Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A11: Organic Electronics - Excited States and Energy TransferFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY DMP Chair: Bryan Boudouris, Purdue University Room: 270 |
Monday, March 13, 2017 8:00AM - 8:12AM |
A11.00001: Singlet-to-triplet intermediates and triplet exciton dynamics in pentacene thinfilms Verner Thorsmolle, Michael Korber, Emanuel Obergfell, Thomas Kuhlman, Ian Campbell, Brian Crone, Antoinette Taylor, Richard Averitt, Jure Demsar Singlet-to-triplet fission in organic semiconductors is a spin-conserving multiexciton process in which one spin-zero singlet excitation is converted into two spin-one triplet excitations on an ultrafast timescale. Current scientific interest into this carrier multiplication process is largely driven by prospects of enhancing the efficiency in photovoltaic applications by generating two long-lived triplet excitons by one photon. The fission process is known to involve intermediate states, known as correlated triplet pairs, with an overall singlet character, before being interchanged into uncorrelated triplets. Here we use broadband femtosecond real-time spectroscopy to study the excited state dynamics in pentacene thin films, elucidating the fission process and the role of intermediate triplet states. [Preview Abstract] |
Monday, March 13, 2017 8:12AM - 8:24AM |
A11.00002: Exciton transfer in self-assembled conjugated polyelectrolyte complexes~ Alexander Ayzner, William Hollingsworth, Carmen Segura, Jonathan Balderrama, Nathaniel Lopez, Pamela Schleissner Conjugated polyelectrolytes (CPEs) combine the remarkable properties of conjugated polymers and polyions, leading to the strong coupling between electronic structure and the solution ionosphere. With the aim of creating soft, artificial light-harvesting antennae, we have~for the first time~formed ionically assembled CPE complexes capable of electronic energy transfer in both aqueous solution and the solid state. We find that complex formation is an activated process, which leads to emergent excitonic states on the energy acceptor CPE. These states are characterized by substantial wavefunction delocalization along the polymer backbone, leading to an enhancement in the fluorescence quantum yield by roughly two orders of magnitude, as well as the possibility of coherent transfer. We also show that the chemical nature of excess ions and the solution ionic strength can have a drastic effect on cooperative complex assembly and the corresponding energy transfer dynamics. This indicates a possible path towards sensitive control of the light-harvesting efficiency using the electrostatic environment surrounding the CPE complex. [Preview Abstract] |
Monday, March 13, 2017 8:24AM - 8:36AM |
A11.00003: Frenkel-Charge-Transfer exciton intermixing theory for molecular crystals with two isolated Frenkel exciton states. Igor Bondarev, Adrian Popescu We develop an analytical theory for the intra-intermolecular exciton intermixing in periodic 1D chains of planar organic molecules with two isolated low-lying Frenkel exciton states, typical of copper phthalocyanine (CuPc) and other transition metal phthalocyanine molecules[1,2]. We formulate the Hamiltonian and use the exact Bogoliubov diagonalization procedure to derive the eigen energy spectrum for the two lowest intramolecular Frenkel excitons coupled to the intermolecular charge transfer (CT) exciton state. By comparing our theoretical spectrum with available experimental CuPc absorption data, we obtain the parameters of the Frenkel-CT exciton intermixing in CuPc thin films. The two Frenkel exciton states here are spaced apart by 0.26 eV, and the charge transfer exciton state is 50 meV above the lowest Frenkel exciton. Both Frenkel excitons are strongly mixed with the CT exciton, showing the coupling constant 0.17 eV in agreement with earlier electron transport experiments[3]. Our results can be used for the proper interpretation of the physical properties of crystalline phthalocyanines. -- [1]J.H.Sharp, M.Abkowitz, J. Phys. Chem. 77, 477 (1973); [2]L.Edwards, M.Gouterman, J. Mol. Spectr. 33, 292 (1970); [3]I.G.Hill at al., Chem. Phys. Lett. 327, 181 (2000). [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 8:48AM |
A11.00004: How far could energy transport within a single crystal. Yifan Zhang, Yanke Che, Jincai Zhao, Granick Steve Efficient transport of excitation energy over long distance is a vital process in light-harvesting systems and molecular electronics. The energy transfer distance is largely restricted by the probability decay of the exciton when hopping within a single crystal. Here, we fabricated an organic single crystal within which the energy could transfer more than 100 $\mu $m, a distance only limited by its crystal size. Our system could be regarded as a ``Sprint relay game'' performing on different surface of tracks. Photoinduced ``athletes'' (excitons) triggered intermolecular ``domino'' reaction to propagate energy for a long distance. In addition, athletes with the same ability runs much farther on smooth ideal track (single crystal assembled from merely van der Waals interaction) than bumpy mud track (crystal assembled from combination of pi-stacking, hydrogen bond and van der Waals interactions). Our finding presents new physics on enhancing energy transfer length within a single crystal. [Preview Abstract] |
Monday, March 13, 2017 8:48AM - 9:00AM |
A11.00005: Theory of excited state absorptions in pentacene crystals and films Sumitendra Mazumdar, Souratosh Khan There exists a disconnect between the experimental technique to detect singlet fission in organic molecular systems and current theoretical approaches to this process. Experimentally, singlet fission is detected by time-resolved ultrafast spectroscopy; existing theoretical approaches until now have not allowed calculations of excited state absorptions, and comparisons between experiment and theory are indirect. In this work we present a complete theory of ultrafast excited state absorptions in pentacene herringbone crystals and films. We first calculate ground state absorptions within the Parier-Parr-Pople Hamiltonian and show that our calculations give very good fit to the wavelength dependent absorption spectrum. We then calculate singlet and triplet photoinduced absorptions, and find that, (a) photoinduced molecular rotations leading to creation of nearest neighbor dimers is an essential first step to singlet fission, (b) dimer formation leads to both an excimer and a triplet-triplet state, and (c) while the earliest excited state absorption from the product triplets of singlet fission are intramolecular excitations, later triplet photoinduced absorptions are to an intermolecular charge-transfer state. [Preview Abstract] |
Monday, March 13, 2017 9:00AM - 9:12AM |
A11.00006: Modeling chain configurations of conjugated polymers as a function of charge concentration Brandon Wood, Yongwoo Shin, Kristin Persson Conjugated polymers are promising materials for energy storage and energy conversion applications due to their electronic and optical properties. The electronic structure of conjugated polymers plays an important role in determining individual chain configurations due to electron-phonon coupling interactions. In this work, we evaluated chain properties and configurations as a function of charge concentration using a simplified model based on first-principles calculations that captures the electronic structure changes. Our computations~indicate~that the charge concentration modifies the backbone stiffness in polythiophenes, which is manifested by changes in classical properties such as persistence length and end-to-end distance. [Preview Abstract] |
Monday, March 13, 2017 9:12AM - 9:48AM |
A11.00007: Spin-pumping into organic semiconductors with tunable spin-orbit coupling Invited Speaker: Zeev Valy Vardeny Spin-current that is generated in organic semiconductors via the process of `spin-pumping' from ferromagnetic (FM) substrates subjected to resonant microwave absorption has attracted recently great interest, since this scheme circumvents the impedance mismatch between the organic semiconductor (OSEC) and FM injector that exists in the `spin injection' technique. Because of the weak spin-orbit coupling (SOC) in most OSECs, the resulting inverse spin Hall effect (ISHE) in these materials is expected to be subtle, and thus limited by the microwave power applicable under continuous-wave (cw) excitation. In this talk we will describe the ISHE technique using pulsed ferromagnetic resonance, where the ISHE current is \textasciitilde 2-3 orders of magnitude larger compared to that generated using cw excitation. This approach enables us to investigate the ISHE in a variety of OSECs and organic-inorganic perovskites having tunable SOC ranging from strong SOC (Pt-rich polymers and perovskites), to weak SOC polymers (such as DOO-PPV, PEDOT:PSS), to C$_{60}$ films, where the SOC is predominantly caused by the curvature of the molecule's surface [1]. [1] Dali Sun, Kipp J. van Schooten, Hans Malissa, Marzieh Kavand, Chuang Zhang, Christoph Boehme, and Z. Valy Vardeny, Nature Materials 15, 863-869 (2016). [Preview Abstract] |
Monday, March 13, 2017 9:48AM - 10:00AM |
A11.00008: Driving intramolecular charge transfer by tuning molecular orbitals and dielectric constants Melissa Aplan, Youngmin Lee, Jason Munro, Christopher Grieco, Zach Siebers, S. Michael Kilbey, Ismaila Dabo, Qing Wang, John Asbury, Enrique Gomez Fully conjugated block copolymers, consisting of an electron donor and an electron acceptor block, can serve as the active layer in organic photovoltaic devices. Incorporating the donor-acceptor interface within the chemical structure enables model studies of energy and charge transfer. We synthesized a series of block copolymers consisting of a P3HT electron donor and a push-pull polymer electron acceptor, either poly-2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopentadithiophene)-alt-[4,7-bis(3-dodecylylthiophen-5-yl)-2,1,3-benzothiadiazole]-2',2"-diyl) (PCPDT12BT), poly-((9-(9-heptadecanyl)-9H-carbazole)-1,4-diyl-alt-[4,7-bis(3-hexylthiophen-5-yl)-2,1,3-benzothiadiazole]-2',2"-diyl) (PCT6BT), poly-((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthiophen-5-yl)-2,1,3-benzothiadiazole]-2',2"-diyl) (PFT6BT), or poly-((2,5-dihexylphenylene)-1,4-diyl-alt-[4,7-bis(3-hexylthiophen-5-yl)-2,1,3-benzothiadiazole]-2',2"-diyl) (PPT6BT). By altering only the electron rich unit of the acceptor, we adjust the energy difference between the HOMO of the donor and acceptor by tenths of an eV. Absorption and emission spectra of the block copolymers enable us to quantify the yield of intramolecular charge transfer states in dilute solutions. We find a critical driving force required to generate CT states that depends on the dielectric constant of the solvent. [Preview Abstract] |
Monday, March 13, 2017 10:00AM - 10:12AM |
A11.00009: Hierarchical morphology to control energy and charge transfer in polymer blend light emitting diodes Keith Hillaire, Thomas Ferron, Michael Pope, Brian Collins With increasing efficiency, flexibility, and facile processing routes, organic light emitting diodes (OLEDs) are en route to replace their inorganic counterparts in lighting and displays. Blends of polymers can be used to enhance their performance and tune emissive colors in OLEDs through energy transfer to respective components. Nanostructure of those components is also important but has not been explored with as much detail. Here we use resonant and diffractive X-ray techniques to reveal the hierarchical morphology present in F8:F8BT polymer blend OLEDs. We find that energy and charge transfer processes resulting in photon emission are highly affected by the specific morphological state of the system, controlled by blend ratio and the concentration of processing additives. Such control over structure in OLEDs via simple processing variations will allow the tuning of optical and electronic performance in these novel devices. [Preview Abstract] |
Monday, March 13, 2017 10:12AM - 10:24AM |
A11.00010: Study on the optoelectronic proprieties and molecular structure of Alkyl-substituted Oligopyrrole for organic electronics Hussam Bouaamlat, Oufae Ninis, Mustapha Abarkan, Mohammed Bouachrine The investigation of 3,3'-dicotylterpyrrole (DOTP), 3,3'-dihexylquaterpyrrole (DH4P) and 3,7-dimethyldienyloctyl-3'dodecylquarterpyrrole (ddoD4P) both in doped and undoped forms was performed on the basis of density functional theory (DFT) at B3LYP and UB3LYP/6-31G* level of theory. Alkyl-substituted Oligopyrrole is unique due to the presence of the alkyl as terminal, the structural and electronic proprieties along with infra-red spectra was investigated. the change in geometric parameters, and HOMO, LUMO, Gap energies analysis provide an effective evidence and suggest these compounds as good candidates for optoelectronic applications. Further support to the previous proprieties electronic excited state energies was extract by TD//B3LYP/6-31G(d). gap decreases as the oligomer chain length increases, illustrating that how electronic properties can be tuned by the backbone ring or side group. The results became more sophisticated in the doped form of ddoD4P. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 10:36AM |
A11.00011: Band bending effect in P3HT: Role of morphology J. K. Wenderott, Ban X. Dong, Peter F. Green We utilized~Kelvin probe force microscopy (KPFM) to investigate band bending of~poly(3-hexylthiophene) (P3HT) films fabricated using both conventional spin-casting and the novel matrix assisted pulsed laser evaporation (MAPLE) technique on ITO:PEDOT substrates. Our findings show an association between band bending and out-of-plane transport characteristics of the films. A strong band bending effect is observed in MAPLE-deposited samples, whereas a weaker effect is seen in the spin-cast counterpart. With modeling, the charge transfer between the conductive ITO:PEDOT substrate and the MAPLE-deposited P3HT sample can be explained by a broadening of the density of states (DOS). This broadening likely originates from the highly disordered structure of MAPLE P3HT as reported in our previous study. Temperature dependence of the out-of-plane carrier mobility shows higher activation energy in the MAPLE-deposited sample as compared to spin-cast samples (180 meV versus 120 meV), which further corroborates the observed broadening of the DOS measured by KPFM. Our work indicates a strong connection between molecular structure, electronic states and bulk transport in conjugated polymer films. [Preview Abstract] |
Monday, March 13, 2017 10:36AM - 10:48AM |
A11.00012: Optical spectroscopy of two-dimensional polymer networks Halleh Balch, Christian Diercks, Peter Waller, Lei Guo, Michio Matsumoto, Raghunath Dasari, Seth Marder, Omar Yaghi, Will Dichtel, Feng Wang Two-dimensional covalent organic frameworks are periodic materials comprised of molecular monomers bound covalently in plane and pi-bonded out of plane. By leveraging the versatility of imine condensation reactions, we are able to employ a library of conjugated small molecules including porphyrins, fluorenes, pyrenes, and triphenylenes to develop extended structures. We study their optoelectronic properties via absorption, photoluminescence, and vibrational spectroscopy to understand how physical properties can be designed at the molecular- and emergent at the macroscopic-scale. [Preview Abstract] |
Monday, March 13, 2017 10:48AM - 11:00AM |
A11.00013: The isolated large $\pi $ systems in pyrene--fluorene derivatives observed with Scanning Tunneling Microscopy. Zongqiang Pang, Yue Zhang, Zhou Rong, Chao Tang The isolated large $\pi $ systems in pyrene-fluorene derivatives has been studied with Liquid Scanning Tunneling Microscopy (L-STM). From the Ultraviolet (UV) adsorption spectrum, we find that different pyrene-fluorene derivatives show substantial spectrum diversity. At ambient condition, we deposit different fluorene-pyrene derivatives on highly oriented pyrolytic graphite (HOPG) surface seperately. From STM results, we observe the strong interaction between different functional groups and main conjugate chains. Our results helps to understand the mechanism of spectrum difference between different pyrene-fluorene derivatives, and guide us to develop more efficient blue light emitting materials in nodoped Organic Light Emitting Diodes (OLEDs) , which is important for the industry of information displays. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700