Optical Properties of Conducting Polymers

Kiess, H.; Harbeke, G.

doi:10.1007/978-3-642-46729-5_4

Cited by 63 publications

(15 citation statements)

References 110 publications

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“…However, ab initio DFT can be unreliable for treating multireference correlation effects, which are important in the excited states of conjugated systems. On the basis of past calculations performed on other polymers such as trans -polyacetylene, it is a well-known fact that to be able to predict the correct excited state orderings in conjugated polymers, it is very important to account for the electron-correlation effects in an accurate manner. Therefore, we decided to go beyond the SCI approach and performed large-scale CI calculations to explore the singlet–triplet ordering in polyacenes.…”

Section: Results and Discussionmentioning

confidence: 99%

Pariser–Parr–Pople Model Based Investigation of Ground and Low-Lying Excited States of Long Acenes

Chakraborty

Shukla

2013

J. Phys. Chem. A

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Several years ago, Angliker et al. [ Chem. Phys. Lett. 1982 , 87 , 208 ] predicted nonacene to be the first linear acene with the triplet state 1(3)B2u as the ground state, instead of the singlet 1(1)Ag state. However, contrary to that prediction, in a recent experimental work, Tönshoff and Bettinger [ Angew. Chem. Int. Ed. 2010 , 49 , 4125 ] demonstrated that nonacene has a singlet ground state. Motivated by this experimental finding, we decided to perform a systematic theoretical investigation of the nature of the ground and the low-lying excited states of long acenes, with an emphasis on the singlet-triplet gap, starting from naphthalene, all the way up to decacene. The methodology adopted in our work is based upon the Pariser-Parr-Pople model (PPP) Hamiltonian, along with the large-scale multireference singles-doubles configuration interaction (MRSDCI) approach. Our results predict that even though the singlet-triplet gap decreases with the increasing conjugation length, nevertheless, it remains finite till decacene, thus providing no evidence of the predicted singlet-triplet crossover. We also analyze the nature of many-particle wave function of the correlated singlet ground state and find that the longer acenes exhibit a tendency toward an open-shell singlet ground state. Moreover, when we compare the experimental absorption spectra of octacene and nonacene with their calculated singlet and triplet absorption spectra, we observe excellent agreement for the singlet case. Hence, the optical absorption results also confirm the singlet nature of the ground state for longer acenes. Calculated triplet absorption spectra of acenes predict two well-separated intense long-axis polarized absorptions, against one such peak observed for the singlet case. This is an important prediction regarding the triplet optics of acenes, which can be tested in future experiments on oriented samples.

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Section: Results and Discussionmentioning

confidence: 99%

Pariser–Parr–Pople Model Based Investigation of Ground and Low-Lying Excited States of Long Acenes

Chakraborty

Shukla

2013

J. Phys. Chem. A

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“…Low quantum efficiencies (QEs) have long been the major hurdle for conjugated polymers (CPs) competing in the field of optoelectronics in spite of their edges in the cost, ease of processing, application flexibility, and mechanical durability. − Recent reports have revealed that increased backbone stresses via mechanical stretching can lead to dramatically enhanced QEs of the CPs in the dispersed solid states. − However, the mechanical effects have been unclear in the pristine counterparts, the prevalent form in applications for CPs, casting doubts on the validity and implications of the mechanical effects. Hence, it is highly intriguing to investigate the mechanical effects thoroughly in the pristine CPs and at the same time, taking advantage of the high chromophore densities in the pristine films, to explore the photonic behavior in the ultrafast time frame commensurate to the electron–phonon coupling that may affect the QE behavior of the long-chain molecules. − …”

Section: Introductionmentioning

confidence: 99%

Quantum Efficiency Increasing of a Pristine Polymer by Curbing Picosecond Self-Trapping via Segmental Stretching

Weng

Chen

et al. 2021

Macromolecules

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The quantum efficiencies of conjugated polymers, which have long been a bottleneck barring their broad optoelectronic applications, are found to be increasing dramatically when the chain-like molecules are stretched into a state of confinement over molecular motions. For pristine MEH-PPV molecules, the stretching-induced confinement becomes effective as the segmental stress (σ) has passed a threshold of ∼100 MPa, overcoming the interventions from molecular aggregates, to cause thereafter an increase of quantum efficiency from 6%, almost linearly with σ, to 55% at σ ∼ 215 MPa. By using ultrafast time-resolved confocal spectroscopy, the efficiency increase is revealed arising from suppression of backbone torsion-mediated self-trapping that is normally occurring within ∼2 picosecond following excitation. The dependence on backbone stresses strongly suggests a significant role of lattice strain energy during photoexcitation, implicating the basic understanding of the energy transformation as well as applications of conjugated polymers.

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“…Since the discovery of the light-emitting polymer, considerable efforts have been made toward understanding its electronic properties. − One of the issues related for these materials in the solid state is the role of interchain interactions. − In general, there are two categories of the interchain effects upon ordered packing of conjugated chains, namely, the morphological change and the formation of the interchain electronic states. The former leads to an increase of conjugation length via improved backbone coplanarity, , whereas the latter causes the delocalization of excitations over different chains; − the latter includes both aggregate and excimer emissions.…”

Section: Introductionmentioning

confidence: 99%

Aggregate versus Excimer Emissions from Poly(2,5-di-n-octyloxy-1,4-phenylenevinylene)

et al. 2007

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Using fractions of poly(2,5-di-n-octyloxy-1,4-phenylenevinylene) (DO-PPV) of different chain lengths, the interchain interactions in both the solution and the bulk states from ambient to cryogenic temperatures were examined via a combination of steady-state and time-resolved photoluminescence spectroscopic techniques. Results indicated that the emission from these aggregates bears characteristics of quantum mechanical dimerization, not that of the extended conjugation of single chains. The emission spectrum from films is generally consistent with the "aggregate emission" spectrum extracted from aggregated solutions; nevertheless, there indeed exists minor emission at the red end of the spectrum, representing contribution from excimers.

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Optical Properties of Conducting Polymers

Cited by 63 publications

References 110 publications

Pariser–Parr–Pople Model Based Investigation of Ground and Low-Lying Excited States of Long Acenes

Pariser–Parr–Pople Model Based Investigation of Ground and Low-Lying Excited States of Long Acenes

Quantum Efficiency Increasing of a Pristine Polymer by Curbing Picosecond Self-Trapping via Segmental Stretching

Aggregate versus Excimer Emissions from Poly(2,5-di-n-octyloxy-1,4-phenylenevinylene)

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