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Postdoctoral Work

E.M. Cosco, J. R. Caram O. T. Bruns, E. P. Farr, M. G. Bawendi, E. M. Sletten, ”Flavylium polymethine fluorophores are bright near- and shortwave infrared emitters.” Angewandte Chemie (2017) DOI: 10.1002/anie.201706974

J. A. Carr, D. Franke, J. R. Caram, C. F. Perkinson, V. Askoxylakis, M. Datta, D. Fukumura, R. K. Jain, M. G. Bawendi, O. T. Bruns. “Shortwave Infrared Fluorescence Imaging with the Clinically Approved Near-Infrared Dye Indocyanine green” Biorxiv

J. R. Caram, S. N. Bertram, H. Utzat, W. R. Hess, J. A. Carr, T. S. Bischof, A. P. Beyler, M. G. Bawendi ,”PbS Nanocrystal Emission is Governed by Multiple Emissive States.” Nano Lett., 2016, 16 (10), pp 6070–6077

pbspaperQuick Summary-PbS NCs show both “trap” and band-edge emissive character at room temperature.  Combining photon correlation Fourier spectroscopy with temperature dependent time resolved and static emission spectroscopy we build a model which demonstrates that these two states slowly interchange upon excitation over a kinetic barrier.  This can help explain trends in QD emission energy, quantum yield, and linewidth as a function of size and temperature.

J. R. Caram, S. Doria, D. M. Eisele, T. Sinclair, S. Lloyd, M. G. Bawendi, “Room Temperature Micron-Scale Exciton Migration in a Stabilized Emissive Molecular-Aggregate.” Nano Lett., 2016, 16 (11), pp 6808–6815

jaggQuick Summary– Light harvesting nanotubes are self-assembled J-Aggregates which have extended delocalized excitons.  We show that we can stabilize these aggregates to photodamage in a sugar based-matrix.  This has enabled detailed cryogenic spectroscopy, including exciton-exciton annihilation. Surprisingly, we observe signatures of exciton exciton annihilation that indicate extremely long exciton migration.  This exciton migration is mostly coherent, punctuated with transient localization by the environment.

T.S. Bischof, J. R. Caram, A.P. Beyler M. G. Bawendi,”Extracting the average single-molecule photoluminescence lifetime from an solution of chromophores” Optics Letters 2016 41 (20) pp. 4823-4826

Quick Summary-  A neat method paper which that we can directly extract the biexciton emission dynamics from dilute solutions of chromophores, by resolving the lifetime of individual photons from two photon detection events.  Code is available upon request.

I. Coropceanu, A. Rosinelli, J.R. Caram F. S. Freyria, M. G. Bawendi, Variable Thickness CdSe/CdS Nanorods with Unity Fluorescence Quantum Efficiency.  ACS Nano 2016, 10 (3), 3295–3301

Graduate Work

Thesis: “Dynamics of Electronic States Embedded in Complex Environments”  Published 2014.

H. Zheng,* J.R. Caram,*  P.D. Dahlberg, B.S. Rolczynski, S. Viswanathan, D.S. Dolzhnikov, A. Khadivi, D.V. Talapin, G.S. Engel. Dispersion-Free Continuum Two-Dimensional Electronic Spectrometer.  Applied Optics, 53, 19091917 (2014). *Co first authors

Quick Summary-  We developed a new all reflective two-dimensional spectrometer which uses angled mirrors to induce delays.  This approach lets you use extremely broadband continuum generated pulses for multidimensional spectroscopy, while avoiding dispersion.

J.R. Caram, H. Zheng, P.D. Dahlberg, B.S. Rolczynski, G.B. Griffin, D.S. Dolzhnikov, D.V. Talapin, G.S. Engel. Exploring size and state dynamics in CdSe quantum dots using two-dimensional electronic spectroscopy. J. Chem .Phys., 140, 084701 (2014)

J.R. Caram, H. Zheng, P.D. Dahlberg,B.S. Rolczynski, G.B. Griffin, A.F. Fidler, D.S. Dolzhnikov, D.V. Talapin, G.S. Engel. Persistent Interexcitonic Quantum Coherence in CdSe Quantum Dots. J. Phys. Chem. Lett., 5, 196-204 (2014).

jz-2013-02336t_0005Quick Summary– In 2DES, electronic quantum coherence manifestes as oscillations at at the energy difference between states.  We show that quantum coherence between the first two electronic excited state of CdSe QDs, indicating that quantum mechanical phase is maintained between electronic states for 100s of  femtoseconds.  In QD systems, a shared phonon bath correlates the phase of the carrier wavefunctions, maintaining coherence between states.

P.D. Dahlberg, A.F. Fidler, J.R. Caram, P.D. Long, G.S. Engel, “Energy Transfer Observed In Live Cells Using Two-Dimensional Electronic Spectroscopy.” J. Phys. Chem. Lett., 4, 3636-3640 (2013).

K.A. Fransted, J.R. Caram, D. Hayes, G.S. Engel, “Two-Dimensional Electronic Spectroscopy of Bacteriochlorophyll a in Solution: Elucidating the Coherence Dynamics of the FennaMatthews-Olson Complex Using its Chromophore as a Control.” J. Chem. Phys., 137, 125101 (2012).

J.R. Caram, A.F. Fidler, G.S. Engel, “Excited and Ground State Vibrational Dynamics Revealed by Two Dimensional Electronic Spectroscopy.” J. Chem. Phys., 137, 024507 (2012). 20 most read in 2012 and Editors Choice 2012

A.F. Fidler, J.R. Caram, D. Hayes, G.S. Engel, “Toward a Coherent Picture of Excitonic Coherence in the Fenna-Matthews-Olson Complex.” J. Phys. B, 45, 154013 (2012).

J.R. Caram, N.H.C. Lewis, A.F. Fidler, G.S. Engel , “Signatures of Correlated Excitonic Dynamics in Two Dimensional Spectroscopy of the Fenna-Matthew-Olson Photosynthetic Complex.” J. Chem. Phys., 136, 104505 (2012). Selected for Virtual Journal of Biological Physics

Quick Summary– The origin of long-lived observed coherent oscilliations in spectra of photosynthetic antenna proteins remains somewhat controversial. In this paper we apply a new signal processing tool, the linear prediction z-transform, to map coherent signals in 2D-spectra, according to decay rates, frequencies, and phase.  We discuss how observation of long-lived coherences can be explained by invoking a correlated environment (bath).

J.R. Caram, G.S. Engel , “Extracting Dynamics of Excitonic Coherences in Congested Spectra of Photosynthetic Light Harvesting Antenna Complexes.” Faraday Discuss., 153(1), 93-104 (2011).

G. Panitchayangkoon, D.V. Voronine, D. Abramavicius, J.R. Caram, N. Lewis, S. Mukamel, G.S. Engel, “Direct Evidence of Quantum Transport in Photosynthetic Light-harvesting Complexes.” Proc. Natl. Acad. Sci.,108(52), 20908-20912 (2011).

D. Hayes, G. Panitchayangkoon, K.A. Fransted, J.R. Caram, J. Wen, K.F. Freed, G.S. Engel, “Dynamics of Electronic Dephasing in the Fenna-Matthews-Olson Complex.” New J. Phys, 12, 065042 (2010).

G. Panitchayangkoon, D. Hayes, K.A. Fransted, J.R. Caram, E. Harel, J. Wen, R.E. Blankenship, G.S. Engel, “Long-Lived Quantum Coherence in Photosynthetic Complexes at Physiological Temperature.” Proc. Natl. Acad. Sci., 107:29, 12766-12770, (2010).

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