Download or read book Study of Triplet Exciton Dynamics in Small Organic Molecule Films Using Time Resolved Optical Spectroscopy written by Vygintas Jankus and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years it has become clear that knowledge of triplet transport in single layer and multilayer films can be crucial in improving the efficiency of organic light emitting devices and solar cells. This thesis reports an investigation of triplet exciton dynamics in small organic molecule single and multilayer layer films using optical time resolved nanosecond spectroscopy. A diligent step by step approach, leading towards the investigation of complex donor/spacer/acceptor multilayer structures is used. First of all, single layer films to be a constituents of multilayer structures were studied by measuring fluorescence, delayed fluorescence and phosphorescence. 4,4?-N, N?-dicarbazolyl-1,1?-biphenyl (CBP) widely used in organic light emitting diodes is characterized. Evidence is provided that in some of these spectra emission comes from trap states rather than the CBP molecule itself. Also N, N?-diphenyl-N, N?-bis(1-naphthyl)-1,1?-biphenyl-4,4??-diamine (NPB) has been investigated. Results indicate that bimolecular triplet recombination is dominant and that triplet transport has dispersive features even at room temperature in NPB films. Then films of heavy metal iridium complexes fac-tris(2-phenylpyridine) iridium (Ir(ppy)3) and iridium(III)tris(1-phenylisoquinoline) (Ir(piq)3) are put into the spotlight. New states previously not reported are identified and decay with the slope -1 characteristic of more than one iridium complex and previously not published in literature is observed. Triplet interface sites in bilayer Ir(piq)3/NPB films obstructing triplet migration are determined and triplet movement across interface is experimentally captured for the first time. The origin of these interface trap states is suggested. Then this system is upgraded into Ir(ppy)3/NPB/Ir(piq)3 and triplet transfer from Ir(ppy)3 to Ir(piq)3 via NPB is investigated. A model of triplet exciton dynamics in Ir(piq)3/NPB films using classical diffusion equations is presented with interface sites included. Computer simulations were performed and the results are in very good agreement with the experimental ones. Finally problems encountered are identified and main guidelines on how to do research in complicated multilayer structures are set.
Download or read book Relating Nanoscale Structure to Electronic Function in Organic Semiconductors Using Time resolved Spectroscopy written by Christopher Grieco and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular packing arrangements at the nanoscale level significantly contribute to the ultimate photophysical properties of organic semiconducting materials used in solar energy conversion applications. Understanding their precise structure-function relationships will provide insights that can lead to chemical and structural design rules for the next generation of organic solar cell materials. In this work, two major classes of materials were investigated: Singlet fission sensitizers and semiconducting block-copolymers. By exploiting chemical design and film processing techniques, a variety of controllable nanoscale structures could be developed and related to their subsequent photophysical properties, including triplet and charge transport. Time-resolved optical spectroscopies, including both absorption and emission techniques, were used to measure the population dynamics of excited states and charge carriers following photoexcitation of the semiconducting materials. Singlet fission, an exciton multiplication reaction that promises to boost solar cell efficiency by overcoming thermalization loss, has been characterized in several organic molecules. If the energetics are such that the excited state singlet energy is at least twice the triplet energy, then a singlet exciton may split into two triplet excitons through an intermolecular energy-sharing process. The thin film structure of a model singlet fission compound was exploited by modulating its crystallinity and controlling polymorphism. A combination of visible, near-infrared, and mid-infrared transient absorption spectroscopies were used to investigate the precise singlet fission reaction mechanism. It was determined that the reaction intermediates consist of bound triplet pairs that must physically separate in order to complete the reaction, which results in multiplied, independent triplet excitations. Triplet transfer, which is modulated by molecular packing arrangements that control orbital overlap coupling, was found to determine the efficacy of triplet pair separation. Furthermore, the formation of these independent triplets was found to occur on longer (picosecond) timescales than previously believed, indicating that any kinetically competing relaxation processes, such as internal conversion, need to be controlled. Last, it was found that the diffusion of the multiplied triplet excitons, and thus their harvestability in devices, is highly influenced by the crystallinity of the material. In particular, the presence of even a small amount of contaminant amorphous phase was determined to be detrimental to the ultimate triplet diffusion length. Future research directions are outlined, which will be used to develop further chemical and structural design rules for the next generation of singlet fission chromophores. Semiconducting block-copolymers, because of their natural tendency to self-assemble into ordered nanoscale structures, offer an appealing strategy for controlling phase segregation between the hole and electron transport materials in organic solar cells. Such phase segregation is important for both ensuring efficient conversion of the photogenerated excitons into charge carriers, and for creating percolation pathways for efficient transport of the charges to the device electrodes. Time-resolved mid-infrared spectroscopy was developed for monitoring charge recombination kinetics in a series of block-copolymer and polymer blend films possessing distinct, controlled nanoscale morphologies. In addition to explaining previous work that correlated film structure to device efficiency, it was revealed how the covalent linkage in block-copolymers can be carefully designed to prevent rapid recombination losses. Furthermore, novel solution-phase systems of block-copolymer aggregates and nanoparticles were developed for future fundamental spectroscopic work. Future studies promise to explain precisely how polymer chain organization, including intrachain and interchain interactions, governs their ultimate charge photogeneration and transport properties in solar cells.
Download or read book Advanced EPR written by A.J. Hoff and published by Elsevier. This book was released on 2012-12-02 with total page 943 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advanced EPR: Applications in Biology and Biochemistry provides an up-to-date survey of existing EPR techniques and their applications in biology and biochemistry, and also provides a wealth of ideas for future developments in instrumentation and theory. The material is broadly organized into four parts. In the first part (chapters 1 to 6) pulsed EPR is discussed in detail. The second part (chapters 7 to 12) provides detailed discussions of a number of novel and experimental methods. The third part comprises seven chapters on double-resonance techniques, five on ENDOR and two on optically- and reaction yield-detected resonance. The final part is devoted to a thorough discussion of a number of new developments in the application of EPR to various biological and biochemical problems. Advanced EPR will interest biophysicists, physical biochemists, EPR spectroscopists and others who will value the extensive treatment of pulsed EPR techniques, the discussion of new developments in EPR instrumentation, and the integration of theory and experimental details as applied to problems in biology and biochemistry.
Download or read book Quantitative EPR written by Gareth R. Eaton and published by Springer Science & Business Media. This book was released on 2010-04-10 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: There is a growing need in both industrial and academic research to obtain accurate quantitative results from continuous wave (CW) electron paramagnetic resonance (EPR) experiments. This book describes various sample-related, instrument-related and software-related aspects of obtaining quantitative results from EPR expe- ments. Some speci?c items to be discussed include: selection of a reference standard, resonator considerations (Q, B ,B ), power saturation, sample position- 1 m ing, and ?nally, the blending of all the factors together to provide a calculation model for obtaining an accurate spin concentration of a sample. This book might, at ?rst glance, appear to be a step back from some of the more advanced pulsed methods discussed in recent EPR texts, but actually quantitative “routine CW EPR” is a challenging technique, and requires a thorough understa- ing of the spectrometer and the spin system. Quantitation of CW EPR can be subdivided into two main categories: (1) intensity and (2) magnetic ?eld/mic- wave frequency measurement. Intensity is important for spin counting. Both re- tive intensity quantitation of EPR samples and their absolute spin concentration of samples are often of interest. This information is important for kinetics, mechanism elucidation, and commercial applications where EPR serves as a detection system for free radicals produced in an industrial process. It is also important for the study of magnetic properties. Magnetic ?eld/microwave frequency is important for g and nuclear hyper?ne coupling measurements that re?ect the electronic structure of the radicals or metal ions.
Download or read book Single Molecule Spectroscopy written by R. Rigler and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 375 pages. Available in PDF, EPUB and Kindle. Book excerpt: The topics range from single molecule experiments in quantum optics and solid-state physics to analogous investigations in physical chemistry and biophysics.
Download or read book Diradicaloids written by Jishan Wu and published by CRC Press. This book was released on 2022-04-01 with total page 638 pages. Available in PDF, EPUB and Kindle. Book excerpt: π-Conjugated molecules with an even number of π-electrons usually have a closed-shell ground state. However, recent studies have demonstrated that a certain type of molecules could show open-shell singlet ground state and display diradical-like (diradicaloid) behavior. Their electronic structure can be understood in terms of the “diradical character” and “aromaticity” concepts. They display very different electronic properties from traditional closed-shell π-conjugated molecules and could be used as next-generation molecular materials. This book provides a comprehensive review on the chemistry, physics, and material applications of open-shell singlet diradicaloids. Particularly, it elaborates the fundamental structure–diradical character–electronic property relationships both theoretically and experimentally. The book has been written by leading scientists in the field from Japan, Germany, Spain, Italy, China, and Singapore.
Download or read book Handbook of Organic Conductive Molecules and Polymers Conductive Polymers written by Hari Singh Nalwa and published by Wiley. This book was released on 1997 with total page 736 pages. Available in PDF, EPUB and Kindle. Book excerpt: Das erste interdisziplinär orientierte, umfassende Handbuch leitfähiger Moleküle und Polymere! Namhaft Spezialisten haben Wissenswertes zu einer unglaublichen Vielfalt organischer Leiter und Supraleiter zusammengetragen - von chemischen und physikalischen Eigenschaften bis zu technologischen und anwendungsbezogenen Fakten. Reich bebildert und mit über 13000 Literaturzitaten!
Download or read book Organic Optoelectronic Materials written by Yongfang Li and published by Springer. This book was released on 2015-05-30 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume reviews the latest trends in organic optoelectronic materials. Each comprehensive chapter allows graduate students and newcomers to the field to grasp the basics, whilst also ensuring that they have the most up-to-date overview of the latest research. Topics include: organic conductors and semiconductors; conducting polymers and conjugated polymer semiconductors, as well as their applications in organic field-effect-transistors; organic light-emitting diodes; and organic photovoltaics and transparent conducting electrodes. The molecular structures, synthesis methods, physicochemical and optoelectronic properties of the organic optoelectronic materials are also introduced and described in detail. The authors also elucidate the structures and working mechanisms of organic optoelectronic devices and outline fundamental scientific problems and future research directions. This volume is invaluable to all those interested in organic optoelectronic materials.
Download or read book Exciton Coherence in 1D Phthalocyanine Based Organic Crystalline Thin Films written by KimNgan Burrill and published by . This book was released on 2020 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum coherence plays a vital role in the excitonic properties of organic semiconductors. Several theoretical and experimental studies have shown an unprecedented role of coherence in charge transfer and transport processes, which in turn can improve the performance of electronic devices. Specifically, an enhancement of exciton coherence size can result in fast energy transport and efficient charge separation. The ability to tailor the design and performance of organic electronics based on exciton coherence effects represents the possibility of ultrafast electronic applications in communication and information technology. The objective of this thesis is the excitonic coherence studies of 1D crystalline thin films of phthalocyanine-based organic semiconductors using steady-state and time-resolved photoluminescence spectroscopy (TRPL). One of the main focuses of this work is on investigating the correlation of intermolecular interactions, $\pi$ orbital overlap and dynamic disorders on the excitonic coherent behaviors in crystalline thin films of various phthalocyanine derivatives (i.e. H$_2$TPP, H$_2$OBPc, H$_2$OCPc, and H$_2$OBNc). Specifically, coherence lengths, exciton-phonon coupling strengths and the nearest neighbor (NN) interaction strengths are determined via: (1) the PL ratio of the excitonic coherence transition and its first vibrational replica and (2) the temperature evolution of radiative recombination lifetimes of coherent excitons. This study showed that the optimum coherence size and the robustness of excitonic coherence can be achieved by a complex interplay between NN interaction, vibrational energies and the coupling to vibrational modes. In particular, it is shown that the shortest NN distance does not ensure the achievement of maximum coherence length within the four investigated phthalocyanine species. Instead, the largest coherence length is measured in the octabutoxy derivative, where the saddle shape of the molecule and crystalline packing results in weaker coupling to the acoustic phonons modes despite having larger intermolecular NN distance. In addition, the effect of static and dynamic disorders on the behavior of exciton coherence is explored by alloying two phthalocyanine derivatives that are close in band gap energies and possess large coherence lengths, H$_2$OBPc and H$_2$OBNc. This study demonstrated the successful tuning of exciton coherence lengths and excitonic parameters in organic analogues of semiconductor alloys, H$_2$OBNc$_x$H$_2$OBPc$_{1-x}$. Furthermore, the correlation of exciton-phonon coupling and radiative recombination rate of coherent excitons with increasing alloy concentration or static disorders are successfully revealed.
Download or read book Polariton Chemistry written by Joel Yuen-Zhou and published by . This book was released on 2023-05-09 with total page 452 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a pedagogical introduction to the emerging field of Polariton Chemistry, where optical cavities are utilized to control the physicochemical properties and dynamics of molecular systems. Given the early stages of this interdisciplinary research area, it is important to provide a common language and starting point for interested researchers across Chemistry, Physics, and Engineering This edited compendium fills a void given that there is currently no analogue in the current literature. Topics covered include Single-Molecule Strong Light-Matter Coupling; Collective Strong Light-Matter Coupling; and Ultrastrong Light-Matter Coupling
Download or read book Physics Briefs written by and published by . This book was released on 1994 with total page 1224 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Electronic Processes in Organic Semiconductors written by Anna Köhler and published by John Wiley & Sons. This book was released on 2015-06-08 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first advanced textbook to provide a useful introduction in a brief, coherent and comprehensive way, with a focus on the fundamentals. After having read this book, students will be prepared to understand any of the many multi-authored books available in this field that discuss a particular aspect in more detail, and should also benefit from any of the textbooks in photochemistry or spectroscopy that concentrate on a particular mechanism. Based on a successful and well-proven lecture course given by one of the authors for many years, the book is clearly structured into four sections: electronic structure of organic semiconductors, charged and excited states in organic semiconductors, electronic and optical properties of organic semiconductors, and fundamentals of organic semiconductor devices.
Download or read book Exciton Dynamics in Lead Halide Perovskite Nanocrystals written by Bernhard Johann Bohn and published by Springer Nature. This book was released on 2021-05-18 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: Less than a decade ago, lead halide perovskite semiconductors caused a sensation: Solar cells exhibiting astonishingly high levels of efficiency. Recently, it became possible to synthesize nanocrystals of this material as well. Interestingly; simply by controlling the size and shape of these crystals, new aspects of this material literally came to light. These nanocrystals have proven to be interesting candidates for light emission. In this thesis, the recombination, dephasing and diffusion of excitons in perovskite nanocrystals is investigated using time-resolved spectroscopy. All these dynamic processes have a direct impact on the light-emitting device performance from a technology point of view. However, most importantly, the insights gained from the measurements allowed the author to modify the nanocrystals such that they emitted with an unprecedented quantum yield in the blue spectral range, resulting in the successful implementation of this material as the active layer in an LED. This represents a technological breakthrough, because efficient perovskite light emitters in this wavelength range did not exist before.
Download or read book Conference Papers Index written by and published by . This book was released on 1979 with total page 582 pages. Available in PDF, EPUB and Kindle. Book excerpt: Monthly. Papers presented at recent meeting held all over the world by scientific, technical, engineering and medical groups. Sources are meeting programs and abstract publications, as well as questionnaires. Arranged under 17 subject sections, 7 of direct interest to the life scientist. Full programs of meetings listed under sections. Entry gives citation number, paper title, name, mailing address, and any ordering number assigned. Quarterly and annual indexes to subjects, authors, and programs (not available in monthly issues).
Download or read book American Doctoral Dissertations written by and published by . This book was released on 1992 with total page 796 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Organic Solid State Lasers written by Sébastien Forget and published by Springer. This book was released on 2013-07-03 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic lasers are broadly tunable coherent sources, potentially compact, convenient and manufactured at low-costs. Appeared in the mid 60’s as solid-state alternatives for liquid dye lasers, they recently gained a new dimension after the demonstration of organic semiconductor lasers in the 90's. More recently, new perspectives appeared at the nanoscale, with organic polariton and surface plasmon lasers. After a brief reminder to laser physics, a first chapter exposes what makes organic solid-state organic lasers specific. The laser architectures used in organic lasers are then reviewed, with a state-of-the-art review of the performances of devices with regard to output power, threshold, lifetime, beam quality etc. A survey of the recent trends in the field is given, highlighting the latest developments with a special focus on the challenges remaining for achieving direct electrical pumping of organic semiconductor lasers. A last chapter covers the applications of organic solid-state lasers.
Download or read book Electron Spin Resonance Spectroscopy of Organic Radicals written by Fabian Gerson and published by John Wiley & Sons. This book was released on 2003-09-19 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electron spin resonance spectroscopy is the method used to determine the structure and life expectancy of a number of radicals. Written by Fabian Gerson and Walter Huber, top experts in the field of electron spin resonance spectroscopy, this book offers a compact yet readily comprehensible introduction to the modern world of ESR. Thanks to its comprehensive coverage, ranging from fundamental theory right up to the treatment of all important classes of organic radicals and triplet-state molecules that can be analyzed using ESR spectroscopy, this unique book is suitable for users in both research and industry. Instead of using complex mathematical derivations, the authors present a readily understandable approach to the field by interpreting sample spectra and classifying experimental data. In short, the ideal book for newcomers to the subject and an absolute must-have for everyone confronted with ESR spectroscopy and wanting to become acquainted with this widely-used method of analysis.
