1
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Fureraj I, Wega J, Balanikas E, Puji Pamungkas KK, Sakai N, Matile S, Vauthey E. Excitation-Wavelength-Dependent Photophysics of a Torsionally Disordered Push-Pull Dye. J Phys Chem Lett 2024:7857-7862. [PMID: 39052969 DOI: 10.1021/acs.jpclett.4c01840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/27/2024]
Abstract
The torsional disorder of conjugated dyes in the electronic ground state can lead to inhomogeneous broadening of the S1 ←S0 absorption band, allowing for the selective photoexcitation of molecules with different amounts of distortion. Here, we investigate how this affects electronic transitions to upper excited states. We show that torsion of a core-alkynylated push-pull dye can have opposite effects on the oscillator strength of its lowest-energy transitions. Consequently, photoselection of planar and twisted molecules can be achieved by exciting in distinct absorption bands. Whereas this has limited effect in liquids due to fast planarization of the excited molecules, it strongly affects the overall photophysics in a polymeric environment, where torsional motion is hindered, allowing for the photoselection of molecules with different fluorescence quantum yields and intersystem-crossing dynamics.
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Affiliation(s)
- Ina Fureraj
- Department of Physical Chemistry, University of Geneva, CH-1211 Geneva, Switzerland
| | - Johannes Wega
- Department of Physical Chemistry, University of Geneva, CH-1211 Geneva, Switzerland
| | - Evangelos Balanikas
- Department of Physical Chemistry, University of Geneva, CH-1211 Geneva, Switzerland
| | | | - Naomi Sakai
- Department of Organic Chemistry, University of Geneva, CH-1211 Geneva, Switzerland
| | - Stefan Matile
- Department of Organic Chemistry, University of Geneva, CH-1211 Geneva, Switzerland
| | - Eric Vauthey
- Department of Physical Chemistry, University of Geneva, CH-1211 Geneva, Switzerland
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2
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Sowa JK, Allen TC, Rossky PJ. Accumulation and ordering of P3HT oligomers at the liquid-vapor interface with implications for thin-film morphology. Phys Chem Chem Phys 2023; 25:20808-20816. [PMID: 37493614 DOI: 10.1039/d3cp02718j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/27/2023]
Abstract
The morphology of semiconducting polymer thin films is known to have a profound effect on their opto-electronic properties. Although considerable efforts have been made to control and understand the processes which influence the structures of these systems, it remains largely unclear what physical factors determine the arrangement of polymer chains in spin-cast films. Here, we investigate the role that the liquid-vapor interfaces in chlorobenzene solutions of poly(3-hexylthiophene) [P3HT] play in the conformational geometries adopted by the polymers. Using all-atom molecular dynamics (MD), and supported by toy-model simulations, we demonstrate that, with increasing concentration, P3HT oligomers in solution exhibit a strong propensity for the liquid-vapor interface. Due to the differential solubility of the backbone and side chains of the oligomers, in the vicinity of this interface, hexyl chains and the thiophene rings, have a clear orientational preference with respect to the liquid surface. At high concentrations, we additionally establish a substantial degree of inter-oligomer alignment and thiophene ring stacking near the interface. Our results broadly concur with the limited existing experimental evidence and we suggest that the interfacial structure can act as a template for film structure. We argue that the differences in solvent affinity of the side chain and backbone moieties are the driving force for the anisotropic orientations of the polymers near the interface. This finer grained description contrasts with the usual monolithic characterization of polymer units. Since this phenomenon can be controlled by concurrent chemical design and the choice of solvents, this work establishes a fabrication principle which may be useful to develop more highly functional polymer films.
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Affiliation(s)
- Jakub K Sowa
- Department of Chemistry, Rice University, Houston, TX 77005, USA.
| | - Thomas C Allen
- Department of Chemistry, Rice University, Houston, TX 77005, USA.
| | - Peter J Rossky
- Department of Chemistry, Rice University, Houston, TX 77005, USA.
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3
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Palacino-González E, Jansen TLC. Modeling the Effect of Disorder in the Two-Dimensional Electronic Spectroscopy of Poly-3-hexyltiophene in an Organic Photovoltaic Blend: A Combined Quantum/Classical Approach. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2023; 127:6793-6801. [PMID: 37081993 PMCID: PMC10108354 DOI: 10.1021/acs.jpcc.3c01080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 02/28/2023] [Indexed: 05/03/2023]
Abstract
We introduce a first-principles model of the 12-mer poly-3-hexyltiophene (P3HT) polymer system in the realistic description of an organic photovoltaic blend environment. We combine Molecular Dynamics (MD) simulations of a thin-film blend of P3HT and phenyl-C61-butyric acid methyl ester (PCBM) to model the interactions with a fluctuating environment with Time-Dependent Density Functional Theory (TDDFT) calculations to parametrize the effect of the torsional flexibility in the polymer and construct an exciton-type Hamiltonian that describes the photoexcitation of the polymer. This allows us to reveal the presence of different flexibility patterns governed by the torsional angles along the polymer chain which, in the interacting fluctuating environment, control the broadening of the spectral observables. We identify the origin of the homogeneous and inhomogeneous line shape of the simulated optical signals. This is paramount to decipher the spectroscopic nature of the ultrafast electron-transfer process occurring in organic photovoltaic (OPV) materials.
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4
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Eder T, Kraus D, Höger S, Vogelsang J, Lupton JM. Vibrations Responsible for Luminescence from HJ-Aggregates of Conjugated Polymers Identified by Cryogenic Spectroscopy of Single Nanoparticles. ACS NANO 2022; 16:6382-6393. [PMID: 35394735 DOI: 10.1021/acsnano.2c00472] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
A single polymer chain can be thought of as a covalently bound J-aggregate, where the microscopic transition-dipole moments line up to emit in phase. Packing polymer chains into a bulk film can result in the opposite effect, inducing H-type coupling between chains. Cofacial transition-dipole moments oscillate out of phase, canceling each other out, so that the lowest-energy excited state turns dark. H-aggregates of conjugated polymers can, in principle, be coaxed into emitting light by mixing purely electronic and vibronic transitions. However, it is challenging to characterize this electron-phonon coupling experimentally. In a bulk film, many different conformations exist with varying degrees of intrachain J-type and interchain H-type coupling strengths, giving rise to broad and featureless aggregate absorption and emission spectra. Even if single nanoparticles consisting of only a few single chains are grown in a controlled fashion, the luminescence spectra remain broad, owing to the underlying molecular dynamics and structural heterogeneity at room temperature. At cryogenic temperatures, emission from H-type aggregates should be suppressed because, in the absence of thermal energy, internal conversion drives the aggregate to the lowest-energy dark state. At the same time, electronic and vibronic transitions narrow substantially, facilitating the attribution of spectral signatures to distinct vibrational modes. We demonstrate how to distinguish signatures of interchain H-type aggregate species from those of intramolecular J-type coupling. Whereas all dominant vibronic modes revealed in the photoluminescence (PL) and surface-enhanced resonance Raman scattering spectra of a single chromophore within a single polymer chain are identified in the J-type aggregate luminescence spectra, they are not all present at once in the H-type spectra. Universal spectral features are found for the luminescence from strongly HJ-coupled chains, clearly resolving the vibrations responsible for the nonadiabatic excited-state molecular dynamics that enable light emission. We discuss the possible combinations of vibrational modes responsible for H-type aggregate PL and demonstrate that only one, mainly the lowest energy one, of the three dominant vibrational modes contributes to the 0-1 transition, whereas combinations of all three are found in the 0-2 transition. From this analysis, we can distinguish between energy shifts due to either J-type intrachain coupling or H-type interchain interactions, offering a means to directly discriminate between structural and energetic disorder.
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Affiliation(s)
- Theresa Eder
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany
| | - Daniel Kraus
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany
| | - Sigurd Höger
- Kekulé-Institut für Organische Chemie und Biochemie der Universität Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
| | - Jan Vogelsang
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany
| | - John M Lupton
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany
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5
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Friday DM, Jackson NE. Modeling the Interplay of Conformational and Electronic Structure in Conjugated Polyelectrolytes. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c00007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- David M. Friday
- Department of Chemistry, University of Illinois at Urbana−Champaign, 505 S Mathews Avenue, Urbana, Illinois 61801, United States
| | - Nicholas E. Jackson
- Department of Chemistry, University of Illinois at Urbana−Champaign, 505 S Mathews Avenue, Urbana, Illinois 61801, United States
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6
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Garzón-Ramírez AJ, Gastellu N, Simine L. Optoelectronic Current through Unbiased Monolayer Amorphous Carbon Nanojunctions. J Phys Chem Lett 2022; 13:1057-1062. [PMID: 35077187 DOI: 10.1021/acs.jpclett.1c03981] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Monolayer amorphous carbon (MAC) is a recently synthesized disordered 2D carbon material. An ensemble of MAC nanofragments contains diverse manifestations of lattice disorder, and because of disorder the key unifying characteristic of this ensemble is poor electronic conductance. Curiously, our computational analysis of the electronic properties of MAC nanofragments revealed an additional commonality: a robust presence of charge-transfer character for electronic transitions from the occupied to virtual orbitals. This charge-transfer property suggests possible applications in optoelectronics. In this Letter, we demonstrate computationally that a laser pulse induces directional electronic currents in unbiased MAC nanojunctions and discuss the effects of pulse intensity on the magnitude of electron transfer.
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Affiliation(s)
| | - Nicolas Gastellu
- Department of Chemistry, McGill University, Montreal, Quebec H3A 0B8, Canada
| | - Lena Simine
- Department of Chemistry, McGill University, Montreal, Quebec H3A 0B8, Canada
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7
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Nguyen D, Tao L, Li Y. Integration of Machine Learning and Coarse-Grained Molecular Simulations for Polymer Materials: Physical Understandings and Molecular Design. Front Chem 2022; 9:820417. [PMID: 35141207 PMCID: PMC8819075 DOI: 10.3389/fchem.2021.820417] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Accepted: 12/31/2021] [Indexed: 12/21/2022] Open
Abstract
In recent years, the synthesis of monomer sequence-defined polymers has expanded into broad-spectrum applications in biomedical, chemical, and materials science fields. Pursuing the characterization and inverse design of these polymer systems requires our fundamental understanding not only at the individual monomer level, but also considering the chain scales, such as polymer configuration, self-assembly, and phase separation. However, our accessibility to this field is still rudimentary due to the limitations of traditional design approaches, the complexity of chemical space along with the burdened cost and time issues that prevent us from unveiling the underlying monomer sequence-structure-property relationships. Fortunately, thanks to the recent advancements in molecular dynamics simulations and machine learning (ML) algorithms, the bottlenecks in the tasks of establishing the structure-function correlation of the polymer chains can be overcome. In this review, we will discuss the applications of the integration between ML techniques and coarse-grained molecular dynamics (CGMD) simulations to solve the current issues in polymer science at the chain level. In particular, we focus on the case studies in three important topics—polymeric configuration characterization, feed-forward property prediction, and inverse design—in which CGMD simulations are leveraged to generate training datasets to develop ML-based surrogate models for specific polymer systems and designs. By doing so, this computational hybridization allows us to well establish the monomer sequence-functional behavior relationship of the polymers as well as guide us toward the best polymer chain candidates for the inverse design in undiscovered chemical space with reasonable computational cost and time. Even though there are still limitations and challenges ahead in this field, we finally conclude that this CGMD/ML integration is very promising, not only in the attempt of bridging the monomeric and macroscopic characterizations of polymer materials, but also enabling further tailored designs for sequence-specific polymers with superior properties in many practical applications.
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Affiliation(s)
- Danh Nguyen
- Department of Mechanical Engineering, University of Connecticut, Mansfield, CT, United States
| | - Lei Tao
- Department of Mechanical Engineering, University of Connecticut, Mansfield, CT, United States
| | - Ying Li
- Department of Mechanical Engineering, University of Connecticut, Mansfield, CT, United States
- Polymer Program, Institute of Materials Science, University of Connecticut, Mansfield, CT, United States
- *Correspondence: Ying Li,
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8
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Gastellu N, Kilgour M, Simine L. Electronic Conduction through Monolayer Amorphous Carbon Nanojunctions. J Phys Chem Lett 2022; 13:339-344. [PMID: 35021673 DOI: 10.1021/acs.jpclett.1c03769] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
In molecular electronic conduction, exotic lattice morphologies often give rise to exotic behaviors. Among 2D systems, graphene is a notable example. Recently, a stable amorphous version of graphene called monolayer amorphous carbon (MAC) was synthesized. MAC poses a new set of questions regarding the effects of disorder on conduction. In this Letter, we perform an ensemble-level computational analysis of the coherent electronic transmission through MAC nanofragments in search of defining characteristics. Our analysis, relying on a semiempirical Hamiltonian (Pariser-Parr-Pople) and Landauer theory, showed that states near the Fermi energy (EF) in MAC inherit partial characteristics of analogous surface states in graphene nanofragments. Away from EF, current is carried by a set of delocalized states that transition into a subset of insulating interior states at the extreme portions of MAC's energy spectrum. Finally, we also found that quantum interference between frontier orbitals is a common feature among MAC nanofragments.
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Affiliation(s)
- Nicolas Gastellu
- Department of Chemistry, McGill University, Montreal, Quebec H3A 0B8, Canada
| | - Michael Kilgour
- Department of Chemistry, McGill University, Montreal, Quebec H3A 0B8, Canada
| | - Lena Simine
- Department of Chemistry, McGill University, Montreal, Quebec H3A 0B8, Canada
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9
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Brey D, Binder R, Martinazzo R, Burghardt I. Signatures of coherent vibronic exciton dynamics and conformational control in two-dimensional electronic spectroscopy of conjugated polymers. Faraday Discuss 2022; 237:148-167. [DOI: 10.1039/d2fd00014h] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two-dimensional electronic spectroscopy (2DES) signals for homo-oligomer J-aggregates are computed, with a focus on the role of structural change induced by low-frequency torsional modes along with quasi-stationary trapping effects induced...
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10
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Beer P, Reichstein PM, Schötz K, Raithel D, Thelakkat M, Köhler J, Panzer F, Hildner R. Disorder in P3HT Nanoparticles Probed by Optical Spectroscopy on P3HT- b-PEG Micelles. J Phys Chem A 2021; 125:10165-10173. [PMID: 34797986 PMCID: PMC8647091 DOI: 10.1021/acs.jpca.1c08377] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We employ photoluminescence (PL) spectroscopy on individual nanoscale aggregates of the conjugated polymer poly(3-hexylthiophene), P3HT, at room temperature (RT) and at low temperature (LT) (1.5 K), to unravel different levels of structural and electronic disorder within P3HT nanoparticles. The aggregates are prepared by self-assembly of the block copolymer P3HT-block-poly(ethylene glycol) (P3HT-b-PEG) into micelles, with the P3HT aggregates constituting the micelles' core. Irrespective of temperature, we find from the intensity ratio between the 0-1 and 0-0 peaks in the PL spectra that the P3HT aggregates are of H-type nature, as expected from π-stacked conjugated thiophene backbones. Moreover, the distributions of the PL peak ratios demonstrate a large variation of disorder between micelles (inter-aggregate disorder) and within individual aggregates (intra-aggregate disorder). Upon cooling from RT to LT, the PL spectra red-shift by 550 cm-1, and the energy of the (effective) carbon-bond stretch mode is reduced by 100 cm-1. These spectral changes indicate that the P3HT backbone in the P3HT-b-PEG copolymer does not fully planarize before aggregation at RT and that upon cooling, partial planarization occurs. This intra-chain torsional disorder is ultimately responsible for the intra- and inter-aggregate disorder. These findings are supported by temperature-dependent absorption spectra on thin P3HT films. The interplay between intra-chain, intra-aggregate, and inter-aggregate disorder is key for the bulk photophysical properties of nanoparticles based on conjugated polymers, for example, in hierarchical (super-) structures. Ultimately, these properties determine the usefulness of such structures in hybrid organic-inorganic materials, for example, in (bio-)sensing and optoelectronics applications.
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Affiliation(s)
- Patrick Beer
- Spectroscopy of Soft Matter, University of Bayreuth, 95440 Bayreuth, Germany
| | - Paul M Reichstein
- Applied Functional Polymers, University of Bayreuth, 95440 Bayreuth, Germany
| | - Konstantin Schötz
- Soft Matter Optoelectronics, University of Bayreuth, 95440 Bayreuth, Germany
| | - Dominic Raithel
- Spectroscopy of Soft Matter, University of Bayreuth, 95440 Bayreuth, Germany
| | - Mukundan Thelakkat
- Applied Functional Polymers, University of Bayreuth, 95440 Bayreuth, Germany.,Bavarian Polymer Institute, University of Bayreuth, 95440 Bayreuth, Germany.,Bayreuther Institut für Makromolekülforschung (BIMF), University of Bayreuth, 95440 Bayreuth, Germany
| | - Jürgen Köhler
- Spectroscopy of Soft Matter, University of Bayreuth, 95440 Bayreuth, Germany.,Bavarian Polymer Institute, University of Bayreuth, 95440 Bayreuth, Germany.,Bayreuther Institut für Makromolekülforschung (BIMF), University of Bayreuth, 95440 Bayreuth, Germany
| | - Fabian Panzer
- Soft Matter Optoelectronics, University of Bayreuth, 95440 Bayreuth, Germany
| | - Richard Hildner
- Spectroscopy of Soft Matter, University of Bayreuth, 95440 Bayreuth, Germany.,Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
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11
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Armstrong ZT, Kunz MB, Zanni MT. Ultrafast Fluctuations in PM6 Domains of Binary and Ternary Organic Photovoltaic Thin Films Probed with Two-Dimensional White-Light Spectroscopy. J Phys Chem Lett 2021; 12:8972-8979. [PMID: 34506148 DOI: 10.1021/acs.jpclett.1c02234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We present two-dimensional white-light spectroscopy (2DWL) measurements of binary and ternary bulk heterojunctions of the polymer donor PM6 mixed with state-of-the-art nonfullerene acceptors Y6 or IT4F. The ternary film has a shorter lifetime and faster spectral diffusion than either of the binary films. 2D line shape analysis of the PM6 ground state bleach with a Kubo model determines that all three films have similar amplitudes of fluctuations (Δ = 0.29 fs-1) in their transition frequencies, but different relaxation times (ranging from 102 to 24 fs). The ternary film exhibits faster dynamics than either of the binary films. The short lifetime of the ternary blend is consistent with increased photoexcitation transfer and the fast frequency fluctuations are consistent with structural dynamics of aliphatic side chains. These results suggest that the femtosecond fluctuations of PM6 are impacted by the choice of the acceptor molecules. We hypothesize that those dynamics are either indicative, or perhaps the initial source, of structural dynamics that ultimately contribute to solar cell operation.
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Affiliation(s)
- Zachary T Armstrong
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Miriam Bohlmann Kunz
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Martin T Zanni
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
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12
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Lee CK, Lu C, Yu Y, Sun Q, Hsieh CY, Zhang S, Liu Q, Shi L. Transfer learning with graph neural networks for optoelectronic properties of conjugated oligomers. J Chem Phys 2021; 154:024906. [PMID: 33445906 DOI: 10.1063/5.0037863] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Despite the remarkable progress of machine learning (ML) techniques in chemistry, modeling the optoelectronic properties of long conjugated oligomers and polymers with ML remains challenging due to the difficulty in obtaining sufficient training data. Here, we use transfer learning to address the data scarcity issue by pre-training graph neural networks using data from short oligomers. With only a few hundred training data, we are able to achieve an average error of about 0.1 eV for the excited-state energy of oligothiophenes against time-dependent density functional theory (TDDFT) calculations. We show that the success of our transfer learning approach relies on the relative locality of low-lying electronic excitations in long conjugated oligomers. Finally, we demonstrate the transferability of our approach by modeling the lowest-lying excited-state energies of poly(3-hexylthiophene) in its single-crystal and solution phases using the transfer learning models trained with the data of gas-phase oligothiophenes. The transfer learning predicted excited-state energy distributions agree quantitatively with TDDFT calculations and capture some important qualitative features observed in experimental absorption spectra.
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Affiliation(s)
| | - Chengqiang Lu
- Anhui Province Key Lab of Big Data Analysis and Application, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yue Yu
- Chemistry and Chemical Biology, University of California, Merced, California 95343, USA
| | - Qiming Sun
- Tencent America, Palo Alto, California 94306, USA
| | | | | | - Qi Liu
- Anhui Province Key Lab of Big Data Analysis and Application, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Liang Shi
- Chemistry and Chemical Biology, University of California, Merced, California 95343, USA
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13
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Ghosh A, Ghosh S, Ghosh G, Patra A. Implications of relaxation dynamics of collapsed conjugated polymeric nanoparticles for light-harvesting applications. Phys Chem Chem Phys 2021; 23:14549-14563. [DOI: 10.1039/d1cp01618k] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The mechanism of the formation of nanoparticles (collapsed state) from the extended state of polymers and their ultrafast excited state relaxation dynamics are illustrated.
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Affiliation(s)
- Arnab Ghosh
- School of Materials Sciences
- Indian Association for the Cultivation of Science
- Kolkata 700032
- India
| | - Srijon Ghosh
- School of Materials Sciences
- Indian Association for the Cultivation of Science
- Kolkata 700032
- India
| | - Goutam Ghosh
- School of Materials Sciences
- Indian Association for the Cultivation of Science
- Kolkata 700032
- India
| | - Amitava Patra
- School of Materials Sciences
- Indian Association for the Cultivation of Science
- Kolkata 700032
- India
- Institute of Nano Science and Technology
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14
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Di Maiolo F, Brey D, Binder R, Burghardt I. Quantum dynamical simulations of intra-chain exciton diffusion in an oligo (para-phenylene vinylene) chain at finite temperature. J Chem Phys 2020; 153:184107. [PMID: 33187420 DOI: 10.1063/5.0027588] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We report on quantum dynamical simulations of exciton diffusion in an oligo(para-phenylene vinylene) chain segment with 20 repeat units (OPV-20) at finite temperature, complementary to our recent study of the same system at T = 0 K [R. Binder and I. Burghardt, J. Chem. Phys. 152, 204120 (2020)]. Accurate quantum dynamical simulations are performed using the multi-layer multi-configuration time-dependent Hartree method as applied to a site-based Hamiltonian comprising 20 electronic states of Frenkel type and 460 vibrational modes, including site-local quinoid-distortion modes along with site-correlated bond-length alternation (BLA) modes, ring torsional modes, and an explicit harmonic-oscillator bath. A first-principles parameterized Frenkel-Holstein type Hamiltonian is employed, which accounts for correlations between the ring torsional modes and the anharmonically coupled BLA coordinates located at the same junction. Thermally induced fluctuations of the torsional modes are described by a stochastic mean-field approach, and their impact on the excitonic motion is characterized in terms of the exciton mean-squared displacement. A normal diffusion regime is observed under periodic boundary conditions, apart from transient localization features. Even though the polaronic exciton species are comparatively weakly bound, exciton diffusion is found to be a coherent-rather than hopping type-process, driven by the fluctuations of the soft torsional modes. Similar to the previous observations for oligothiophenes, the evolution for the most part exhibits a near-adiabatic dynamics of local exciton ground states (LEGSs) that adjust to the local conformational dynamics. However, a second mechanism, involving resonant transitions between neighboring LEGSs, gains importance at higher temperatures.
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Affiliation(s)
- Francesco Di Maiolo
- Institute for Physical and Theoretical Chemistry, Goethe University, Max-von-Laue-Str. 7, 60438 Frankfurt/Main, Germany
| | - Dominik Brey
- Institute for Physical and Theoretical Chemistry, Goethe University, Max-von-Laue-Str. 7, 60438 Frankfurt/Main, Germany
| | - Robert Binder
- Institute for Physical and Theoretical Chemistry, Goethe University, Max-von-Laue-Str. 7, 60438 Frankfurt/Main, Germany
| | - Irene Burghardt
- Institute for Physical and Theoretical Chemistry, Goethe University, Max-von-Laue-Str. 7, 60438 Frankfurt/Main, Germany
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15
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Hegger R, Binder R, Burghardt I. First-Principles Quantum and Quantum-Classical Simulations of Exciton Diffusion in Semiconducting Polymer Chains at Finite Temperature. J Chem Theory Comput 2020; 16:5441-5455. [PMID: 32786907 DOI: 10.1021/acs.jctc.0c00351] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
We report on first-principles quantum-dynamical and quantum-classical simulations of photoinduced exciton dynamics in oligothiophene chain segments, representative of intrachain exciton migration in the poly(3-hexylthiophene) (P3HT) polymer. Following up on our recent study (Binder R.; Burghardt, I. Faraday Discuss. 2020, 221, 406), multilayer multiconfiguration time-dependent Hartree calculations for a short oligothiophene segment comprising 20 monomer units (OT-20) are carried out to obtain full quantum-dynamical simulations at finite temperature. These are employed to benchmark mean-field Ehrenfest calculations, which are shown to give qualitatively correct results for the present system. Periodic boundary conditions turn out to significantly improve earlier estimates of diffusion coefficients. Using the Ehrenfest approach, a series of calculations are subsequently carried out for larger lattices (OT-40 to OT-80), leading to estimates for temperature-dependent mean-squared displacements, which are found to exhibit a near-linear dependence as a function of time. The resulting diffusion coefficient estimates are an increasing function of temperature, whose detailed functional form depends on the degree of static disorder. With a realistic static disorder parameter (σs ≃ 0.06 eV), the diffusion coefficients decrease from D ∼ 1 × 10-2 cm2 s-1 to D ∼ 1 × 10-3 cm2 s-1, in qualitative agreement with experimental data for P3HT. The dynamical scenario obtained from our simulations shows that exciton migration in P3HT-type chains is a largely adiabatic process throughout the temperature regime we investigated (i.e., T = 50-300 K). The resulting picture of exciton migration is a coherent, but not bandlike, motion of an exciton-polaron driven by fluctuations induced by low-frequency modes. This process acquires partial hopping character if static disorder becomes prominent and Anderson localization sets in.
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Affiliation(s)
- Rainer Hegger
- Institute for Physical and Theoretical Chemistry, Goethe University, Max-von-Laue-Strasse 7, 60438 Frankfurt/Main, Germany
| | - Robert Binder
- Institute for Physical and Theoretical Chemistry, Goethe University, Max-von-Laue-Strasse 7, 60438 Frankfurt/Main, Germany
| | - Irene Burghardt
- Institute for Physical and Theoretical Chemistry, Goethe University, Max-von-Laue-Strasse 7, 60438 Frankfurt/Main, Germany
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16
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Predicting optical spectra for optoelectronic polymers using coarse-grained models and recurrent neural networks. Proc Natl Acad Sci U S A 2020; 117:13945-13948. [PMID: 32513725 DOI: 10.1073/pnas.1918696117] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Coarse-grained modeling of conjugated polymers has become an increasingly popular route to investigate the physics of organic optoelectronic materials. While ultraviolet (UV)-vis spectroscopy remains one of the key experimental methods for the interrogation of these materials, a rigorous bridge between simulated coarse-grained structures and spectroscopy has not been established. Here, we address this challenge by developing a method that can predict spectra of conjugated polymers directly from coarse-grained representations while avoiding repetitive procedures such as ad hoc back-mapping from coarse-grained to atomistic representations followed by spectral computation using quantum chemistry. Our approach is based on a generative deep-learning model: the long-short-term memory recurrent neural network (LSTM-RNN). The latter is suggested by the apparent similarity between natural languages and the mathematical structure of perturbative expansions of, in our case, excited-state energies perturbed by conformational fluctuations. We also use this model to explore the level of sensitivity of spectra to the coarse-grained representation back-mapping protocol. Our approach presents a tool uniquely suited for improving postsimulation analysis protocols, as well as, potentially, for including spectral data as input in the refinement of coarse-grained potentials.
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17
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Patel K, Bittner ER. Mixed Quantum Classical Simulations of Charge-Transfer Dynamics in a Model Light-Harvesting Complex. I. Charge-Transfer Dynamics. J Phys Chem B 2020; 124:2149-2157. [PMID: 32118437 DOI: 10.1021/acs.jpcb.0c00202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We develop here a mixed quantum mechanical/molecular dynamics model to investigate charge-transfer dynamics in a set of large organic donor-bridge-acceptor triad molecules. Specifically, we are interested in the differences in electron and nuclear behavior relating to small changes in the molecular makeup of carotenoid-porphyrin-fullerene triads. Our model approximates excitation energies on the order of 1.9 eV which agree with absorption spectra for these triads and isolated porphyrins. Using electron population analysis, we monitor charge migration to the acceptor in time. Approximations of the charge transfer rates reveal ultrafast (picosecond scale) electron dynamics consistent with experimental literature.
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Affiliation(s)
- Kush Patel
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
| | - Eric R Bittner
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States.,Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom
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18
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Liao CK, Phan J, Martinez-Barron H, Mahmoud MA. Modulating the Optical Band Gap of Small Semiconducting Two-Dimensional Materials by Conjugated Polymers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:2574-2583. [PMID: 32090574 DOI: 10.1021/acs.langmuir.9b03335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Ultra-high-resolution optical microscopic techniques are used to measure the reflectance and photoluminescence (PL) spectrum of individual monolayered MoS2 of dimensions below 200 × 200 nm, while placed on top of a thin film conjugated polymer (CP). p-type and n-type CPs such as poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM), respectively, modified the optical band gap of the MoS2 sheet differently. However, the optical band gap is decreased after integration with P3HT, while it is increased after being combined with PCBM. The acceptable reason for the modification of the band gap of MoS2 by CPs is the generation of interlayer excitons (ILE) at their interface. The optical band gap of MoS2 is further changed by introducing an inert polymer spacer of different thickness to separate MoS2 from the CP. This is attributed to the reduction of the efficiency of excitonic interactions and lowering the exciton binding energy, which is induced by the increase of the dielectric function at the CP-MoS2 interface. No sign of electron injection to the conduction band of MoS2 after integration with P3HT or PCBM, as no significant shift of the A1' Raman band of MoS2 was measured on top of CPs, which is sensitive to the electron injection.
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Affiliation(s)
- Chih-Kai Liao
- Department of Biomedical Engineering and Chemical Engineering, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
| | - Jasmine Phan
- Department of Biomedical Engineering and Chemical Engineering, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
| | - Heber Martinez-Barron
- Department of Mechanical Engineering, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
| | - Mahmoud A Mahmoud
- Department of Biomedical Engineering and Chemical Engineering, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
- Department of Chemistry, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
- Department of Physics and Astronomy, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
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19
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Binder R, Burghardt I. First-principles quantum simulations of exciton diffusion on a minimal oligothiophene chain at finite temperature. Faraday Discuss 2020; 221:406-427. [PMID: 31596291 DOI: 10.1039/c9fd00066f] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
High-dimensional multiconfigurational quantum dynamics simulations are carried out at finite temperature to simulate exciton diffusion on an oligothiophene chain, representative of a segment of the poly(3-hexylthiophene) (P3HT) polymer. The ab initio parametrized site-based Hamiltonian of Binder et al. [Phys. Rev. Lett., 2018, 120, 227401] is employed to model a 20-site system, including intra-ring and inter-ring high-frequency modes as well as torsional modes which undergo thermal fluctuations induced by an explicit harmonic oscillator bath. The system-bath dynamics is treated within the setting of a stochastic mean-field Schrödinger equation. For the 20-site excitonic system, a total of 20 Frenkel states and 248 modes are propagated using the multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) method. The resulting dynamics can be interpreted in terms of the coherent motion of an exciton-polaron quasi-particle stochastically driven by torsional fluctuations. This dynamics yields a near-linear mean squared displacement (MSD) as a function of time, from which a diffusion coefficient can be deduced which increases with temperature, up to 5.7 × 10-3 cm2 s-1 at T = 300 K.
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Affiliation(s)
- Robert Binder
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt am Main, Germany.
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20
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Danielsen SPO, Davidson EC, Fredrickson GH, Segalman RA. Absence of Electrostatic Rigidity in Conjugated Polyelectrolytes with Pendant Charges. ACS Macro Lett 2019; 8:1147-1152. [PMID: 35619444 DOI: 10.1021/acsmacrolett.9b00551] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The delocalization of electrons in conjugated polymers impacts their chain shape, affecting their local ordering, self-assembly, and ultimately charge transport. Conjugated polyelectrolytes introduce electrostatic interactions as a molecular design parameter to potentially tune chain rigidity by combining the π-conjugated polymer backbone with pendant ionic groups. In conventional polyelectrolytes, the self-repulsion of the bound charges induce extended rod-like chain configurations. Here, we leverage small-angle neutron scattering to measure the chain shapes of model conjugated polymers in dilute solution with controlled fractions of randomly distributed pendant charges. We find these model polythiophenes are semiflexible, with a persistence length of approximately 3 nm, regardless of charge fraction, suggesting the effective absence of electrostatic rigidity in conjugated polyelectrolytes. While the overall persistence length is negligibly impacted by pendant charges, optical spectroscopy indicates that the pendant charges increase the backbone torsion between thiophene rings without significantly impacting the π-conjugation length (the length of electron delocalization along a nearly planar backbone) in dilute solution. These results indicate the effective decoupling of the pendant ionic charges from the overall chain conformation with implications for solution processing of organic semiconductors.
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Affiliation(s)
| | - Emily C. Davidson
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States
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21
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Lee EMY, Willard AP. Solving the Trivial Crossing Problem While Preserving the Nodal Symmetry of the Wave Function. J Chem Theory Comput 2019; 15:4332-4343. [PMID: 31305997 PMCID: PMC6750758 DOI: 10.1021/acs.jctc.9b00302] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
In
an adiabatic mixed quantum-classical simulation, the avoided
crossing of weakly coupled eigenstates can lead to unphysical discontinuities
in wave function dynamics, otherwise known as the trivial crossing
problem. A standard solution to the trivial crossing problem eliminates
spatial discontinuities in wave function dynamics by imposing changes
to the eigenstate of the wave function. In this paper, we show that
this solution has the side effect of introducing transient discontinuities
in the nodal symmetry of the wave function. We present an alternative
solution to the trivial crossing problem that preserves both the spatial
and nodal structure of the adiabatic wave function. By considering
a model of exciton dynamics on conjugated polymer systems, we show
that failure to preserve wave function symmetry yields exciton dynamics
that depends unphysically on polymer system size. We demonstrate that
our symmetry-preserving solution to the trivial crossing problem yields
more realistic dynamics and can thus improve the accuracy of simulations
of larger systems that are prone to the trivial crossing problem.
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Affiliation(s)
- Elizabeth M Y Lee
- Pritzker School of Molecular Engineering , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Adam P Willard
- Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
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22
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Lankevich V, Bittner ER. Relating free energy and open-circuit voltage to disorder in organic photovoltaic systems. J Chem Phys 2018; 149:244123. [DOI: 10.1063/1.5050506] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Affiliation(s)
- V. Lankevich
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
| | - E. R. Bittner
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
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23
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Raithel D, Simine L, Pickel S, Schötz K, Panzer F, Baderschneider S, Schiefer D, Lohwasser R, Köhler J, Thelakkat M, Sommer M, Köhler A, Rossky PJ, Hildner R. Direct observation of backbone planarization via side-chain alignment in single bulky-substituted polythiophenes. Proc Natl Acad Sci U S A 2018; 115:2699-2704. [PMID: 29483262 PMCID: PMC5856543 DOI: 10.1073/pnas.1719303115] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The backbone conformation of conjugated polymers affects, to a large extent, their optical and electronic properties. The usually flexible substituents provide solubility and influence the packing behavior of conjugated polymers in films or in bad solvents. However, the role of the side chains in determining and potentially controlling the backbone conformation, and thus the optical and electronic properties on the single polymer level, is currently under debate. Here, we investigate directly the impact of the side chains by studying the bulky-substituted poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT) and the common poly(3-hexylthiophene) (P3HT), both with a defined molecular weight and high regioregularity, using low-temperature single-chain photoluminescence (PL) spectroscopy and quantum-classical simulations. Surprisingly, the optical transition energy of PDOPT is significantly (∼2,000 cm-1 or 0.25 eV) red-shifted relative to P3HT despite a higher static and dynamic disorder in the former. We ascribe this red shift to a side-chain induced backbone planarization in PDOPT, supported by temperature-dependent ensemble PL spectroscopy. Our atomistic simulations reveal that the bulkier 2,5-dioctylphenyl side chains of PDOPT adopt a clear secondary helical structural motif and thus protect conjugation, i.e., enforce backbone planarity, whereas, for P3HT, this is not the case. These different degrees of planarity in both thiophenes do not result in different conjugation lengths, which we found to be similar. It is rather the stronger electronic coupling between the repeating units in the more planar PDOPT which gives rise to the observed spectral red shift as well as to a reduced calculated electron-hole polarization.
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Affiliation(s)
- Dominic Raithel
- Experimental Physics IV, University of Bayreuth, 95440 Bayreuth, Germany
| | - Lena Simine
- Department of Chemistry, Rice University, Houston, TX 77005
| | - Sebastian Pickel
- Experimental Physics IV, University of Bayreuth, 95440 Bayreuth, Germany
| | - Konstantin Schötz
- Experimental Physics II, University of Bayreuth, 95440 Bayreuth, Germany
| | - Fabian Panzer
- Experimental Physics II, University of Bayreuth, 95440 Bayreuth, Germany
| | | | - Daniel Schiefer
- Institute of Macromolecular Chemistry, University of Freiburg, 79104 Freiburg, Germany
| | - Ruth Lohwasser
- Applied Functional Polymers, University of Bayreuth, 95440 Bayreuth, Germany
| | - Jürgen Köhler
- Experimental Physics IV, University of Bayreuth, 95440 Bayreuth, Germany
- Bayreuth Institute of Macromolecular Research, University of Bayreuth, 95440 Bayreuth, Germany
| | - Mukundan Thelakkat
- Applied Functional Polymers, University of Bayreuth, 95440 Bayreuth, Germany
| | - Michael Sommer
- Institute of Macromolecular Chemistry, University of Freiburg, 79104 Freiburg, Germany
| | - Anna Köhler
- Experimental Physics II, University of Bayreuth, 95440 Bayreuth, Germany
- Bayreuth Institute of Macromolecular Research, University of Bayreuth, 95440 Bayreuth, Germany
| | - Peter J Rossky
- Department of Chemistry, Rice University, Houston, TX 77005
| | - Richard Hildner
- Experimental Physics IV, University of Bayreuth, 95440 Bayreuth, Germany;
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24
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Hu Z, Shao B, Geberth GT, Vanden Bout DA. Effects of molecular architecture on morphology and photophysics in conjugated polymers: from single molecules to bulk. Chem Sci 2018; 9:1101-1111. [PMID: 29675155 PMCID: PMC5887865 DOI: 10.1039/c7sc03465b] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 12/30/2017] [Indexed: 01/16/2023] Open
Abstract
A definitive comprehension of morphology and photophysics in conjugated polymers at multiple length scales demands both single molecule spectroscopy and well-controlled molecular architectures.
Conjugated polymers (CPs) possess a wide range of desirable properties, including accessible energetic bandgaps, synthetic versatility, and mechanical flexibility, which make them attractive for flexible and wearable optoelectronic devices. An accurate and comprehensive understanding about the morphology–photophysics relations in CPs lays the groundwork for their development in these applications. However, due to the complex roles of chemical structure, side-chains, backbone, and intramolecular interactions, CPs can exhibit heterogeneity in both their morphology and optoelectronic properties even at the single chain level. This molecular level heterogeneity together with complicated intermolecular interactions found in bulk CP materials severely obscures the deterministic information about the morphology and photophysics at different hierarchy levels. To counter this complexity and offer a clearer picture for the properties of CP materials, we highlight the approach of probing material systems with specific structural features via single molecule/aggregate spectroscopy (SMS). This review article covers recent advances achieved through such an approach regarding the important morphological and photophysical properties of CPs. After a brief review of the typical characteristics of CPs, we present detailed discussions of structurally well-defined model systems of CPs, from manipulated backbones and side-chains, up to nano-aggregates, studied with SMS to offer deterministic relations between morphology and photophysics from single chains building up to bulk states.
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Affiliation(s)
- Zhongjian Hu
- Department of Chemistry , University of Texas at Austin , USA .
| | - Beiyue Shao
- Department of Chemistry , University of Texas at Austin , USA .
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25
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Wang CI, Hsu CH, Hua CC. The correspondence between the conformational and chromophoric properties of amorphous conjugated polymers in mesoscale condensed systems. Phys Chem Chem Phys 2017; 19:20818-20828. [PMID: 28744545 DOI: 10.1039/c7cp03415f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
For π-conjugated polymers, the notion of spectroscopic units or "chromophores" provides illuminating insights into the experimentally observed absorption/emission spectra and the mechanisms of energy/charge transfer. To date, however, no statistical analysis has revealed a direct correspondence between chromophoric and conformational properties-with the latter being fundamental to polymer semiconductors. Herein, we propose a "persistence length" calculation to re-evaluate chain conformation over a full conjugation length. The mesoscale condensed systems of MEH-PPV and MEH-PPV/C60 hybrid (system size ∼10 × 10 × 10 nm3) are utilized as two prototypical model systems, along with a full range of segmental lengths (2-20-mer) and five lowest singlet excited states to hint at the generality of the features presented. We demonstrate, for the first time, that two properly re-defined conformational factors that characterize chain folding and planarity, respectively, capture excellently the population distribution of chromophores in both systems investigated. In contrast, the conventional strategy of utilizing two adjacent monomer units to characterize (local) chain conformation results in only an inconspicuous correlation between the two, as previously reported. It is further shown that chain folding-and not chain planarity-is more relevant in capturing the associated oscillator strength for the first excited state, where the transient dipole moments are known to align with the chain conformation, although the corresponding excitation energy and exciton size seem relatively unaffected. The observed effects of C60 on the MEH-PPV adsorption spectra also agree with recent experimental trends. Overall, the present findings are expected to aid future multiscale computer simulations and spectroscopy-data interpretations for polymer semiconductors and their hybrid systems.
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Affiliation(s)
- Chun I Wang
- Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 62102, Taiwan, Republic of China.
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