Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G05: Electronic-Vibrational Coupling in Light Harvesting II. Excitons, Polarons, Perovskites, and Non-Adiabatic DynamicsFocus
|
Hide Abstracts |
Sponsoring Units: DCP DAMOP DCMP DPOLY Chair: David Jonas, University of Colorado, Boulder Room: 111 |
Tuesday, March 3, 2020 11:15AM - 11:51AM |
G05.00001: Excitons and Polarons in Organic Materials Invited Speaker: Frank Spano Excitons and polarons play a critical role in the electronic properties of organic molecular aggregates as well as conjugated polymers and aggregates thereof. For many conjugated organic molecules neutral excitations (excitons) and charged excitations (polarons) are coupled strongly to nuclear degrees of freedom involving the symmetric vinyl-stretching mode (i.e. the aromatic-quinoidal vibration when conjugated rings are present). In this talk the photophysical properties of excitons and polarons in conjugated organic materials are compared and contrasted within the framework of a theory based on the Holstein Hamiltonian, which treats local electron-vibrational coupling exactly. Applications are made to excitons in perylene diimide crystals [1] and dopant-induced positively-changed polarons (holes) in poly(3-hexylthiophene) films. [2,3 ] It is shown how simple optical probes like steady-state absorption and photoluminescence can be used to extract the exciton and polaron coherence lengths, quantities which are important for understanding energy and charge transport. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G05.00002: Spectral Signatures and Spatial Coherence of Bound and Unbound Polarons in Organic Semiconductors: Theory vs Experiment Raja Ghosh, Christine Luscombe, Salleo Alberto, Frank Spano The spectral line-shape of the mid-IR absorption spectrum provides valuable information about the “hole” polaron coherence length in doped and undoped conjugated polymer films. Using a theory based on the Holstein Hamiltonian for mobile holes in P3HT, the IR line-shape is successfully reproduced for several recently measured spectra recorded in doped and undoped films, confirming the association of an enhanced peak ratio (A/B) with extended polaron coherence. Emphasis is placed on the origin of components polarized along the intra- and inter-chain directions and their dependence on the spatial distribution of disorder and the position of the dopant relative to the π-stack. The model has been further adapted to treat donor-acceptor copolymers. |
Tuesday, March 3, 2020 12:03PM - 12:39PM |
G05.00003: Correlating Structure and Function in Two-Dimensional Organic-Inorganic Hybrid Perovskites Invited Speaker: Cherie Kagan Two-dimensional, organic-inorganic hybrid perovskites (2DHPs) are stoichiometric compounds composed of alternating sheets of corner-sharing, metal-halide octahedra and organoammonium cationic layers. We study 2DHPs containing single lead iodide layers separated by intervening substituted, phenethylammonium cations with the chemical structure (x-PEA)2PbI4, where x=F, Cl, Br, or CH3. These 2DHPs form type-I heterojunctions in which excitons and carriers are confined to the lead halide layers and strong quantum and dielectric confinement effects establish exciton binding energies that exceed 150 meV. We use powder and single-crystal x-ray diffraction studies, in combination with variable-temperature, steady-state and time-resolved absorption and photoluminescence (PL) measurements to uncover the correlation between their structure and photophysical properties. 15 K spectra of unsubstituted (PEA)2PbI4 show splitting of the excitonic absorption and PL into regularly spaced resonances every 40-46 meV. In addition, anti-Stokes hot exciton PL is observed at the same energy as optical absorption resonances. Substitution on the organic cations, for example in the para position, increases the length of the organic cation and therefore the interlayer spacing, but leaves the cross-sectional area for the organic cation unchanged and results in structurally similar metal halide frameworks. As the length of the cation increases in the 2DHP, the absorption spectra broaden and blueshift, but the PL spectra remain invariant. We show that the excitonic structure is consistent with strong electron-phonon coupling and slow vibrational relaxation originating from the softness of the metal halide framework and the organic cations. |
Tuesday, March 3, 2020 12:39PM - 12:51PM |
G05.00004: Investigating how biological membrane parameters influence the ring opening of Provitamin D Danielle Sofferman, Roseanne J Sension Ultrafast photochemical transformations of 7-Dehydrocholesterol (DHC, Provitamin D3), DHC-Acetate and Ergosterol (Ergo, Provitamin D2) to previtamin (D3, D3-acetate and D2) occurs upon a ring-opening reaction in the excited state where a Cyclohexadiene (CHD) chromophore embedded within the molecules opens to form a previtamin D species. In isotropic environments, the ring opening reaction occurs within 1-2ps therefore it is necessary to use ultrafast techniques such as transient absorption to capture the kinetics. However, in the lipid bilayer this reaction is slowed to 11ps. Here we are studying DHC and its analogs in lipid bilayers as a simple model for biologically relevant skin membrane models. To investigate the 6 fold slow down, the ring opening of DHC will be discussed in terms of lipid properties such as Van der Waals interactions, Hydrogen Bonding and membrane ridgidity. |
Tuesday, March 3, 2020 12:51PM - 1:27PM |
G05.00005: Superradiance of two-dimensional molecular aggregates Invited Speaker: Alex Eisfeld Assemblies of molecules (so-called molecular aggregates) have become versatile quantum systems with applications in photography, opto-electronics, solar cells, and photo-biology. The remarkable properties of these aggregates stem from the strong transition dipole-dipole interaction between the individual molecules which leads to eigenstates with excitation shared coherently by a large number of molecules. As a consequence the aggregate possesses strikingly different optical properties compared to the individual molecules. |
|
G05.00006: Resonant confinement of an excitonic polariton and ultra-efficient light harvest in artificial photosynthesis Yong-Cong CHEN, Bo Song, Anthony J Leggett, Ping Ao, Xiaomei Zhu We uncover a novel phenomenon from a recent artificial light-harvesting experiment [Angewandte Chemie Intl. Ed. 55, 2759 (2016)] on organic nanocrystals of self-assembled difluoroboron chromophores. |
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