Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L25: Chemical Physics of Multichromophores IVFocus
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Sponsoring Units: DCP Chair: Greg Scholes Room: 288 |
Wednesday, March 15, 2017 11:15AM - 11:51AM |
L25.00001: Molecular aggregates in cavities: topological phases and novel chemical reactivities. Invited Speaker: Joel Zhou In this talk, I will discuss the development of nontrivial topological phases in hybrid photon-exciton systems which gives rise to one-way robust energy transport in the presence of disorder. I will also discuss recent theoretical work discussing how thermodynamics and kinetics of molecular processes can be nontrivially altered when organic dye aggregates strongly interact with confined electromagnetic fields. I will discuss some generalizations of transition state theory that are suitable to polariton ensembles, and which may give rise to unprecedented control of chemical reactivity. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L25.00002: Electronic structure of electron donor-acceptor complexes in solution Carlos Diaz, Suhua Zhu, Tunna Baruah, Rajendra Zope We investigate the effect of solvent on the electronic structure of donor-acceptor complexes relevant in light harvesting. The model complexes we are studying are a porphyrin-fullerene dyad, a carotene-porphyrin-fullerene triad, a multichromophoric hexad molecule that consists of BDPY, Zn-tetraphenyl porphyrin, bis-phenyl anthracene, and fullerene. We first performed classical molecular dynamics simulation of the systems in explicit solvent. Subsequently, all-electron density functional calculations (DFT) using large basis sets is performed on the snap-shots taken from the molecular dynamics simulations. The solvents effects in the DFT calculations are treated using the explicit solvent or using their point charge representation. The effect of the solvents on the electronic properties will be discussed. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L25.00003: Metal Sulfide Nanocrystals inside Ferritin with Photovoltaic Applications Kameron Hansen, J Ryan Peterson, Cameron Olsen, Heather Hogg, John Colton, Richard Watt Ferritin is a spherical protein shell used universally by organisms to store iron. Due to a number of ferritin's properties (a conductive shell, ability to be arranged in ordered arrays, and high stability), recent theoretical work has proposed that non-native semiconductor nanocrystals inside ferritin can be used for high-efficiency solar energy conversion. We present research on the synthesis of a variety of these nanocrystals (PbS, CuS, Mo$_{\mathrm{2}}$S, ZnS, and PbSe) inside ferritin's hollow interior and band gap energies of the resulting ferritin-nanocrystal constructs. We also report preliminary solar cell results for dye sensitized solar cells with PbS-ferritin as the dye. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:51PM |
L25.00004: Sensitizing charge carrier generation in a conjugated polymer using a C70-encapsulated covalent organic polyhedron Invited Speaker: Garry Rumbles This presentation will report on the photophysics of a covalent organic polyhedron molecule (COP-5) containing two porphyrin molecules in the cage structure and with an encapsulated C70 molecule bound in its core. The photo-induced electron transfer processes in this structure create anomalously long-lived charge-transfer states that also respond to the dielectric constant of the solvent in an unconventional fashion. Preliminary results on using this complex to sensitize the production of long-lived charge carriers in a conjugated polymer will also be reported, where the carrier yields and kinetics are tracked using time-resolved microwave conductivity. The purpose of this work is to gain a better understanding of the nature of charge transfer (CT) and charge-separated (CS) states in the production of carriers in conjugated polymers blended with fullerenes. [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L25.00005: Vibrational Relaxation Description In the Coherent Domain and Inverted Temperature Dependence of Relaxation Rates Anastasia Ierides, Vasudev Kenkre The vibrational relaxation of molecules embedded in an environment is described in terms of a generalized master equation that is based on, but goes beyond, the well-known Montroll-Shuler equation$^1$ in chemical physics. Relaxation rates are calculated explicitly on the basis of our theory$^2$ for given microscopic Hamiltonians representing the molecule-bath interaction and the problem of “inverted temperature dependence” reported$^3$ in some observations is addressed. $[1]$ E. W. Montroll and K. E. Shuler, J. Chem. Phys. (1957). $[2]$ V. M. Kenkre and M. Chase. Preprint. $[3]$ A. Tokmakoff, B. Sauter, and M. D. Fayer. J. Chem. Phys. (1994). [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L25.00006: Singlet and quintet triplet pair states in organic singlet fission materials. Matthew Sfeir, Samuel Sanders, Murad Tayebjee, Elango Kumarasamy, Luis Campos, Dane McCamey We have recently demonstrated efficient intramolecular singlet fission (iSF) materials that achieve multiple exciton generation in isolated (i.e., in dilute solution) polymers and small molecules with multichromphore character. Still, fundamental questions remain concerning the electronic and mechanistic requirements that drive singlet fission in these materials, including the nature and dynamics of multiexciton (triplet pair) states. These iSF materials offer a unique platform in which to study the dynamical evolution of multiexciton states, since the system can be constrained such that exactly two triplet sites exist on the molecule. Using correlated ultrafast optical and electron spin resonance measurements, we identify long lived triplet pairs that exist in net singlet and net quintet spin multiplicities. We identify structure-function relationships that promote the dissociation of triplet pairs into free triplets and discuss implications for device applications. [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:51PM |
L25.00007: Understanding Non-Equilibrium Charge Transport and Rectification at Chromophore/Metal Interfaces Invited Speaker: Pierre Darancet Understanding non-equilibrium charge and energy transport across nanoscale interfaces is central to developing an intuitive picture of fundamental processes in solar energy conversion applications. In this talk, I will discuss our theoretical studies of finite-bias transport at organic/metal interfaces. First, I will show how the finite-bias electronic structure of such systems can be quantitatively described using density functional theory in conjunction with simple models of non-local correlations and bias-induced Stark effects. [1-6]. Using these methods, I will discuss the conditions of emergence of highly non-linear current-voltage characteristics in bilayers made of prototypical organic materials, and their implications in the context of hole- and electron-blocking layers in organic photovoltaic [7,8]. In particular, I will show how the use of strongly-hybridized, fullerene-coated metallic surfaces as electrodes is a viable route to maximizing the diodic behavior and electrical functionality of molecular components.~ References:~ [1] J.B. Neaton et al. Phys. Rev. Lett. 97, 216405 (2006); [2] I. Tamblyn,, et al. Phys. Rev. B, 84, 201402(R) (2011); [3] J. Widawsky, et al. Nano Letters 12, 354 (2012); [4] P. Darancet, et al. Nano Letters 12, 6250 (2012); [5] T. Kim, et al. Nano Letters ~2, 794 (2014); [6] B. Capozzi, et al. Nano Letters 3, 1400 (2014); [7] J.A. Smerdon, et al. Nano Letters 16, 2603 (2016) [8] J.A. Smerdon, et al. \textit{submitted} (2016). [Preview Abstract] |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L25.00008: Reversible Control of Surface-Spin-Trans-Effect and Molecular Kondo Resonance Studied Using Scanning Tunneling Microscopy and Spectroscopy Min Hui Chang, Yun Hee Chang, Howon Kim, Soon-Hyeong Lee, Un Seung Jeon, Kyung Min Kim, Mahn-Soo Choi, Yong-Hyun Kim, Se-Jong Kahng Metal-centered organometallic complexes form 6 coordinated structures having two out-of-plane bonds that competes each other; one of the two out-of-plane bonds that formed earlier than the other is weakened with an increased bond length by the formation of the other. This well-known trans-effect in chemistry, appeared recently on metal surfaces in spin versions in regard to the coordination reactions between small molecules and metallo-porphyrin. They were studied using averaging measurements such as X-ray photoelectron spectroscopy and magnetic circular dichroism, but rarely studied at the single molecule level. Here, we demonstrate that spin interactions in Co-porphyrin/Au(111) can be controlled by coordination and de-coordination of small molecules using scanning tunneling microscopy and spectroscopy (STM and STS). With small molecule coordination, we observed that a zero-bias peak at Co-porphryin, a signature of Kondo resonance in STS, switched off or remained but with a reduced width, i.e., Kondo temperature, and that it could be reversibly retrieved by single molecular STM manipulations. Based on our density functional theory calculation results, the reduced Kondo temperature is explained with the change in the unpaired spins in dz2 orbitals of Co-porphyrin by vertical small molecule coordination. [Preview Abstract] |
Wednesday, March 15, 2017 2:03PM - 2:15PM |
L25.00009: Characterizing the multiexciton fission intermediate in pentacene through 2D spectral modeling Roel Tempelaar, David Reichman Singlet fission, the molecular process in which a singlet excitation splits into two triplet excitons, holds promise to enhance the photoconversion efficiency of solar cells. Despite advances in both experiments and theory, a detailed understanding of this process remains lacking. In particular, the nature of the correlated triplet pair state (TT), which acts as a fission intermediate, remains obscure. Recently, 2D spectroscopy was shown to allow for the direct detection of the extremely weak optical transition between TT and the ground state through coherently prepared vibrational wavepackets in the associated electronic potentials. Here, we present a microscopic model of singlet fission which includes an exact quantum treatment of such vibrational modes. Our model reproduces the reported 2D spectra of pentacene, while providing a detailed insight into the anatomy of TT. As such, our results form a stepping stone towards understanding singlet fission at a molecular level, while bridging the gap between the wealth of recent theoretical works on one side and experimental measurements on the other. [Preview Abstract] |
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