission studies, only PPV segments with a high conjugation degree or a lower energy gap (HOMO-LUMO transition) contributed to the feature of the spectra.
Correlation between emission and structural properties of poly(p-phenylene vinylene) thin films
Synthetic Metals, 2013
In this work we used different methods and parameters of deposition in order to obtain thin films of poly(p-phenylene vinylene) (PPV) with different structural properties. These properties were characterized by measurements of absorbance, Raman scattering, and photoluminescence (PL) as a function of temperature. The analysis of experimental data allowed us to observe the dependence of optical spectra with the effective conjugation length and the interaction between the polymer chains. In particular, we were able to correlate the dependence of the PL line shape with temperature and the values of emission anisotropy factor of the films with the intra and interchains energy migration processes. These results led us to conclude that such processes are essential ingredients for a proper analysis of the optical response of thin films of conjugated polymers.
Photoinduced photoluminescence intensity enhancement in poly"p-phenylene vinylene… films
We report measurements of photoluminescence ͑PL͒ intensity enhancement in poly͑p-phenylene vinylene͒ ͑PPV͒ films induced by light irradiation in the presence of air. This effect is dependent on laser intensity and the ratio between film thickness and excitation penetration depth. The results suggest that an efficient spectral diffusion of excited carriers to nondegraded PPV segments by Förster energy transfer is an important consideration in the PL efficiency of conjugated polymers light-irradiated in air.
Optical absorption and luminescence in poly(4,4′-diphenylenediphenylvinylene)
Synthetic Metals, 1985
Poly(4,4'-diphenylenediphenylvinylene), PDPV, is a soluble conjugated polymer that shows a degree of conjugation similar to that in poly-(paraphenylene). The optical properties of thin films exposed to AsF s show the appearance of features below the ~-~r* gap at 3 eV that can be interpreted in a model of dopant-induced polaron and bipolaron defects. When excited above the 7r-~* gap, PDPV shows a strong luminescence peaked at 2.4 eV. The Stokes' shift of 1 eV can be accounted for by radiative decay from a photogenerated polaron-exciton defect.
Physical Review B, 1996
We present measurements of the optical absorption and emission properties of poly(p-phenylene vinylene͒ ͑PPV͒-related materials focusing on the differences between molecules isolated by dispersion in an inert host and concentrated molecular films. Optical absorption spectra, photoluminescence ͑PL͒ spectra, PL efficiency, and time-resolved PL spectra of dilute blends of PPV oligomers with 2-5 phenylene-phenyl rings are compared with those of dense oligomer and polymer films. In dilute oligomer-poly͑methyl methacrylate͒ ͑PMMA͒ blends with high PL efficiency, the PL decay is exponential, independent of both temperature and oligomer length. This implies that the fundamental radiative lifetime of PPV oligomers is essentially independent of oligomer length. Concentrated spin-cast oligomer films and polymers have a faster and strongly temperaturedependent PL decay that approaches that of the dilute oligomer results at low temperature. The differences in PL decay correspond to changes in PL efficiency. The efficiency of the oligomer-PMMA blend is high and only weakly temperature dependent, whereas that of concentrated films is lower and strongly temperature dependent, decreasing by more than a factor of 3 from 10 to 350 K. The quenching of the PL efficiency in concentrated films is due to migration to extrinsic, impurity related centers as opposed to an intrinsic intermolecular recombination process. The PL spectrum of a dilute oligomer blend redshifts substantially, both as the excitation energy is decreased and as the emission time increases. This spectral redshift is due to disorderinduced site-to-site variation and not to diffusion to lower-energy sites. In contrast, no spectral shift with excitation energy or emission time was observed for dense oligomer films. ͓S0163-1829͑96͒03132-3͔
Conjugation Length Distribution in Poly(p-phenylenevinylene) (PPV) Films
The Journal of Physical Chemistry A, 2016
We studied the absorption line-shape of poly(pphenylenevinylene) (PPV) films deposited via spin coating and Langmuir−Blodgett techniques with the intent of identifying the conjugation length distribution in these two types of films, a key morphological aspect of conjugated polymer films. We treated the excitons in the polymer as independent oligomer excitons and modeled the absorption spectra of the individual oligomers using simple expressions for the oligomer size dependence of the gap energy, the line-broadening factor, the transition dipole moment and the Huang−Rhys parameter. We validated these expressions by independent measurements on phenyl-based oligomers and Density Functional Theory calculations. Our results show clear evidence that, for both types of PPV films, the conjugation length distribution depends exponentially on the segment size. Our results also set a lower limit, of about ten repeat units, for the maximum exciton length of three different phenyl-based oligomers.
Induced Secondary Structure in Nanostructured Films of Poly(<I>p</I>-phenylene vinylene)
Journal of Nanoscience and Nanotechnology, 2009
The control of emission properties in luminescent polymers such as poly(p-phenylene vinylene) (PPV) is important for various applications, and may be achieved with suitable molecular architectures in nanostructured films. This paper reports on optical properties of PPV films, using ellipsometry measurements for emitted light in the scope of the Stokes' theory. Organized PPV films obtained with the Langmuir-Blodgett (LB) method exhibited high degree of polarization for the emitted light, while cast films emitted mainly non-polarized light. From ellipsometry data, a secondary structure was inferred for poly(xylylidene tetrahydrothiophenium) chloride (PTHT), a PPV precursor, in solution, which is retained only to a small extent in the PPV cast film as thermal conversion was performed close to the glass transition temperature of PPV. On the other hand, a higher intensity of emitted light with circular polarization was observed for the LB film, which is attributed to PPV molecular secondary structure that was enhanced during the LB film deposition. Circular dichroism experiments were performed to corroborate this hypothesis. It is suggested that such a secondary structure has not been predicted in theoretical models for PPV because possible conformational changes induced in the processing steps are not taken into account.
1995
In this paper, we present the experimental absorption spectra and photoluminescence excitation spectra of poly(p-phenylene vinylene) (PPV). We also present the theoretically calculated absorption and photoluminescence spectra of PPV. The singlet-to-singlet transition energies and moments calculated from the intermediate neglect of differential overlap with the spectroscopic parametrization (INDO/S) semi-empirical method were used to analyze the absorption spectra. The symmetrical vibrational modes calculated from the abinitio method were used to obtain the vibronic features in the spectra of PPV. It is demonstrated that the inhomogeneity observed in the absorption spectra of PPV can be modeled by summing up the absorption of PPV oligomers with different chain lengths. The difference between absorption and photoluminescence excitation spectra is explained.
The efficiency and time-dependence of luminescence from poly (p-phenylene vinylene) and derivatives
Chemical Physics Letters, 1993
We report measurements of the quantum efficiency and time decay of photoluminescence in the conjugated polymers poly(g phenylenevinylene) (PPV) and poly(Z-methoxy, 5-(2'ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV). MEH-PPV is soluble and we measure values for the quantum yield for luminescence of order 35% for dilute solutions in toluene and chloroform. By comparison of luminescence decay rates in solution and in solid films we estimate luminescence efticiencies in solid films, which can be as high as 50% in partially conjugated PPV. Decay time distribution analysis of the luminescence reveals a broad distribution of decay rates, and this is consistent with the distribution of conjugation lengths known to be present in these materials. Exciton migration in better conjugated material results in narrower distributions of emitting chromophores.
Journal of Applied Polymer Science, 2009
Two classes of light emitting Poly(p-phenylenevinylene) (PPV) based conjugated-nonconjugated copolymers (CNCPs) have been synthesized. The conjugated chromophores containing 2-methoxy-5-(2 0-ethylhexyloxy)-1,4-phenylenevinylene (MEHPV) and 2,5-dimethyl-1,4-phenylenevinylene (DMPV) moieties are rigid segments and nonconjugated portion containing hexyl units are flexible in nature. All copolymers were synthesized by wellknown Wittig reaction between the appropriate bisphosphonium salts and the dialdehyde monomers. The resulting polymers were found to be readily soluble in common organic solvents like chloroform, THF and chlorobenzene. The effect of chromophore substituents on the optical and redox properties of the copolymers has been investigated. Color tuning was carried out by varying the molar percentage of the comonomers. The UV-Vis absorption and PL emission of the copolymers were in the range 314-395 nm and 494-536 nm respectively. All the polymers show good thermal stability. Polymer light-emitting diodes (PLEDs) were fabricated in ITO/PEDOT:PSS/emitting polymer/ cathode configurations of selected polymers using doublelayer, LiF/Al cathode structure. The emission maxima of the polymers were around 499-536 nm, which is a bluegreen part of the color spectrum. The threshold voltages of the EL polymers were in the range of 5.4-6.2 V. V