Download or read book Studies of Singlet Exciton Fission in Perylenediimide Films and Triplet Exciton Transfer at Organic inorganic Interfaces written by Jon Alexander Bender and published by . This book was released on 2020 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: Herein, I showcase three studies that have formed the backbone of my work at UT Austin. First, we studied singlet exciton fission (SF) in a common perylenediimide (PDI) derivative often used as a molecular organic semiconductor, C8-PDI, using pump-probe spectroscopy to model SF and singlet-singlet annihilation (SSA). Therein, we were surprised to report a SF rate orders of magnitude slower than predicted by computational studies of PDI dimers. In Chapter 3, we study a suite of six PDI derivatives that adopt different crystal structures to further assess the nature of SF in polycrystalline films grown on sapphire and fused-quartz. We developed a kinetic model across the PDI series based on the analysis of time-resolved photoluminescence, free from SSA contributions to kinetics that must otherwise be carefully modelled for TA data of these films. We confirm that Redfield theoretic approximations of the SF rate in these materials better captures the trend in kinetics implying the important role the charge-transfer character in these excitons play in mediating the process. The variation in intermolecular organization and associated changes in the Coulombic and exchange coupling between nearest-neighbor molecules correctly captures a qualitative trend in the observed SF rate, though the observed rates are an order of magnitude smaller than expected. We propose this discrepancy arises because the PDI dimer model we use for our predictive model for polycrystalline PDI thin films neglects changes in the excited state character/energetics that become important in strongly interacting molecular solids. The contents of Chapter 4 are then a study of colloidal suspensions of PbS nanocrystals (NC) decorated with a TIPS-pentacene ligand, 2-CP. We set out to search for evidence of the formation of spin-triplet excitons on the 2-CP ligands after photoexcitation of the PbS NC. Triplet exciton formation is observed with no clear observation of an intermediate charge separated species. However, an intermediary state is observed and carefully assigned to a surface associated state on the PbS NC. This hypothesis is further supported by the presence of a multitude of triplet excited states found in constrained DFT computations and fluence dependent pump-probe data providing evidence for the photopassivation the intermediate surface state. In totality, my studies have elucidated excited state dynamics in singlet fission capable polycrystalline films of perylenediimide molecules and contributed to our growing understanding of triplet exciton transfer between PbS NCs and molecular ligands

Download or read book Singlet Exciton Fission in Perylenediimide Thin Films written by Aaron Kristopher Le and published by . This book was released on 2019 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: Singlet exciton fission (SF) is a process where a singlet exciton splits its energy with a neighboring molecule to form two lower energy triplet excitons. This is a process unique to organic molecules, and while intersystem crossing is typically slow in organic molecules due to small spin orbit coupling SF does not require a flip in spin to form these lower energy excitons and can occur on timescales extending from 10s of femtoseconds to nanoseconds. SF becomes efficient when the triplet energy is half of the energy of the singlet energy and occurs on timescales that outcompete deactivation pathways of the singlet exciton such as fluorescence. Efficient SF, or unity singlet to triplet interconversion via SF, has potential applications in improving the efficiencies of photovoltaic devices. Thermalization of high energy excitations in semiconductor photovoltaics pose a major loss channel for device efficiencies. An SF sensitizer can be incorporated into the device to absorb high energy excitations and following down conversion via SF to lower energy excitations thermalization losses can be mitigated. In this work we investigate SF in the perylenediimides (PDIs) in the solid state using ultrafast spectroscopy. The PDIs are deposited as polycrystalline thin films and structurally characterized to determine how the PDIs arrange in the thin films. SF is highly dependent on the intermolecular geometry of the of the participating chromophores, and the PDIs investigated in this work adopt different crystal structures in the solid state. This provides a platform to study the structure-function relationship of intermolecular geometry and SF. SF rates and triplet yield maxima are extracted from time-resolved emission and transient absorption spectroscopy with the aid of a kinetic models. The linear absorption and emission spectra suggest the singlet energy of the polycrystalline PDI films is lower than the monomeric PDIs due to aggregation. The potential disruption to the energetic requirement that the triplet energy be half the singlet would imply SF is an activated process in PDI thin films. We use a combination of temperature dependent time resolved emission and transient absorption spectroscopy to determine SF is endoergic in the PDI studied

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 A Study of the Morphology Dependence of Singlet Fission in Organic Materials Using Magnetic Field Effects and Time Resolved Photoluminescence written by Geoffrey Piland and published by . This book was released on 2016 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: To further enhance photovoltaic efficiencies, singlet fission (SF) has been studied as a possible avenue to exceed the Shockley-Quiesser limit which prohibits single junction solar cells from going beyond 34% efficiency. SF occurs in organic materials when an excited singlet exciton within the organic material splits into two triplet excitons. This process, being spin allowed, occurs rapidly and the resultant triplets have the benefits of longer lifetimes (~ms) and longer diffusion lengths than their singlet counterparts. In order to better utilize this process for applications such as photovoltaics, there must be a better understanding of what systems give rise to high yields of triplets and how to harvest these triplets to do work. This work uses time-resolved fluorescence techniques along with magnetic fields to study how morphology plays a role in the singlet fission process. In order to do this, studies were done on the molecular systems of tetracene, rubrene, and diphenylhexatriene. Expanded versions of the Merrifield kinetic model were created to model the dynamics of these systems and better understand how spin and triplet-triplet annihilation affect the dynamics of the system. We find that amorphous rubrene has a slower singlet fission lifetime than tetracene at 2 ns. Using our expanded model, diphenylhexatriene was found to have a fission lifetime of 290 ps in the monoclinic form while having a 435 ps lifetime in the orthorombic form. Also, differences in fluorescence behavior between thin polycrystalline films and single crystals of tetracene are explored to reduce discrepancies in the literature as to tetracene's singlet fission rate and whether or not its activated by temperature. We find here that single crystal's of tetracene have an average singlet fission lifetime of 170 ps while the polycrystalline films have a lifetime of 70 ps, which we attribute to differences in the number of defects due to grain boundaries and sample preparation. This study also studies the integration of tetracene films with n-type silicon in order to harvest the generated triplets for photovoltaic applications, but evidence was only seen for singlet transfer to the silicon.

Download or read book Emerging Strategies to Reduce Transmission and Thermalization Losses in Solar Cells written by Jonas Sandby Lissau and published by Springer Nature. This book was released on 2021-10-13 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book describes emerging strategies to circumvent transmission and thermalization losses in solar cells, and thereby redefine the limits of solar power conversion efficiency. These strategies include the use of organic molecules and rare-earth metal materials. Approaches to augment the efficiency of these processes via near-field enhancement are described as well. This book includes a discussion of state-of-the-art implementations of these emerging strategies in solar cells, both internally, as in molecular intermediate band and charge carrier multiplication, and externally, such as photon up- and down-conversion. Tools for characterization are also provided. Written by leading researchers in the field, this book can be useful to both beginners and experienced researchers in solar energy.

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 On Exciton Vibration and Exciton Photon Interactions in Organic Semiconductors written by Antonios M. Alvertis and published by Springer Nature. This book was released on 2021-10-25 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: What are the physical mechanisms that underlie the efficient generation and transfer of energy at the nanoscale? Nature seems to know the answer to this question, having optimised the process of photosynthesis in plants over millions of years of evolution. It is conceivable that humans could mimic this process using synthetic materials, and organic semiconductors have attracted a lot of attention in this respect. Once an organic semiconductor absorbs light, bound pairs of electrons with positively charged holes, termed `excitons’, are formed. Excitons behave as fundamental energy carriers, hence understanding the physics behind their efficient generation and transfer is critical to realising the potential of organic semiconductors for light-harvesting and other applications, such as LEDs and transistors. However, this problem is extremely challenging since excitons can interact very strongly with photons. Moreover, simultaneously with the exciton motion, organic molecules can vibrate in hundreds of possible ways, having a very strong effect on energy transfer. The description of these complex phenomena is often beyond the reach of standard quantum mechanical methods which rely on the assumption of weak interactions between excitons, photons and vibrations. In this thesis, Antonios Alvertis addresses this problem through the development and application of a variety of different theoretical methods to the description of these strong interactions, providing pedagogical explanations of the underlying physics. A comprehensive introduction to organic semiconductors is followed by a review of the background theory that is employed to approach the relevant research questions, and the theoretical results are presented in close connection with experiment, yielding valuable insights for experimentalists and theoreticians alike.

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 Radiationless Transitions written by Sheng Lin and published by Elsevier. This book was released on 2012-12-02 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radiationless Transitions is a critical discussion of research studies on the theory and experiments in radiationless transitions. This book is composed of nine chapters, and begins with discussions on the theory and experiment of photophysical processes of single vibronic levels and/or single rovibronic levels. The subsequent chapters deal with the spectroscopic investigations of intramolecular vibrational relaxation; the dynamics of molecular excitation by light; and the photophysical processes of small molecules in condensed phase. The discussions then shift to the high pressure effects on molecular luminescence and the internal conversion involving localized excitations, presenting one qualitative and one quantitative example, as well as the intersystem crossing with localized excitations. A chapter explores the energy transfer processes that occur after a molecule in solution is excited by light, with an emphasis on solid solutions in which the large amplitude molecular motion is largely quenched. This chapter also looks into the liquid solutions in which the molecules can translate and rotate under the influence of fluctuating forces from the liquid. The concluding chapter focuses on ultrafast processes. Researchers in the fields of physics, chemistry, and biology will benefit from this book.

Download or read book Spectroscopic Studies of Singlet Fission and Triplet Excited States in Assemblies of Conjugated Organic Molecules written by Chen Wang and published by . This book was released on 2014 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Triplet states of organic molecules are excited-state species that are important on a fundamental level, as well as for emerging organic electronic devices. The singlet fission mechanism, which generates as many as two triplet excitons per absorbed photon, may improve the efficiency of new OPVs. Singlet fission is a primary focus of this dissertation, particularly the relationship between interchromophore coupling and the yield of triplet excited states. Zeaxanthin, a carotenoid, is a model molecule for this study because it forms aggregates with different interchromophore couplings. Three types of aggregates, as well as zeaxanthin multimers in vesicles, were prepared and probed. The spectroscopic techniques included transient absorption and time-resolved resonance Raman spectroscopy. The coupling strengths between chromophores spanned the range from weak to strong. High yields of triplets by singlet fission were found in all systems with exciton coupling. The most triplets were produced in assemblies with the greatest coupling strength. The results disprove earlier suggestions in the literature that the singlet fission in carotenoids is intramolecular. Our findings also reveal that an optically-allowed S2 state is the parent state for fission, rather than the lowest excited singlet state (S1) as concluded in earlier theoretical work. The first resolved resonance Raman spectra of oligothiophenes in their triplet excited state are also reported and analyzed in this dissertation.

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 Spectroscopic Study of Triplet Exciton Dynamics at the Hybrid Organic inorganic Interface written by Jesse Allardice and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theory of Molecular Excitons written by A. Davydov and published by Springer. This book was released on 2013-11-11 with total page 319 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Resolving Electron Injection from Singlet Fission Borne Triplets into Mesoporous Transparent Conducting Oxides written by and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photoinduced electron transfer from a molecular chromophore into mesoporous metal oxide substrates occurs efficiently from both singlet and triplet excited states for traditional metal-to-ligand charge transfer (MLCT) dyes. All organic molecules that undergo singlet fission (SF), the process of generating two triplet excitons with photoexcitation of one singlet exciton, offers a promising method of generating two charges per one absorbed photon. However, the singlet-triplet energy balance required to drive SF often places the driving force for triplet electron injection into metal oxides too low. As such, the dynamics of singlet vs. triplet electron transfer for SF in dye-sensitized solar cell configurations has not been elucidated. Here, we use applied bias transient absorption spectroscopy to modulate the driving force for triplet electron transfer from an anthradithiophene-based SF chromophore (ADT-COOH) adsorbed to mesoporous indium tin oxide (nanoITO).

Download or read book Photochemistry written by Angelo Albini and published by Springer. This book was released on 2015-10-19 with total page 307 pages. Available in PDF, EPUB and Kindle. Book excerpt: This anthological description of the history and applications of photochemistry provides photochemistry practitioners with complementary information about the field, currently not covered in existing textbooks and handbooks. The first part focuses on the historical development of the field, including light-matter interaction, the discovery of photochemical reactions and the development of modern photochemical mechanisms. This section provides useful background to the second part which outlines applications of photochemistry in the present day, such as in synthesis, green chemistry, diagnostics, medicine and nanotechnology. Furthermore, the author provides an outlook on promising areas for future developments. The broad scope of “Photochemistry: Past, Present and Future” is also of interest to the wider chemical audience and it makes a pleasant read while not compromising on scientific rigor.

Download or read book Coherent Vibrational Dynamics written by Guglielmo Lanzani and published by CRC Press. This book was released on 2007-11-29 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: Remarkable developments in the spectroscopy field regarding ultrashort pulse generation have led to the possibility of producing light pulses ranging from 50 to5 fs and frequency tunable from the near infrared to the ultraviolet range. Such pulses enable us to follow the coupling of vibrational motion to the electronic transitions in molecules and

Download or read book Handbook of Photochemistry written by Marco Montalti and published by CRC Press. This book was released on 2006-02-21 with total page 662 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the publication of the second edition of this handbook in 1993, the field of photochemical sciences has continued to expand across several disciplines including organic, inorganic, physical, analytical, and biological chemistries, and, most recently, nanosciences. Emphasizing the important role light-induced processes play in all of these fie