1
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Hu T, Han G, Guo Y, Yu K, Yi Y. Efficient and Accurate Estimation of Electronic Polarization Energies for Organic Semiconductors: An Embedding Charge Quantum Mechanics/Continuum Dielectric Model. J Chem Theory Comput 2024. [PMID: 38870475 DOI: 10.1021/acs.jctc.4c00244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2024]
Abstract
Electronic polarization plays a pivotal role in determining the molecular energy levels of organic semiconductors (OSCs) in the condensed phase. However, accurate estimation of the electronic polarization energy is a challenging task due to the intricate imbalance between the precision and efficiency. In this work, we have developed an embedding charge quantum mechanics/continuum dielectric (EC-QM/CD) model, which enables quantitative evaluation of the ionization potential (IP), electron affinity (EA), and polarization energy in both crystalline and amorphous solids for OSCs. The benchmark calculations on both p-type OSCs of oligoacenes and n-type OSCs of A-D-A small-molecule acceptors show that the values of IP, EA, and polarization energy obtained by EC-QM/CD are in good accordance with the experimental measurements or the results by high-precision methods, while the computational costs are substantially reduced. Given its balance between the accuracy and efficiency, the EC-QM/CD model exhibits considerable potential to broaden the applications in the field of OSCs, for instance, high-throughput screening by using solid-state energy levels or polarization energies as critical descriptors.
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Affiliation(s)
- Taiping Hu
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Guangchao Han
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Yuan Guo
- Faculty of Light Industry, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
| | - Kuang Yu
- Tsinghua-Berkeley Shenzhen Institute and Institute of Materials Research (iMR), Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
| | - Yuanping Yi
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
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2
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Berghuis AM, Tichauer RH, de Jong LMA, Sokolovskii I, Bai P, Ramezani M, Murai S, Groenhof G, Gómez Rivas J. Controlling Exciton Propagation in Organic Crystals through Strong Coupling to Plasmonic Nanoparticle Arrays. ACS PHOTONICS 2022; 9:2263-2272. [PMID: 35880071 PMCID: PMC9306002 DOI: 10.1021/acsphotonics.2c00007] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Exciton transport in most organic materials is based on an incoherent hopping process between neighboring molecules. This process is very slow, setting a limit to the performance of organic optoelectronic devices. In this Article, we overcome the incoherent exciton transport by strongly coupling localized singlet excitations in a tetracene crystal to confined light modes in an array of plasmonic nanoparticles. We image the transport of the resulting exciton-polaritons in Fourier space at various distances from the excitation to directly probe their propagation length as a function of the exciton to photon fraction. Exciton-polaritons with an exciton fraction of 50% show a propagation length of 4.4 μm, which is an increase by 2 orders of magnitude compared to the singlet exciton diffusion length. This remarkable increase has been qualitatively confirmed with both finite-difference time-domain simulations and atomistic multiscale molecular dynamics simulations. Furthermore, we observe that the propagation length is modified when the dipole moment of the exciton transition is either parallel or perpendicular to the cavity field, which opens a new avenue for controlling the anisotropy of the exciton flow in organic crystals. The enhanced exciton-polariton transport reported here may contribute to the development of organic devices with lower recombination losses and improved performance.
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Affiliation(s)
- Anton Matthijs Berghuis
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - Ruth H. Tichauer
- Nanoscience
Center and Department of Chemistry, University
of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland
| | - Lianne M. A. de Jong
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - Ilia Sokolovskii
- Nanoscience
Center and Department of Chemistry, University
of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland
| | - Ping Bai
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - Mohammad Ramezani
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - Shunsuke Murai
- Department
of Material Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, 6158510, Kyoto, Japan
| | - Gerrit Groenhof
- Nanoscience
Center and Department of Chemistry, University
of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland
| | - Jaime Gómez Rivas
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
- Institute
for Complex Molecular Systems ICMS, Eindhoven
University of Technology, P.O. Box 513, 5612 AJ, Eindhoven, The Netherlands
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3
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Xie X, Troisi A. Evaluating the Electronic Structure of Coexisting Excitonic and Multiexcitonic States in Periodic Systems: Significance for Singlet Fission. J Chem Theory Comput 2021; 18:394-405. [PMID: 34902251 DOI: 10.1021/acs.jctc.1c00831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Singlet fission (SF) in organic molecular solids is an example of a process that is challenging to describe with the most common electronic structure approaches. It involves optically bright singlet excited states delocalized over many molecules, which could be efficiently treated by density functional theory, and multiexcitonic localized states that have to be studied with wavefunction methods, usually with small clusters considering their expensive computational costs. In this work, we propose a methodology to combine multiconfigurational wavefunction calculations with reduced Hamiltonian to investigate the electronic structure of large clusters or fully periodic systems. The method is applied to the prototypical SF materials tetracene and pentacene. The results allow one to study how states of different natures (excitonic, charge-transfer, and multiexcitonic) coexist and are contaminated by their couplings in large or periodic systems. Novel insights are therefore possible. For example, because the excitonic bands are relatively broad with respect to the multiexcitonic states, there are limited regions of the crystal momentum space where the transition between the two is more likely.
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Affiliation(s)
- Xiaoyu Xie
- Department of Chemistry, University of Liverpool, Liverpool L69 3BX, U.K
| | - Alessandro Troisi
- Department of Chemistry, University of Liverpool, Liverpool L69 3BX, U.K
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4
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Koo S, Park I, Watanabe K, Taniguchi T, Shim JH, Ryu S. Extraordinary Photostability and Davydov Splitting in BN-Sandwiched Single-Layer Tetracene Molecular Crystals. NANO LETTERS 2021; 21:6600-6608. [PMID: 34283620 DOI: 10.1021/acs.nanolett.1c02009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Two-dimensional molecular crystals have been beyond the reach of systematic investigation because of the lack or instability of their well-defined forms. Here, we demonstrate drastically enhanced photostability and Davydov splitting in single and few-layer tetracene (Tc) crystals sandwiched between inorganic 2D crystals of graphene or hexagonal BN. Molecular orientation and long-range order mapped with polarized wide-field photoluminescence imaging and optical second-harmonic generation revealed high crystallinity of the 2D Tc and its distinctive orientational registry with the 2D inorganic crystals, which were also verified with first-principles calculations. The reduced dielectric screening in 2D space was manifested by enlarged Davydov splitting and attenuated vibronic sidebands in the excitonic absorption and emission of monolayer Tc crystals. Photostable 2D molecular crystals and their size effects will lead to novel photophysical principles and photonic applications.
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Affiliation(s)
- Seonghyun Koo
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 37673, Korea
| | - Ina Park
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 37673, Korea
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Ji Hoon Shim
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 37673, Korea
- Department of Physics and Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang (POSTECH), Pohang 37673, Republic of Korea
| | - Sunmin Ryu
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 37673, Korea
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5
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Nematiaram T, Padula D, Troisi A. Bright Frenkel Excitons in Molecular Crystals: A Survey. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2021; 33:3368-3378. [PMID: 34526736 PMCID: PMC8432684 DOI: 10.1021/acs.chemmater.1c00645] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 04/14/2021] [Indexed: 05/12/2023]
Abstract
We computed the optical properties of a large set of molecular crystals (∼2200 structures) composed of molecules whose lowest excited states are strongly coupled and generate wide excitonic bands. Such bands are classified in terms of their dimensionality (1-, 2-, and 3-dimensional), the position of the optically allowed state in relation with the excitonic density of states, and the presence of Davydov splitting. The survey confirms that one-dimensional aggregates are rare in molecular crystals highlighting the need to go beyond the simple low-dimensional models. Furthermore, this large set of data is used to search for technologically interesting and less common properties. For instance, we considered the largest excitonic bandwidth that is achievable within known molecular crystals and identified materials with strong super-radiant states. Finally, we explored the possibility that strong excitonic coupling can be used to generate emissive states in the near-infrared region in materials formed by molecules with bright visible absorption and we could identify the maximum allowable red shift in this material class. These insights with the associated searchable database provide practical guidelines for designing materials with interesting optical properties.
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Affiliation(s)
- Tahereh Nematiaram
- Department
of Chemistry and Materials Innovation Factory, University of Liverpool, Liverpool L69 7ZD, U.K.
| | - Daniele Padula
- Dipartimento
di Biotecnologie, Chimica e Farmacia, Università
di Siena, via A. Moro 2, Siena 53100, Italy
| | - Alessandro Troisi
- Department
of Chemistry and Materials Innovation Factory, University of Liverpool, Liverpool L69 7ZD, U.K.
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6
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Qian Y, Li X, Harutyunyan AR, Chen G, Rao Y, Chen H. Herzberg-Teller Effect on the Vibrationally Resolved Absorption Spectra of Single-Crystalline Pentacene at Finite Temperatures. J Phys Chem A 2020; 124:9156-9165. [PMID: 33103890 DOI: 10.1021/acs.jpca.0c07896] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The line shape of an electronic spectrum conveys the coupling between electronic and vibrational degrees of freedom. In the present study, the light absorption spectra of single-crystalline pentacene were measured by polarized UV-vis microscopy at 77, 185, and 293 K. The vibronic coupling encoded in each spectrum was resolved by the Herzberg-Teller theory that considers the contributions from the Franck-Condon (FC) factor, Franck-Condo/Herzberg-Teller (FC/HT) interference, and Herzberg-Teller (HT) coupling. Specifically, excitation energies, electronic transition dipole moments, and their nuclear gradients were evaluated by the GW method to ensure numerical accuracy, while the computationally efficient density function theory was employed to determine the optimized structures and vibrational normal modes. For every pair of electronic transition and normal mode that gives rise to a strong vibronic transition intensity, we examined their spatial characteristics by projecting them onto the three crystal axes. It was found that all normal modes strongly coupled to the lowest-lying a-polarized electronic transitions oscillate along axis a, whereas none of their counterparts for the lowest-lying b-polarized electronic transitions is predominantly along axis b. This notable difference on the alignment between the electronic transition and molecular vibration could help the directional control of charge dissociation and/or spin separation. Moreover, a significant variance of the destructive FC/HT interference was discovered with increasing temperatures that can well explain the a-polarized fading tableland near 650 nm. Finally, the importance of HT coupling was corroborated by comparing its intensity with those of FC factor and FC/HT interference. Taken all together, the vibrational dependence of the electronic wave function is critical to resolve the light absorption spectra of single-crystalline pentacene and its temperature effects, facilitating the systematic design of functional optical materials based on pentacene and its derivatives.
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Affiliation(s)
- Yuqin Qian
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Xia Li
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | | | - Gugang Chen
- Honda Research Institute USA, Inc., San Jose, California 95134, United States
| | - Yi Rao
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Hanning Chen
- Department of Chemistry, American University, Washington, D.C. 20016, United States
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7
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Van Schenck JDB, Mayonado G, Anthony JE, Graham MW, Ostroverkhova O. Molecular packing-dependent exciton dynamics in functionalized anthradithiophene derivatives: From solutions to crystals. J Chem Phys 2020; 153:164715. [PMID: 33138416 DOI: 10.1063/5.0026072] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Understanding the impact of inter-molecular orientation on the optical properties of organic semiconductors is important for designing next-generation organic (opto)electronic and photonic devices. However, fundamental aspects of how various features of molecular packing in crystalline systems determine the nature and dynamics of excitons have been a subject of debate. Toward this end, we present a systematic study of how various molecular crystal packing motifs affect the optical properties of a class of high-performance organic semiconductors: functionalized derivatives of fluorinated anthradithiophene. The absorptive and emissive species present in three such derivatives (exhibiting "brickwork," "twisted-columnar," and "sandwich-herringbone" motifs, controlled by the side group R) were analyzed both in solution and in single crystals, using various modalities of optical and photoluminescence spectroscopy, revealing the nature of these excited states. In solution, in the emission band, two states were identified: a Franck-Condon state present at all concentrations and an excimer that emerged at higher concentrations. In single crystal systems, together with ab initio calculations, it was found in the absorptive band that Frenkel and Charge Transfer (CT) excitons mixed due to nonvanishing CT integrals in all derivatives, but the amount of admixture and exciton delocalization depended on the packing, with the "sandwich-herringbone" packing motif least conducive to delocalization. Three emissive species in the crystal phase were also identified: Frenkel excitons, entangled triplet pairs 1(TT) (which are precursors to forming free triplet states via singlet fission), and self-trapped excitons (STEs, similar in origin to excimers present in concentrated solution). The "twisted-columnar" packing motif was most conducive to the formation of Frenkel excitons delocalized over 4-7 molecules depending on the temperature. These delocalized Frenkel states were dominant across the full temperature range (78 K-293 K), though at lower temperatures, the entangled triplet states and STEs were present. In the derivative with the "brickwork" packing, all three emissive species were observed across the full temperature range and, most notably, the 1(TT) state was present at room temperature. Finally, the derivative with the "sandwich-herringbone" packing exhibited localized Frenkel excitons and had a strong propensity for self-trapped exciton formation even at higher temperatures. In this derivative, no formation of the 1(TT) state was observed. The temperature-dependent dynamics of these emissive states are reported, as well as their origin in fundamental inter-molecular interactions.
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Affiliation(s)
- J D B Van Schenck
- Department of Physics, Oregon State University, Corvallis, Oregon 97330, USA
| | - G Mayonado
- Department of Physics, Oregon State University, Corvallis, Oregon 97330, USA
| | - J E Anthony
- Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, USA
| | - M W Graham
- Department of Physics, Oregon State University, Corvallis, Oregon 97330, USA
| | - O Ostroverkhova
- Department of Physics, Oregon State University, Corvallis, Oregon 97330, USA
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8
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Yoshida T, Watanabe K, Petrović M, Kralj M. Anomalous Temperature Dependence of Exciton Spectral Diffusion in Tetracene Thin Film. J Phys Chem Lett 2020; 11:5248-5254. [PMID: 32551650 DOI: 10.1021/acs.jpclett.0c01537] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In this work, an ultrafast spectral diffusion of the lowest exciton in a tetracene ultrathin film is studied by two-dimensional electronic spectroscopy. From the analysis of the nodal line slope, the frequency-fluctuation correlation function (FFCF) of the exciton band is extracted. The FFCF contains two components with decay times of 400 and 80 fs; while the former can be understood by a linear exciton-phonon coupling model, the latter shows an order of magnitude increase in its amplitude from 96 to 186 K that cannot be explained by the same model. A novel scheme of the energy-gap fluctuations is examined, in which an intramolecular high-frequency mode causes the spectral diffusion that is enhanced through an anharmonic coupling to low-frequency phonon modes. This finding provides a valuable input for future theoretical predictions on the ultrafast nonadiabatic dynamics of the molecular exciton.
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Affiliation(s)
- Tatsuya Yoshida
- Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Kazuya Watanabe
- Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Marin Petrović
- Center of Excellence for Advanced Materials and Sensing Devices, Institute of Physics, Bijenic̆ka 46, 10000 Zagreb, Croatia
| | - Marko Kralj
- Center of Excellence for Advanced Materials and Sensing Devices, Institute of Physics, Bijenic̆ka 46, 10000 Zagreb, Croatia
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9
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Ellis SR, Dietze DR, Rangel T, Brown-Altvater F, Neaton JB, Mathies RA. Resonance Raman Characterization of Tetracene Monomer and Nanocrystals: Excited State Lattice Distortions With Implications For Efficient Singlet Fission. J Phys Chem A 2019; 123:3863-3875. [PMID: 30952191 DOI: 10.1021/acs.jpca.9b02986] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The characterization of specific phonon modes and exciton states that lead to efficient singlet fission (SF) may be instrumental in the design of the next generation of high-efficiency photovoltaic devices. To this end, we analyze the absolute resonance Raman (RR) cross sections for tetracene (Tc) both as a monomer in solution and as a crystalline solid in an aqueous suspension of nanocrystals. For both systems, a time-dependent wavepacket model is developed that is consistent with the absolute RR cross sections, the magnitude of the absorption cross sections, and the vibronic line shapes of the fluorescence. In the monomer, the intramolecular reorganization energy is between 1500 and 1800 cm-1 and the solvent reorganization energy is 70 cm-1. In nanocrystals, the total reorganization is diminished to less than 600 cm-1. The lowest energy exciton has an estimated intramolecular reorganization energy between 300 and 500 cm-1 while intermolecular librational phonons have a reorganization energy of about 130 cm-1. The diminished reorganization energy of the nanocrystal is interpreted in the context of the delocalization of the band-edge exciton onto about ∼7 molecules. When electron and electron-hole correlations are included within many-body perturbation theory, the polarized absorption spectra of crystalline Tc are calculated and found to be in agreement with experiment. The low-lying exciton states and optically active phonons that contribute to the polarized crystal absorption are identified. The likely role of coherent exciton phonon evolution in the SF process is discussed.
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Affiliation(s)
- Scott R Ellis
- Department of Chemistry, MC 1460 , University of California at Berkeley , Berkeley , California 94720 , United States
| | - Daniel R Dietze
- Department of Chemistry, MC 1460 , University of California at Berkeley , Berkeley , California 94720 , United States
| | - Tonatiuh Rangel
- Department of Physics, MC 7300 , University of California at Berkeley , Berkeley , California 94720 , United States
| | - Florian Brown-Altvater
- Department of Physics, MC 7300 , University of California at Berkeley , Berkeley , California 94720 , United States
| | - Jeffrey B Neaton
- Department of Physics, MC 7300 , University of California at Berkeley , Berkeley , California 94720 , United States
| | - Richard A Mathies
- Department of Chemistry, MC 1460 , University of California at Berkeley , Berkeley , California 94720 , United States
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10
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Bayliss SL, Kraffert F, Wang R, Zhang C, Bittl R, Behrends J. Tuning Spin Dynamics in Crystalline Tetracene. J Phys Chem Lett 2019; 10:1908-1913. [PMID: 30939019 DOI: 10.1021/acs.jpclett.9b00356] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Tetracene is an archetypal material undergoing singlet fission-the generation of a pair of triplet excitons from one singlet exciton. Here, using time-resolved electron spin resonance, we show how the spin dynamics in tetracene crystals are influenced by temperature and morphology. Upon cooling from 300 to 200 K, we observe a switch between singlet fission and intersystem crossing generated triplets, manifesting as an inversion in transient spin polarization. We extract a spin dephasing time of approximately 40 ns for fission-generated triplets at room temperature, nearly 100 times shorter than the dephasing time that we measure for triplets localized on isolated tetracene molecules. These results highlight the importance of morphology and thermal activation in singlet fission systems.
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Affiliation(s)
- Sam L Bayliss
- Berlin Joint EPR Lab, Fachbereich Physik , Freie Universität Berlin , D-14195 Berlin , Germany
| | - Felix Kraffert
- Berlin Joint EPR Lab, Fachbereich Physik , Freie Universität Berlin , D-14195 Berlin , Germany
| | - Rui Wang
- National Laboratory of Solid State Microstructures, School of Physics , Nanjing University , Nanjing 210093 , China
| | - Chunfeng Zhang
- National Laboratory of Solid State Microstructures, School of Physics , Nanjing University , Nanjing 210093 , China
- Synergetic Innovation Center in Quantum Information and Quantum Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
| | - Robert Bittl
- Berlin Joint EPR Lab, Fachbereich Physik , Freie Universität Berlin , D-14195 Berlin , Germany
| | - Jan Behrends
- Berlin Joint EPR Lab, Fachbereich Physik , Freie Universität Berlin , D-14195 Berlin , Germany
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11
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Camposeo A, Granger DB, Parkin SR, Altamura D, Giannini C, Anthony JE, Pisignano D. Directed Functionalization Tailors the Polarized Emission and Waveguiding Properties of Anthracene-Based Molecular Crystals. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2019; 31:1775-1783. [PMID: 30918420 PMCID: PMC6429991 DOI: 10.1021/acs.chemmater.8b05361] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2018] [Revised: 02/03/2019] [Indexed: 06/09/2023]
Abstract
Organic semiconducting crystals are characterized by anisotropic optical and electronic properties, which can be tailored by controlling the packing of the constituent molecules in the crystal unit cell. Here, the synthesis, structural characterization, and emission of anthracene derivatives are focused to correlate directed functionalization and optical properties. These compounds are easily and scalably prepared by standard synthesis techniques, and alterations in functional groups yield materials with either exclusive edge-to-face or face-to-face solid-state interactions. The resulting crystals feature either platelet or needle shapes, and the emission exhibits polarization ratios up to 5 at room temperature. In needle-shaped crystals, self-waveguiding of the emission is also observed with propagation loss coefficients as low as 1.3 dB mm-1. Moreover, optical coupling between crossing crystalline microwires is found and characterized. The combination of optical anisotropy and emission self-waveguiding opens interesting routes for the exploitation of these active materials in photonic applications, including optical integrated circuits and microscale light sources.
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Affiliation(s)
- Andrea Camposeo
- NEST,
Istituto Nanoscienze-CNR, Piazza San Silvestro 12, I-56127 Pisa, Italy
| | - Devin B. Granger
- Center
for Applied Energy Research, University
of Kentucky, 2582 Research Park Drive, Lexington, Kentucky 40506, United States
| | - Sean R. Parkin
- Center
for Applied Energy Research, University
of Kentucky, 2582 Research Park Drive, Lexington, Kentucky 40506, United States
| | - Davide Altamura
- Istituto
di Cristallografia (IC-CNR), via Amendola 122/O, I-70126 Bari, Italy
| | - Cinzia Giannini
- Istituto
di Cristallografia (IC-CNR), via Amendola 122/O, I-70126 Bari, Italy
| | - John E. Anthony
- Center
for Applied Energy Research, University
of Kentucky, 2582 Research Park Drive, Lexington, Kentucky 40506, United States
| | - Dario Pisignano
- NEST,
Istituto Nanoscienze-CNR, Piazza San Silvestro 12, I-56127 Pisa, Italy
- Dipartimento
di Fisica, Università di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
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12
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Hestand NJ, Spano FC. Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer. Chem Rev 2018; 118:7069-7163. [PMID: 29664617 DOI: 10.1021/acs.chemrev.7b00581] [Citation(s) in RCA: 697] [Impact Index Per Article: 116.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The electronic excited states of molecular aggregates and their photophysical signatures have long fascinated spectroscopists and theoreticians alike since the advent of Frenkel exciton theory almost 90 years ago. The influence of molecular packing on basic optical probes like absorption and photoluminescence was originally worked out by Kasha for aggregates dominated by Coulombic intermolecular interactions, eventually leading to the classification of J- and H-aggregates. This review outlines advances made in understanding the relationship between aggregate structure and photophysics when vibronic coupling and intermolecular charge transfer are incorporated. An assortment of packing geometries is considered from the humble molecular dimer to more exotic structures including linear and bent aggregates, two-dimensional herringbone and "HJ" aggregates, and chiral aggregates. The interplay between long-range Coulomb coupling and short-range charge-transfer-mediated coupling strongly depends on the aggregate architecture leading to a wide array of photophysical behaviors.
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Affiliation(s)
- Nicholas J Hestand
- Department of Chemistry , Temple University , Philadelphia , Pennsylvania 19122 , United States
| | - Frank C Spano
- Department of Chemistry , Temple University , Philadelphia , Pennsylvania 19122 , United States
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13
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Zhu T, Wan Y, Huang L. Direct Imaging of Frenkel Exciton Transport by Ultrafast Microscopy. Acc Chem Res 2017; 50:1725-1733. [PMID: 28678469 DOI: 10.1021/acs.accounts.7b00155] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Long-range transport of Frenkel excitons is crucial for achieving efficient molecular-based solar energy harvesting. Understanding of exciton transport mechanisms is important for designing materials for solar energy applications. One major bottleneck in unraveling of exciton transport mechanisms is the lack of direct measurements to provide information in both spatial and temporal domains, imposed by the combination of fast energy transfer (typically ≤1 ps) and short exciton diffusion lengths (typically ≤100 nm). This challenge requires developing experimental tools to directly characterize excitation energy transport, and thus facilitate the elucidation of mechanisms. To address this challenge, we have employed ultrafast transient absorption microscopy (TAM) as a means to directly image exciton transport with ∼200 fs time resolution and ∼50 nm spatial precision. By mapping population in spatial and temporal domains, such approach has unraveled otherwise obscured information and provided important parameters for testing exciton transport models. In this Account, we discuss the recent progress in imaging Frenkel exciton migration in molecular crystals and aggregates by ultrafast microscopy. First, we establish the validity of the TAM methods by imaging singlet and triplet exciton transport in a series of polyacene single crystals that undergo singlet fission. A new singlet-mediated triplet transport pathway has been revealed by TAM, resulting from the equilibrium between triplet and singlet exciton populations. Such enhancement of triplet exciton transport enables triplet excitons to migrate as singlet excitons and leads to orders of magnitude faster apparent triplet exciton diffusion rate in the picosecond and nanosecond time scales, favorable for solar cell applications. Next we discuss how information obtained by ultrafast microscopy can evaluate coherent effects in exciton transport. We use tubular molecular aggregates that could support large exciton delocalization sizes as a model system. The initial experiments measure exciton diffusion constants of 3-6 cm2 s-1, 3-5 times higher than the incoherent limit predicted by theory, suggesting that coherent effects play a role. In summary, combining ultrafast spectroscopic methods with microscopic techniques provides a direct approach for obtaining important parameters to unravel the underlying exciton transport mechanisms in molecular solids. We discuss future directions to bridge the gap in understanding of fundamental energy transfer theories to include coherent and incoherent effects. We are still in the infancy of ultrafast microscopy, and the vast potential is not limited to the systems discussed in this Account.
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Affiliation(s)
- Tong Zhu
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Yan Wan
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Libai Huang
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
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14
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Pithan L, Beyer P, Bogula L, Zykov A, Schäfer P, Rawle J, Nicklin C, Opitz A, Kowarik S. Direct Photoalignment and Optical Patterning of Molecular Thin Films. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29:1604382. [PMID: 27906475 DOI: 10.1002/adma.201604382] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 10/02/2016] [Indexed: 06/06/2023]
Abstract
A novel strategy for direct photoalignment of molecular materials using optothermal re-orientation is introduced. Photoalignment for molecular materials such as the organic semiconductor tetracene is shown, without relying on additional photoreactive dopants or alignment layers. Patterning and polarized light emission, e.g., for polarized organic light emitting diodes is demonstrated.
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Affiliation(s)
- Linus Pithan
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
| | - Paul Beyer
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
| | - Laura Bogula
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
| | - Anton Zykov
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
| | - Peter Schäfer
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
| | - Jonathan Rawle
- Diamond Light Source Ltd, Harwell Science & Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK
| | - Chris Nicklin
- Diamond Light Source Ltd, Harwell Science & Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK
| | - Andreas Opitz
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
| | - Stefan Kowarik
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
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15
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Xu T, Wang W, Yin S, Wang Y. Evaluation of electronic polarization energy in oligoacene molecular crystals using the solvated supermolecular approach. Phys Chem Chem Phys 2017; 19:14453-14461. [DOI: 10.1039/c7cp01534h] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The solvated supermolecular approach, i.e., block-localized wave function coupled with polarizable continuum model (BLW/PCM), was proposed to calculate molecular ionization potential (IP), electron affinity (EA) in the solid phase, and related electronic polarization.
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Affiliation(s)
- Tao Xu
- Key Laboratory for Macromolecular Science of Shaanxi Province
- School of Chemistry and Chemical Engineering
- Shaanxi Normal University
- Xi'an city
- China
| | - Wenliang Wang
- Key Laboratory for Macromolecular Science of Shaanxi Province
- School of Chemistry and Chemical Engineering
- Shaanxi Normal University
- Xi'an city
- China
| | - Shiwei Yin
- Key Laboratory for Macromolecular Science of Shaanxi Province
- School of Chemistry and Chemical Engineering
- Shaanxi Normal University
- Xi'an city
- China
| | - Yun Wang
- Centre for Clean Environment and Energy
- Griffith School of Environment
- Griffith University
- Australia
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16
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Wan Y, Guo Z, Zhu T, Yan S, Johnson J, Huang L. Cooperative singlet and triplet exciton transport in tetracene crystals visualized by ultrafast microscopy. Nat Chem 2015; 7:785-92. [DOI: 10.1038/nchem.2348] [Citation(s) in RCA: 163] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Accepted: 09/14/2015] [Indexed: 12/22/2022]
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17
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Cudazzo P, Sottile F, Rubio A, Gatti M. Exciton dispersion in molecular solids. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:113204. [PMID: 25738755 DOI: 10.1088/0953-8984/27/11/113204] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The investigation of the exciton dispersion (i.e. the exciton energy dependence as a function of the momentum carried by the electron-hole pair) is a powerful approach to identify the exciton character, ranging from the strongly localised Frenkel to the delocalised Wannier-Mott limiting cases. We illustrate this possibility at the example of four prototypical molecular solids (picene, pentacene, tetracene and coronene) on the basis of the parameter-free solution of the many-body Bethe-Salpeter equation. We discuss the mixing between Frenkel and charge-transfer excitons and the origin of their Davydov splitting in the framework of many-body perturbation theory and establish a link with model approaches based on molecular states. Finally, we show how the interplay between the electronic band dispersion and the exchange electron-hole interaction plays a fundamental role in setting the nature of the exciton. This analysis has a general validity holding also for other systems in which the electron wavefunctions are strongly localized, as in strongly correlated insulators.
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Affiliation(s)
- Pierluigi Cudazzo
- Nano-Bio Spectroscopy group, Universidad del País Vasco, CFM CSIC-UPV/EHU-MPC and DIPC, E-20018 San Sebastián, Spain. European Theoretical Spectroscopy Facility (ETSF
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18
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Zhang B, Zhang C, Xu Y, Wang R, He B, Liu Y, Zhang S, Wang X, Xiao M. Polarization-dependent exciton dynamics in tetracene single crystals. J Chem Phys 2014; 141:244303. [DOI: 10.1063/1.4904385] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Affiliation(s)
- Bo Zhang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Chunfeng Zhang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yanqing Xu
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Rui Wang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Bin He
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yunlong Liu
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Shimeng Zhang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Xiaoyong Wang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Min Xiao
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
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19
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Birech Z, Schwoerer M, Schmeiler T, Pflaum J, Schwoerer H. Ultrafast dynamics of excitons in tetracene single crystals. J Chem Phys 2014; 140:114501. [PMID: 24655187 DOI: 10.1063/1.4867696] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states S(n) on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S1 on a 40 ps timescale. The high energy Davydov component of the S1 exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale.
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Affiliation(s)
- Zephania Birech
- Laser Research Institute, Stellenbosch University, Stellenbosch 7600, South Africa
| | - Markus Schwoerer
- Department of Physics, University of Bayreuth, Bayreuth, Germany
| | - Teresa Schmeiler
- Experimental Physics VI, University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg, Germany
| | - Jens Pflaum
- Experimental Physics VI, University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg, Germany
| | - Heinrich Schwoerer
- Laser Research Institute, Stellenbosch University, Stellenbosch 7600, South Africa
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20
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Chernikov A, Yaffe O, Kumar B, Zhong Y, Nuckolls C, Heinz TF. Spectroscopic Study of Anisotropic Excitons in Single Crystal Hexacene. J Phys Chem Lett 2014; 5:3632-3635. [PMID: 26278730 DOI: 10.1021/jz501693g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The linear optical response of hexacene single crystals over a spectral range of 1.3-1.9 eV was studied using polarization-resolved reflectance spectroscopy at cryogenic temperatures. We observe strong polarization anisotropy for all optical transitions. Pronounced deviations from the single-molecule, solution-phase spectra are present, with a measured Davydov splitting of 180 meV, indicating strong intermolecular coupling. The energies and oscillator strengths of the relevant optical transitions and polarization-dependent absorption coefficients are extracted from quantitative analysis of the data.
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Affiliation(s)
- Alexey Chernikov
- †Departments of Physics and Electrical Engineering, Columbia University, New York, New York 10027, United States
| | - Omer Yaffe
- †Departments of Physics and Electrical Engineering, Columbia University, New York, New York 10027, United States
| | - Bharat Kumar
- ‡Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Yu Zhong
- ‡Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Colin Nuckolls
- ‡Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Tony F Heinz
- †Departments of Physics and Electrical Engineering, Columbia University, New York, New York 10027, United States
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21
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D’Avino G, Muccioli L, Zannoni C, Beljonne D, Soos ZG. Electronic Polarization in Organic Crystals: A Comparative Study of Induced Dipoles and Intramolecular Charge Redistribution Schemes. J Chem Theory Comput 2014; 10:4959-71. [DOI: 10.1021/ct500618w] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Gabriele D’Avino
- Department
of Industrial Chemistry “Toso Montanari” and INSTM, University of Bologna, Viale del Risorgimento 4, IT-40136 Bologna, Bologna, Italy
| | - Luca Muccioli
- Department
of Industrial Chemistry “Toso Montanari” and INSTM, University of Bologna, Viale del Risorgimento 4, IT-40136 Bologna, Bologna, Italy
| | - Claudio Zannoni
- Department
of Industrial Chemistry “Toso Montanari” and INSTM, University of Bologna, Viale del Risorgimento 4, IT-40136 Bologna, Bologna, Italy
| | - David Beljonne
- Laboratory
for Chemistry of Novel Materials, University of Mons, Place du Parc
20, BE-7000 Mons, and
| | - Zoltán G. Soos
- Department
of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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22
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Visualization of exciton transport in ordered and disordered molecular solids. Nat Commun 2014; 5:3646. [DOI: 10.1038/ncomms4646] [Citation(s) in RCA: 220] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Accepted: 03/13/2014] [Indexed: 12/25/2022] Open
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23
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Wang X, Broch K, Scholz R, Schreiber F, Meixner AJ, Zhang D. Topography-Correlated Confocal Raman Microscopy with Cylindrical Vector Beams for Probing Nanoscale Structural Order. J Phys Chem Lett 2014; 5:1048-1054. [PMID: 26274447 DOI: 10.1021/jz500061y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Cylindrical vector beams, such as radially or azimuthally polarized doughnut beams, are combined with topography studies of pentacene thin films, allowing us to correlate Raman spectroscopy with intermolecular interactions depending on the particular pentacene polymorph. Polarization-dependent Raman spectra of the C-H bending vibrations are resolved layer by layer within a thin film of ∼20 nm thickness. The variation of the Raman peak positions indicates changes in the molecular orientation and in the local environment at different heights of the pentacene film. With the assistance of a theoretical model based on harmonic oscillator and perturbation theory, our method reveals the local structural order and the polymorph at different locations within the same pentacene thin film, depending mainly on its thickness. In good agreement with the crystallographic structures reported in the literature, our observations demonstrate that the first few monolayers grown in a structure are closer to the thin-film phase, but for larger film thicknesses, the morphology evolves toward the crystal-bulk phase with a larger tilting angle of the pentacene molecules against the substrate normal.
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Affiliation(s)
- Xiao Wang
- †Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Katharina Broch
- ‡Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Reinhard Scholz
- §Institut für Angewandte Photophysik, Technische Universität Dresden, D-01062 Dresden, Germany
| | - Frank Schreiber
- ‡Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Alfred J Meixner
- †Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Dai Zhang
- †Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
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24
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Persano L, Camposeo A, Pisignano D, Burini A, Spearman P, Tavazzi S. Electron-beam nanopatterning and spectral modulation of organic molecular light-emitting single crystals. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:1643-1649. [PMID: 24490972 DOI: 10.1021/la4033833] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The nanopatterning of light-emitting molecular crystals with semiconducting properties can be crucial for the development of future optoelectronic and nanoelectronic devices based on organic materials. In this respect, electron-beam writing is a powerful tool to realize patterns at the nanoscale, but it is still rarely applied to active organic materials. Here, sub-100-nm-scale nanopatterning is performed on the surface of quaterthiophene monocrystals by direct maskless electron-beam writing. Gratings are produced on organic crystals with periods ranging from 80 nm to 1 μm and single-line lateral dimensions ranging from 20 to 500 nm, with electron-beam exposure doses between 100 and 1500 μC/cm(2). The morphological and texturing properties of the pattern are discussed, together with the interaction mechanisms between the electron beam and the crystal. The resulting modulation of the light emission is consistent with Bragg scattering from the patterned periodic features.
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Affiliation(s)
- Luana Persano
- National Nanotechnology Laboratory (NNL), Istituto Nanoscienze-CNR , via Arnesano, I-73100 Lecce, Italy
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25
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Catalán J. On dimers and complexes of tetracene and the Kasha's molecular excitonic model. J PHYS ORG CHEM 2014. [DOI: 10.1002/poc.3283] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Javier Catalán
- Departamento de Quimica Fisica Aplicada; Universidad Autónoma de Madrid; 28049 Madrid Spain
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26
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Yamagata H, Norton J, Hontz E, Olivier Y, Beljonne D, Brédas JL, Silbey RJ, Spano FC. The nature of singlet excitons in oligoacene molecular crystals. J Chem Phys 2011; 134:204703. [DOI: 10.1063/1.3590871] [Citation(s) in RCA: 212] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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27
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Tavazzi S, Mora S, Alessandrini L, Silvestri L. Anisotropic optical functions of α-1,4,4-tetraphenyl-1,3-butadiene. J Chem Phys 2011; 134:034707. [PMID: 21261384 DOI: 10.1063/1.3524207] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
One of the known monoclinic polymorphs of 1,1,4,4-tetraphenyl-1,3-butadiene was grown by the floating-drop technique. This material is of interest for blue emitting devices and for fundamental studies on intermolecular interactions, excited states and vibronic coupling in the fields of chemical physics and materials science. Polarized UV-visible spectra are reported. The origin of the optical bands is resolved. The results give information on the intermolecular interactions and are compared with theoretical predictions and modeling. The full material dielectric tensor is provided, as deduced from generalized spectroscopic ellipsometry. Details on the use of this technique on strongly anisotropic and absorbing molecular materials are given. Some typical features of the optical spectra are also demonstrated to be very sensitive to the presence of misaligned domains, which, in our samples, are found to be rotated around the normal to the surface and whose amount is determined. The method allows discriminating among monocrystals, in-plane polycrystalline samples, layered samples formed by misaligned successive layers, or samples with both types of disorder. Two independent parameters giving the fraction of misaligned domains or layers are suggested for the characterization and optimization of the growth and deposition of molecular organic materials.
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Affiliation(s)
- Silvia Tavazzi
- Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, Via Cozzi 53, I-20125, Milano, Italy. silvia
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28
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Dressel M, Gompf B, Faltermeier D, Tripathi AK, Pflaum J, Schubert M. Kramers-Kronig-consistent optical functions of anisotropic crystals: generalized spectroscopic ellipsometry on pentacene. OPTICS EXPRESS 2008; 16:19770-8. [PMID: 19030062 DOI: 10.1364/oe.16.019770] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
The Kramers-Kronig relations between the real and imaginary parts of a response function are widely used in solid-state physics to evaluate the corresponding quantity if only one component is measured. They are among the most fundamental statements since only based on the analytical behavior and causal nature of the material response [Phys. Rev. 104, 1760-1770 (1956)]. Optical losses, for instance, can be obtained from the dispersion of the dielectric constant at all wavelengths, and vice versa [Handbook of optical constants of solids, Vol. 1, p. 35]. Although the general validity was never casted into doubt, it is a longstanding problem that Kramers-Kronig relations cannot simply be applied to anisotropic crystalline materials because contributions from different directions mix in a frequency-dependent way. Here we present a general method to identify frequency-independent principal polarizability directions for which the Kramers-Kronig relations are obeyed even in materials with lowest symmetry. Using generalized spectroscopic ellipsometry on a single crystal surface of triclinic pentacene, as an example, enables us to evaluate the complex dielectric constant and to compare it with band-structure calculations along the crystallographic directions. A general recipe is provided how to proceed from a macroscopic measurement on a low symmetry crystal plane to the microscopic dielectric properties of the unit cell, along whose axes the Kramers-Kronig relations hold.
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Affiliation(s)
- M Dressel
- Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany.
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