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Journal ArticleDOI

Triplet states in a series of Pt-containing ethynylenes

19 Oct 2000-Journal of Chemical Physics (American Institute of Physics Publising LLC)-Vol. 113, Iss: 17, pp 7627-7634
TL;DR: In this paper, the authors studied the evolution of the triplet excited state in a series of six ethynylenic polymers, where the spacer unit R was systematically varied to give optical gaps from 1.7 − 3.0 eV.
Abstract: By use of optical steady state and time resolved spectroscopy, we studied the evolution of the triplet excited state in a series of six ethynylenic polymers of the structure [-Pt(PBu3n)2-C≡C-R-C≡C-]n where the spacer unit R is systematically varied to give optical gaps from 1.7–3.0 eV. The inclusion of platinum in the polymer backbone induces a strong spin-orbit coupling such that triplet state emission (phosphorescence) associated with the conjugated system can be detected. Throughout the series we find the S1-T1 (singlet-triplet) energy splitting to be independent of the spacer R, such that the T1 state is always 0.7±0.1 eV below the S1 state. With decreasing optical gap, the intensity and lifetime of the triplet state emission were seen to reduce in accordance with the energy gap law.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors provide an overview of some of the strategies for maximising the luminescence efficiencies of simple square-planar platinum(II) complexes in solution, including the introduction of strong-field co-ligands into di- and tri-imine complexes, involvement of intraligand charge-transfer excited states, and cyclometallation.

493 citations

Journal ArticleDOI
TL;DR: In this article, a review on the photophysical processes associated with the formation of triplet states and their decay, as well as the energy levels and energy transfer processes of the triplet spin states are presented.
Abstract: Today's technology is not possible without optoelectronic devices such as light-emitting diodes, transistors and solar cells. These basic units of modern electronic appliances may be made not only from traditional inorganic semiconductors, but also from organic semiconductors, i.e. hydrocarbon molecules that combine semiconducting properties with some mechanical properties such as easy processability and flexibility. The weak van der Waals forces that bind the molecules to a solid imply a low dielectric constant, so that coulomb and exchange interactions between electrons are significant. As a result, photoexcitation or electrical excitation results in strongly bound electron–hole pairs, so-called excitons. Depending on the relative orientation of the electron and hole spin, the exciton may be of a overall singlet or triplet spin state. While the fluorescent singlet state has been investigated intensively since the first reports of organic electroluminescence, research into the properties of the phosphorescent triplet state has intensified mainly during the last decade. In this review we give an overview on the photophysical processes associated with the formation of triplet states and their decay, as well as the energy levels and energy transfer processes of triplet states. We aim to give a careful introduction for those new to this particular research area as well as to highlight some of the current research issues and intriguing questions for those familiar with the field. The main focus of this review is on molecular assemblies and polymer films, though relevant work on molecular crystals is also included where it assists in forming a larger picture.

471 citations

Journal ArticleDOI
25 Oct 2001-Nature
TL;DR: It is suggested that a spin-dependent process, favouring singlet formation, is effective in the polymer, and that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius.
Abstract: The efficiency of light-emitting diodes (LEDs) made from organic semiconductors is determined by the fraction of injected electrons and holes that recombine to form emissive spin-singlet states rather than non-emissive spin-triplet states. If the process by which these states form is spin-independent, the maximum efficiency of organic LEDs will be limited to 25 per cent1. But recent reports have indicated fractions of emissive singlet states ranging from 22 to 63 per cent2,3,4,5, and the reason for this variation remains unclear. Here we determine the absolute fraction of singlet states generated in a platinum-containing conjugated polymer and its corresponding monomer. The spin-orbit coupling introduced by the platinum atom allows triplet-state emission, so optically and electrically generated luminescence from both singlet and triplet states can be compared directly. We find an average singlet generation fraction of 22 ± 1 per cent for the monomer, but 57 ± 4 per cent for the polymer. This suggests that recombination is spin-independent for the monomer, but that a spin-dependent process, favouring singlet formation, is effective in the polymer. We suggest that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius.

444 citations

Journal ArticleDOI
TL;DR: It is found that the nonradiative decay rate from the triplet state T(1) increases exponentially with decreasing T( 1)-S(0) gap for the polymers and monomers at 300 and 20 K.
Abstract: The energy gap law established for aromatic hydrocarbons and rare earth ions relates the nonradiative decay rate to the energy gap of a transition through a multiphonon emission process. We show that this energy gap law can be applied to the phosphoresce of a series of conjugated polymers and monomers for which the radiative decay rate has been enhanced through incorporation of a heavy metal. We find that the nonradiative decay rate from the triplet state T(1) increases exponentially with decreasing T(1)-S(0) gap for the polymers and monomers at 300 and 20 K. Comparison of the nonradiative decay of polymers with that of their corresponding monomers highlights the role of electron-lattice coupling.

430 citations

Journal ArticleDOI
TL;DR: The synthesis and photophysical and electroluminescent properties for a series of platinum(II) alpha-diimine bis(arylacetylide) complexes and the impact of different solvents, substituents on the diimine ligands, and complex concentrations upon their emissive behavior have been examined and demonstrates that their emission energies can be systematically modified.
Abstract: We present the synthesis and photophysical and electroluminescent properties for a series of platinum(II) alpha-diimine bis(arylacetylide) complexes. The molecular structures of five derivatives have been elucidated by X-ray crystallography. Intermolecular pi-pi interactions (between aromatic diimine and phenylacetylide moieties) are apparent in the crystal lattices of two of these. All bis(phenylacetylide) derivatives exhibit intense triplet metal-to-ligand charge transfer (MLCT) photoluminescence in the solid state and in fluid solutions at room temperature. The impact of different solvents, substituents on the diimine ligands, and complex concentrations upon their emissive behavior have been examined and demonstrates that their emission energies can be systematically modified. Application of the 3MLCT excited state of the [Pt(alpha-diimine) (C(triple bond)CPh)2] materials in single- and double-layer organic light-emitting devices are described. The bis(butadiynyl) complex [Pt(4,4'-dtbpy)(C(triple bond)C-C(triple bond)CPh)2] (dtbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) displays strong solid-state and solution phosphorescence at 77 and 298 K; the associated excited state is proposed to arise from both acetylenic 3pi pi*(C(triple bond)C-C(triple bond)CPh) and 3MLCT [Pt --> pi*(diimine)] transitions.

327 citations

References
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Journal ArticleDOI
10 Sep 1998-Nature
TL;DR: In this article, a host material doped with the phosphorescent dye PtOEP (PtOEP II) was used to achieve high energy transfer from both singlet and triplet states.
Abstract: The efficiency of electroluminescent organic light-emitting devices1,2 can be improved by the introduction3 of a fluorescent dye. Energy transfer from the host to the dye occurs via excitons, but only the singlet spin states induce fluorescent emission; these represent a small fraction (about 25%) of the total excited-state population (the remainder are triplet states). Phosphorescent dyes, however, offer a means of achieving improved light-emission efficiencies, as emission may result from both singlet and triplet states. Here we report high-efficiency (≳90%) energy transfer from both singlet and triplet states, in a host material doped with the phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) (PtOEP). Our doped electroluminescent devices generate saturated red emission with peak external and internal quantum efficiencies of 4% and 23%, respectively. The luminescent efficiencies attainable with phosphorescent dyes may lead to new applications for organic materials. Moreover, our work establishes the utility of PtOEP as a probe of triplet behaviour and energy transfer in organic solid-state systems.

7,023 citations

Book
01 Jan 1986
TL;DR: In this paper, the authors presented the theory and properties of conjugated polymers, including transport, optical, and self-assembly properties of poly(3,4-Ethylenedioxythiophene)-polymers.
Abstract: Volume 1: Conjugated Polymers: Theory, Synthesis, Properties, and Characterization PART 1: THEORY OF CONJUGATED POLYMERS On the Transport, Optical, and Self-Assembly Properties of -Conjugated Materials: A Combined Theoretical/Experimental Insight D. Beljonne, J. Cornil, V. Coropceanu, D.A. da Silva Filho, V. Geskin, R. Lazzaroni, P. Leclere, and J.-L. Bredas Theoretical Studies of Electron-Lattice Dynamics in Organic Systems S. Stafstroem PART 2: SYNTHESIS AND CLASSES OF CONJUGATED POLYMERS Helical Polyacetylene Synthesized in Chiral Nematic Liquid Crystals K. Akagi Synthesis and Properties of Poly(arylene vinylene)s A.C. Grimsdale and A.B. Holmes Blue-Emitting Poly(para-Phenylene)-Type Polymers E.J.W. List and U. Scherf Poly(paraPhenyleneethynylene)s and Poly(aryleneethynylene)s: Materials with a Bright Future U.H.F. Bunz Polyaniline Nanofibers: Synthesis, Properties, and Applications J. Huang and R.B. Kaner Recent Advances in Polypyrrole S.H. Cho, K.T. Song, and J.Y. Lee Regioregular Polythiophenes M. Jeffries-El and R.D. McCullough Poly(3,4-Ethylenedioxythiophene)-Scientific Importance, Remarkable Properties, and Applications S. Kirchmeyer, K. Reuter, and J.C. Simpson Thienothiophenes: From Monomers to Polymers G.A. Sotzing, V. Seshadri, and F.J. Waller Low Bandgap Conducting Polymers S.C. Rasmussen and M. Pomerantz Advanced Functional Polythiophenes Based on Tailored Precursors P. Blanchard, P. Leriche, P. Frere, and J. Roncali Structure-Property Relationships and Applications of Conjugated Polyelectrolytes K.S. Schanze and X. Zhao PART 3: PROPERTIES AND CHARACTERIZATION OF CONJUGATED POLYMERS Insulator-Metal Transition and Metallic State in Conducting Polymers A.J. Epstein One-Dimensional Charge Transport in Conducting Polymer Nanofibers A.N. Aleshin and Y.W. Park Structure Studies of - and - Conjugated Polymers M.J. Winokur Electrochemistry of Conducting Polymers P. Audebert and F. Miomandre Internal Fields and Electrode Interfaces in Organic Semiconductor Devices: Noninvasive Investigations via Electroabsorption T.M. Brown and F. Cacialli Electrochromism of Conjugated Conducting Polymers A.L. Dyer and J.R. Reynolds Photoelectron Spectroscopy of Conjugated Polymers M.P. de Jong, G. Greczyniski, W. Osikowicz, R. Friedlein, X. Crispin, M. Fahlman, and W.R. Salaneck Ultrafast Exciton Dynamics and Laser Action in -ConjugatedSemiconductors Z. Valy Vardeny and O. Korovyanko Volume 2: Conjugated Polymers: Processing and Applications PART 1: PROCESSING OF CONJUGATED POLYMERS Conductive Polymers as Organic Nanometals B. Wessling Conducting Polymer Fiber Production and Applications I.D. Norris and B.R. Mattes Inkjet Printing and Patterning of PEDOT-PSS: Application to Optoelectronic Devices Y. Yoshioka and G.E. Jabbour Printing Organic Electronics on Flexible Substrates N.D. Robinson and M. Berggren PART 2: APPLICATIONS AND DEVICES BASED ON CONJUGATED POLYMERS Polymers for Use in Polymeric Light-Emitting Diodes: Structure-Property Relationships H. Christian-Pandya, S. Vaidyanathan, and M. Galvin Organic Electro-Optic Materials L.R. Dalton Conjugated Polymer Electronics-Engineering Materials and Devices N. Tessler, J. Veres, O. Globerman, N. Rappaport, Y. Preezant, Y. Roichman, O. Solomesch, S. Tal, E. Gershman, M. Adler, V. Zolotarev, V. Gorelik, and Y. Eichen Electrical Bistable Polymer Films and Their Applications in Memory Devices J. Ouyang, C.-W. Chu, R.J. Tseng, A. Prakash, and Y. Yang Electroactive Polymers for Batteries and Supercapacitors J.A. Irvin, D.J. Irvin, and J.D. Stenger-Smith Conjugated Polymer-Based Photovoltaic Devices A.J. Mozer and N.S. Sariciftci Biomedical Applications of Inherently Conducting Polymers (ICPs),P.C. Innis, S.E. Moulton, and G.G. Wallace Biosensors Based on Conducting Electroactive Polymers S. Brahim, A.M. Wilson, and A. Guiseppi-Elie Optical Biosensors Based on Conjugated Polymers K. Peter, R. Nilsson, and O. Inganas Conjugated Polymers for Microelectromechanical and Other Microdevices G.M. Spinks and E. Smela Corrosion Protection Using Conducting Polymers D.E. Tallman and G.P. Bierwagen Artificial Muscles T.F. Otero

5,843 citations

Journal ArticleDOI
TL;DR: In this article, a unified treatment of non-radiative decay processes in large molecules which involve either electronic relaxation between two electronic states or unimolecular rearrangeme(s) is presented.
Abstract: In this paper we present a unified treatment of non-radiative decay processes in large molecules which involve either electronic relaxation between two electronic states or unimolecular rearrangeme...

2,060 citations

Journal ArticleDOI
17 Feb 2000-Nature
TL;DR: This work uses the mechanism for energetic coupling between phosphorescent and fluorescent molecular species is a long-range, non-radiative energy transfer: the internal efficiency of fluorescence can be as high as 100%.
Abstract: To obtain the maximum luminous efficiency from an organic material, it is necessary to harness both the spin-symmetric and anti-symmetric molecular excitations (bound electron-hole pairs, or excitons) that result from electrical pumping This is possible if the material is phosphorescent, and high efficiencies have been observed in phosphorescent organic light-emitting devices However, phosphorescence in organic molecules is rare at room temperature The alternative radiative process of fluorescence is more common, but it is approximately 75% less efficient, due to the requirement of spin-symmetry conservation Here, we demonstrate that this deficiency can be overcome by using a phosphorescent sensitizer to excite a fluorescent dye The mechanism for energetic coupling between phosphorescent and fluorescent molecular species is a long-range, non-radiative energy transfer: the internal efficiency of fluorescence can be as high as 100% As an example, we use this approach to nearly quadruple the efficiency of a fluorescent red organic light-emitting device

2,050 citations

Journal ArticleDOI
TL;DR: In this paper, a technique is presented to determine the spin statistics of excitons formed by electrical injection in a semiconducting organic thin film with the aid of selective addition of luminescent dyes.
Abstract: A technique is presented to determine the spin statistics of excitons formed by electrical injection in a semiconducting organic thin film. With the aid of selective addition of luminescent dyes, we generate either fluorescence or phosphorescence from the archetype organic host material aluminum tris (8-hydroxyquinoline) $({\mathrm{Alq}}_{3}).$ Spin statistics are calculated from the ratio of fluorescence to phosphorescence in the films under electrical excitation. After accounting for varying photoluminescent efficiencies, we find a singlet fraction of excitons in ${\mathrm{Alq}}_{3}$ of $(22\ifmmode\pm\else\textpm\fi{}3)%.$

1,004 citations