Author: Timothy McCalvin SmithPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Spectral Properties and Photophysics of Conjugated Polymers in Electric Fields
Author: Timothy McCalvin SmithPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Semiconducting Polymers
Author: Raquel Aparecida DominguesPublisher: CRC Press
ISBN: 1000727726
Category : Science
Languages : en
Pages : 220
Book Description
Semiconducting polymers are of great interest for applications in electroluminescent devices, solar cells, batteries, and diodes. This volume provides a thorough introduction to the basic concepts of the photophysics of semiconducting polymers as well as a description of the principal polymerization methods for luminescent polymers. Divided into two main sections, the book first introduces the advances made in polymer synthesis and then goes on to focus on the photophysics aspects, also exploring how new advances in the area of controlled syntheses of semiconducting polymers are applied. An understanding of the photophysics process in this kind of material requires some knowledge of many different terms in this field, so a chapter on the basic concepts is included. The process that occurs in semiconducting polymers spans time scales that are unimaginably fast, sometimes less than a picosecond. To appreciate this extraordinary scale, it is necessary to learn a range of vocabularies and concepts that stretch from the basic concepts of photophysics to modern applications, such as electroluminescent devices, solar cells, batteries, and diodes. This book provides a starting point for a broadly based understanding of photophysics concepts applied in understanding semiconducting polymers, incorporating critical ideas from across the scientific spectrum.
Understanding the Correlation Between Microscopic Morphology and Photophysical Properties of Conjugated Polymers by Optical Spectroscopy
Author: Liwei Wang (Chemist)Publisher:
ISBN:
Category :
Languages : en
Pages : 139
Book Description
"The unique photophysical and electronic properties of conjugated polymers (CPs) make them promising candidates for applications in displays, biosensors, field-effect transistors and photovoltaic devices. The photophysical properties of CPs are strongly dependent on the chain morphology. However, the understanding of the morphology-property correlation is still obscured both due to inhomogeneities in ensemble experiments and even due to multichromophoric properties in single chain experiments. In this dissertation, we constructed a single molecule spectroscopy apparatus and home-built MATLAB code together to correlate simultaneous measurements of intensity, lifetime and spectrum to learn more about proper photophysical models to describe the properties of CPs, the effect of O2, and the role of energy transfer in CPs. Bulk experiments in mixed solvents where chain conformations can be varied were also conducted to understand the CPs from a macroscopic perspective, where chain-chain interactions also play an important role. Especially, we selected three CPs to study, Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), Poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) and Poly(9,9-dioctylfluorene-alt-biselenophene) (F8Se2). In Chapter 3, data from mixed solvent experiments are known to produce biomodal distributions of spectra where chains emitting red light are thought to be in regions where chromophore aggregation is important. We showed in single molecule experiments that MEH-PPV follows the J-aggregate model where the properties of the chromophore are closely related to the conjugation length. Despite the similarity of the single molecule spectra to those observed in the bulk, fluorescence dynamics and intensities of red emitters are similar to those of blue emitters in the single molecule case. O2 mainly causes reversible quenching ("blinking") on the single MEH-PPV chains. Unfortunately, we could not reproduce flaring observed in a previous thesis and, although we had improved N2 protection and better signal to noise (S/N) ratio, we are not sure why our results are different. In Chapter 4 where we study F8T2, we also observe two distinct types of chromophores in the bulk experiments depending on the solvent quality. The photophysical properties of the F8T2 chains were well explained by the Spano HJ model. Even though spectral lineshapes of single F8T2 chains resemble those observed in the bulk, we concluded on the basis of very different emission intensity and lifetime behavior that the origin of the emission spectra is different and could be ascribed to bent chains. We argue that the propensity to bend in the F8T2 case and what makes it different than MEH-PPV derives from the presence of five-membered rings in F8T2 and we note behavioral similarities to polythiophenes that share this property. In Chapter 5, we showed that analogous CPs F8Se2 with selenium instead of sulfur in the monomer units exhibit strongly reduced fluorescence and dramatic reduction in singlet lifetime in the bulk due to heavy atom induced intersystem crossing to the triplet. Surprisingly, however, we observe substantial fluorescence and relatively strong emission in the single chain case for F8Se2. On the basis of a red shift in the spectrum and the long lifetimes relative to the bulk, we believe that the emission we are observing in this case is primarily from a photooxidized species similar to that observed in fluorene polymers. Overall, this work is a step towards looking more carefully at the complex correlation between morphology and photophysical properties. We show that bending of single chains can mimic the spectroscopy of aggregation and that it is necessary to consider fluorescence lifetime and efficiency data to distinguish between these effects. We have also used single chain spectroscopy to look at how chain morphology plays a significant role in energy transfer. In particular, we see little evidence for energy transfer in chains deposited from good solvents in contrast to some work where chains can behave as single chromophores when deposited under conditions where chains are able to collapse. We have also introduced a new way of looking at the relative propensity of different chains within a sample to blink and/or permanently photooxidize through studies correlating intensity drops and rises with spectra"--Pages x-xii.
Electronic and Optical Properties of Conjugated Polymers
Author: William BarfordPublisher: OUP Oxford
ISBN: 0191667048
Category : Technology & Engineering
Languages : en
Pages : 320
Book Description
Conjugated polymers have important technological applications, including solar cells and light emitting devices. They are also active components in many important biological processes. In recent years there have been significant advances in our understanding of these systems, owing to both improved experimental measurements and the development of advanced computational techniques. The aim of this book is to describe and explain the electronic and optical properties of conjugated polymers. It focuses on the three key roles of electron-electron interactions, electron-nuclear coupling, and disorder in determining the character of the electronic states, and it relates these properties to experimental observations in real systems. A number of important optical and electronic processes in conjugated polymers are also described. The second edition has a more extended discussion of excitons in conjugated polymers. There is also a new chapter on the static and dynamical localization of excitons.
Primary Photoexcitations In Conjugated Polymers: Molecular Exciton Versus Semiconductor Band Model
Author: Niyasi Serdar SariciftciPublisher: World Scientific
ISBN: 9814518212
Category : Science
Languages : en
Pages : 641
Book Description
This volume concentrates on the controversy within the scientific community over how to explain, understand and describe the photophysics/photochemistry of this class of materials.This controvery is of such a fundamental nature that the solution of the problem might be in a unification of the semiconductor and metal physics with the molecular quantum chemistry. Thus, a wide-ranging and comprehensive discussion of this very crucial issue has not been written down yet.This volume brings together the most prominent scientists specializing in this controversial topic. Each contributor addresses the opponents' arguments. After short introductory chapters, the contributors discuss their own speciality area and compare the results with both models and explain their position on why one of the models is more appropriate. Special emphasis is given to comparative discussions with other conjugated molecular systems as well as inorganic semiconductors.
Investigating the Photochemistry and Photophysics of Conjugated Polymers by Single Molecule Spectroscopy
Author: Dehong HuDissertation Abstracts International
Author: Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 850
Book Description
Resolving Puzzles in Conjugated Polymer Photophysics
Author: Chakraborty RajarshiPublisher:
ISBN:
Category :
Languages : en
Pages : 129
Book Description
"Conjugated polymers are active candidates of research for their potential applications in organic electronic devices. This thesis contains experimental results of the photophysical behaviour of Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) in the nanoseconds timescale. It is generally accepted that quantum yield of films are less than their solution counterparts and has a non-exponential "temporal tail" in the decay dynamics. This thesis reports the spectroscopy, excitation wavelength dependence, temperature dependence and electric field quenching of the temporal tail of the photoluminescence in MEH-PPV on a nanosecond timescale. We try to understand if a correlation exists between the "temporal tail" and quantum yield in films. We conclude that the tail represents emission from H-like aggregated regions in the polymer. Using a simple model of the photophysics, we estimate the formation yield of the aggregates responsible for the tail emission and conclude that they cannot account for the large reduction in fluorescence observed in densely packed films relative to that in solution. If recombination of injected charges in an OLED follows quantum spin statistics and all recombination forms the lowest excited states in a spin manifold, then the ratio of formed singlet to triplet exciton would be 1:3 setting an efficiency limit of 25% to the EL emission. However, in conjugated polymers, various studies have reported the formation ratio of singlet to triplet excitons to be greater than 1:3. These results have ambiguity due to issues of magnetoresistance, TTA, charge trapping, outcoupling etc. We try to reexamine the singlet-triplet branching ratio in Poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt- (benzo [2,1,3] thiadiazol-4,8-diyl) (F8BT) along with MEH-PPV with the hope of circumventing these problems. This approach involves simultaneous detection of singlet and triplet state luminescence and then estimate the recombination branching ratios directly from the change in singlet and triplet signals produced by applying magnetic fields. The role of PP in F8BT films are addressed based on studying the effect of external magnetic field on the DF and triplet signals of gold nanoparticle doped films. This work is unique and important because it includes a delay dependent magnetic field effect study of the DF suggesting that spin randomization of charge pairs is a fast process that occurs on the several hundred nanoseconds time scale. The magnetic field effect on the fluorescence persists to tens of microseconds and we argue that this apparent inconsistency implies the existence of an intermediate state in the recombination process that has implications for measurements and theoretical treatments of the singlet recombination fraction in electroluminescent conjugated polymers."--Pages ix-x.
Conjugated Polymer Surfaces and Interfaces
Author: W. R. SalaneckPublisher: Cambridge University Press
ISBN: 9780521544108
Category : Technology & Engineering
Languages : en
Pages : 176
Book Description
The authors illustrate the basic physics and materials science of conjugated polymers and their interfaces, particularly, but not exclusively, as they are applied to polymer-based light emitting diodes. The approach is to describe the basic physical and associated chemical principles that apply to these materials, which in many instances are different from those that apply to their inorganic counterparts. The main aim of the authors is to highlight specific issues and properties of polymer surfaces and interfaces that are relevant in the context of the emerging field of polymer-based electronics in general, and polymer-based light emitting diodes in particular. Both theoretical and experimental methods used in the study of these systems are discussed. This book will be of interest to graduate students and research workers in departments of physics, chemistry, electrical engineering and materials sciences studying polymer surfaces and interfaces and their application in polymer-based electronics.
Photophysics of Conjugated Polymers
Author: Tieneke E. DykstraPublisher:
ISBN: 9780494578650
Category :
Languages : en
Pages : 326
Book Description
Poly (para-phenylenevinylene) (PPV), and its derivatives such as poly [2-methoxy, 5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene] (MEH-PPV), are typical conjugated polymers. In order to implement conjugated polymers into processable electronics technologies, we must first understand their complex photophysical properties as their efficiencies depend on the balance between exciton recombination and charge carrier formation. The inherent complexities of these materials arise from entanglement of the pi-electron system with disorder and nuclear motions of the polymer backbone. This disorder breaks the polymer chain into conformational subunits which can couple, giving rise to a set of delocalized states formed by Coulombic interactions between proximate subunits. Characteristics of PPVs include high quantum yields, non-mirror image absorption and fluorescence line shapes, and large apparent Stokes' shifts. These properties are discussed in the context of the relationships between polymer conformation, electronic structure, coupling, disorder and polymer photophysics.These important influences are often manifest in the dynamics of what happens after photoexcitation. In this work, we present 3-pulse photon echo peak shift (3PEPS) studies of conjugated polymers in both solution and film. To elucidate timescales characteristic of relaxation processes, we have simulated the 3PEPS data simultaneously with absorption and fluorescence, observing a rapid localization of the exciton in the initial ∼ 20 fs. Additional contributions to the decay of the peakshift are discussed. We also present transient anisotropy data for PPV polymers and oligomers which is compared to dynamics simulation for isolated chains of PPVs. This work demonstrates the influence of microscopic structure on ultrafast dynamics. We show that relaxation between exciton states can lead to rapid depolarization of the anisotropy, even though the spatial extent of exciton migration may be small. Generally, the connection between conformation and electronic structure is a theme throughout this thesis.