First-Principles Calculations of Pyridines:  From Monomer to Polymer

Vaschetto, Mariana E.; Retamal, B. A.; Monkman, Andrew P.; Springborg, Michael

doi:10.1021/jp992204b

Cited by 22 publications

(18 citation statements)

References 46 publications

(129 reference statements)

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“…Therefore, there is reason to believe that emission in PPY ®lms is possibly predominantly phosphorescence. Furthermore, theoretical calculations of the triplet manifold of PPY [16] yield results in excellent agreement with our radiolysis experiments. Details of the pulse radiolysis measurements of the triplet states in PPY can be found in the paper presented in this conference by Monkman et al [17].…”

supporting

confidence: 81%

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Triplet state dynamics in poly(2,5-pyridine diyl)

et al. 2001

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Pulse radiolysis was used to determine the triplet state energy (2.3 eV) of Poly(2,5-pyridine diyl) (PPY) ®lm which was found to be coincident with the emission energy. Detailed time-resolved photoluminescence (PL) and pump-probe measurements have been applied to study the photoexcited state relaxation dynamics. In ®lms, a very large spectral red-shift ($0.35 eV) for the PL occurred within the ®rst 100 ps whereas no spectral red-shift was observed for the PPY in solution. This result shows clear evidence for the evolution of short-lived singlet emission (S 1 3 S 0 ) at $450 nm to long-lived triplet emission (T 1 3 S 0 ) at $520 nm for the PPY thin ®lm. Streak camera measurement indicates the long live component has a decay time constant of several ns. The picosecond photo-induced triplet state absorption (T 1 3 T 2 transition) peaks at $600 nm as measured by pump-probe which is consistent with both the radiolysis and cw photoinduced absorption measurements. A triplet lifetime of $6 ns is measured which is again consistent with the streak camera measurement. These results lead us to believe that the long live component of the emission from PPY ®lm is in fact phosphorescence. Furthermore, there is evidence that oxygen plays a very important role in the fast triplet radiative lifetime in PPY ®lms. # 2001 Elsevier Science B.V. All rights reserved.Keywords: Poly(2,5-pyridine diyl); Triplet state energy; PPY ®lms; Time-resolved photoluminescence Excited states and their relaxation processes in conjugated polymers have been of signi®cant experimental and theoretical interest in the past decade. With the recent demonstration of polymer light emitting diodes (PLED) [1] and near commercialisation of these devices, a better understanding of the excited state properties of conjugated polymers became even more important. Luminescence in PLED is normally via recombination of singlet excitons. Spin statistics dictate that there is a 3:1 probability of triplet exciton compared to singlet exciton formation from electrical injected charge carrier recombination in PLED, thus a polymer in which ef®cient radiative triplet state recombination can occur will greatly enhance the PLED performance. Indeed a recent realisation of radiative triplet state recombination (i.e. phosphorescence) in organic light emitting device with a quantum ef®cient as high as 7% [2] compared to 3±4% for the singlet exciton emission PLED demonstrated the important role of the triplet state. Therefore, understanding the triplet state manifold and singlet±triplet intersystem crossing for the light emitting polymeric systems are important.The existence of triplet states in conjugated polymers has been well established [3±6]. The photo-induced triplet state absorption (T 1 3 T 2 transition) measurements were the most frequent experimental technique to investigate these triplet states, however, direct triplet exciton emission (i.e. T 1 3 S 0 ) with microsecond lifetime has been observed in poly(3-hexylthiophene) [7] and ladder-type poly(paraphenylene) [8]....

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confidence: 81%

“…This distortion of the ring will enhance mixing of the n and p states, increasing the probability of ISC. Density Functional Theory calculations on the PPY system [16] show that the 3 nÀp Ã triplet state is degenerate in energy with the 1 pÀp Ã , thus this can facilitate resonant (allowed) ISC.…”

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confidence: 99%

Triplet state dynamics in poly(2,5-pyridine diyl)

et al. 2001

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“…where L is the length of polymer, b=4.35 Å (Vaschetto et al, 1999) is the repeat unit length and M 1 its molar mass. N A =6 × 10 22 , α=0.5.…”

Section: Structure In the Solutionmentioning

confidence: 99%

“…The main argument is that d 001 is ca. 4.05 Å instead of the repeat distance of PPY (4.25 Å (Samuelsen et al, 2001) or 4.35 Å (Vaschetto et al, 1999). Therefore, a axis is suggested to be unique and α∼70-85 o .…”

Section: Aligned Self-assembled Structurementioning

confidence: 99%

Diffraction analysis of highly ordered smectic supramolecules of conjugated rodlike polymers

Knaapila¹,

Torkkeli²,

Jokela³

et al. 2003

J Appl Cryst

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A small/wide-angle X-ray scattering and grazing incidence diffraction study of comb-shaped supramolecules of conjugated poly(2,5-pyridinediyl), acid dopant and hydrogen bonded amphiphilic side chains is reported. In solution, polymers are dissolved rodlike particles. When the side-chains are introduced, polymers self-assemble in hierarchic liquid crystals (LC). Diffraction patterns of aligned LC show h00, 020, and 004 reflections, and additional small-angle reflections along the polymer axis. A triangular correlation function indicating a very large correlation length is seen along the smectic axis. An aligned solid structure can be formed by cleaving side chains from the aligned LC.

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“…However, such a high level calculation (including electron correlation with a large basis set) for a polymeric system is still restricted to a small unit system in practice. 18 For relatively large systems, [19][20][21][22][23] polymeric structures have been obtained from the calculations on oligomeric structures or from the experimental measurements. Moreover, it is well known that Hartree-Fock level calculations greatly overestimate the HOMO-LUMO gap of a conjugated polymer.…”

Section: Resultsmentioning

confidence: 99%

Molecular Design of Novel Conjugated Polymers for Blue-Light-Emitting Devices

2003

Bulletin of the Korean Chemical Society

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A quantum-chemical study of conformations and electronic structures of polyheterocyclic derivatives with vinylenediheteroatom substituents at the 3-and 4-positions was performed to search for novel blue-lightemitting conjugated polymers. Conformational potential energy curves of the polymers were constructed as a function of the helical angle (a) through semiempirical Hartree-Fock band calculations at the Austin model 1 level. It is found that poly(3,4-vinylenedioxythiophene) possesses a quite flat curve in the range of α = 51.4 o -120 o . Replacing S atoms for O atoms greatly increases repulsion between the neighboring units, and thereby the units become perpendicular to one another. Because of the hydrogen bonding between O and NH, poly(3,4-vinylenedioxypyrrole) is predicted to be anti-coplanar and poly(3,4-vinylenediaminofuran) to be nearly anticoplanar. According to the modified extended Hückel band calculations, the HOMO-LUMO gaps (HLGs) of the polymers, unless the polymer chains are twisted, are close to or slightly smaller than those of their respective mother polymers. Among the polymers, poly(3,4-vinylenedioxythiophene) is presumed to be the most probable candidate for a blue-light emitter because its HLG is within the range of the electronic requirement for blue-light emitters.

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First-Principles Calculations of Pyridines: From Monomer to Polymer

Cited by 22 publications

References 46 publications

Triplet state dynamics in poly(2,5-pyridine diyl)

Triplet state dynamics in poly(2,5-pyridine diyl)

Diffraction analysis of highly ordered smectic supramolecules of conjugated rodlike polymers

Molecular Design of Novel Conjugated Polymers for Blue-Light-Emitting Devices

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