Publications

Google Scholar

Since starting at UCLA

C. Chuang, D. I. G. Bennet, J.R Caram, A. Aspuru-Guzik, M. G. Bawendi, J. Cao ” Generalized Kasha’s Model: T-Dependent Spectroscopy Reveals Short-Range Structures of 2D Excitonic Systems” Chem DOI: 10.1016/j.chempr.2019.08.013 (2019) (Contact the PI for a PDF copy)

Arxiv Preprint: arxiv.org/abs/1901.01318

T. Atallah, A. Sica, A. Shin, H. Friedman J.R Caram. ” Decay Associated Fourier Spectroscopy: Visible to Shortwave Infrared Time-Resolved Photoluminescence Spectra” J. Phys. Chem. A 123 (31), 6792-6798 (2019)

Quick Summary-Check out our paper on Decay Associate Fourier Spectroscopy (DAFS) technique developed in the #CaramLab. Our DAFS method uses a Mach-Zehnder interferometer to record spectrally and temporally resolved photoluminescence in the Fourier domain (like FT-IR), allowing the setup to resolve weak emission signals from the background, even if system is fluctuating. Employing silicon avalanche photodiodes and superconducting nanowires in concert we achieve single photon sensitivity from the shortwave infrared (SWIR, 2 μm) through visible (400 nm) wavelengths. Our paper using two Förster resonance energy transfer pairs to show the efficacy of the DAFS. What will the #CaramLab do next with DAFS?.

abstractimagelocaliz

A. Deshmukh, D. Koppel, C. Chuang, D. Cadena, J. Cao, J.R. Caram. ” Design Principles for Two-Dimensional Molecular Aggregates Using Kasha’s Model: Tunable Photophysics in Near and Short-Wave Infrared ” J. Phys. Chem. C 123 (30), 18702-18710 (2019)

Quick Summary– We make molecular aggregates with strong SWIR absorption and show that we can chemically control their photphysics by changing the supramolecular arrangement of the chromophores within the aggregate. We also find a new aggregate type called as ‘I-aggregate’ which has combined features of the well-known H- and J-aggregates.

abstractimagelocaliz

S.N. Bertram , B. Spokoyny, D. Franke, J. R. Caram, J.J. Yoo, R.P. Murphy, M.E. Grein, M.G. Bawendi. “Single Nanocrystal Spectroscopy of Shortwave Infrared Emitters”  ACS Nano, 13 (2), pp 1042-1049 (2019)

S. Doria, A. Lapini, M. D. Donato, R. Righini, N. Azzaroli, A Iagatti, J. R. Caram, T.S. Sinclair, L. Cupellini, S. Juronovich, B. Menucci, G. Zanotti, A.M. Paoletti, G. Pennesi, P. Foggi. ”Understanding the influence of disorder on the exciton dynamics and energy transfer in Zn-phthalocyanine H-aggregates” Phys.Chem. Chem. Phys., 20, 22331-22341 (2018)

K. E. Shulenberger, T. S. Bischof, J. R. Caram, H. Utzat, I. Coropceanu, L. Nienhaus, M. G. Bawendi.  ”Multiexciton Lifetimes Reveal Triexciton Emission Pathway in CdSe Nanocrystals” Nano Lett, 18 (8), pp 5153-5158 (2018)

S. Doria, T. S. Sinclair, N. D. Klein, D. I. G. Bennett, C. Chuang, F. S. Freyria, C. P. Steiner, P. Foggi, K. A. Nelson, J. Cao, A. Aspuru-Guzik, S. Lloyd, J. R. Caram,* M. G. Bawendi. “Photochemical Control of Exciton Superradiance in Light-Harvesting Nanotubes” ACS Nano, Article ASAP DOI: 10.1021/acsnano.8b00911* Corresponding Author (2018)

Quick Summary– In this work we show that intense illumination actually changes the disorder and connectivity in a molecular aggregate, modulating exciton delocalization and superradiance. This shows that we can achieve chemical control over coherence in transition dipole moments.

abstractimagelocaliz

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” Proc. Natl. Acad. Sci.,  (2018)

B.S. Rolczynski, H. Zheng, V. P. Singh, P. Navotnaya, A. R. Ginzburg, J. R. Caram, K. Ashraf, A. T. Gardiner, S.-H. Yeh, S. Kais, R. J. Cogdell, G. S. Engel. Correlated Protein Environments Drive Quantum Coherence Lifetimes in Photosynthetic Pigment-Protein Complexes, Chem, 4, 1,  pp. 138-149, 11 (2018)

F. S. Freyria J. M. Cordero, J. R. Caram, S. Doria, A. Dodin, Y. Chen, A. P. Willard, and M. G. Bawendi, “Near-Infrared Quantum Dot Emission Enhanced by Stabilized Self-Assembled J-Aggregate Antennas” Nano Lett.,  17 (12), pp. 7665–7674 (2017)

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,129 (42), pp. 13306-13309

nature24755-f1

Paper Feature- Dr. Martin Schnerman profiled our work on SWIR emitting chromophores in Nature.

Postdoctoral Work

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., 16 (10), pp 6070–6077 (2017)

pbspaper

Quick 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., 16 (11), pp 6808–6815 (2016)

jagg

Quick 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 41 (20) pp. 4823-4826 (2016)

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,10 (3), 3295–3301 (2016)

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_0005

Quick 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).

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s