Summary – Here, we obtain a 3.3 Å resolution structure of light-harvesting nanotubes derived from an amphiphilic cyanine dye (C8S3-Cl). The brick layer arrangement observed revises the previously hypothesized herringbone arrangement. This work shows how independently obtained native-state structures will enable accurate understanding of (excitonic) structure–function properties. Read more from the author here.
Summary – We demonstrate the preparation of mesoscale semiconductor (II–VI) nanoplatelets (NPLs) for the first time using colloidal seeded growth. These nanoplatelets are quantum-confined and atomically precise but grown to a length scale compatible with conventional optical imaging and microscopic manipulation (even reaching >1 μm2) offering an opportunity to bridge the application space between nanocrystals and two-dimensional (2D) materials.
C. D. Aiello, J. M. Abendroth, M. Abbas, A. Afanasev, S. Agarwal, A. S. Banerjee, D. N. Beratan, J. N. Belling, B. Berche, A. Botana, J. R. Caram, et al. “A Chirality-Based Quantum Leap” ACS Nano (2022).
Summary – Using experiment and theory, we formulate an energy gap master equation to explain the low quantum yields of organic chromophores with energy gaps in the SWIR. We also create an energy-gap-independent improvement factor, to determine the impact of synthetic modifications on parameters contributing to the quantum yield. We show that rational design changes based off EQME improved quantum yields.
C. E. Dickerson, H. Guo, G.-Z. Zhu, E. R. Hudson, J. R. Caram, W. C. Campbell, A. N. Alexandrova “Optical Cycling Functionalization of Arenes” J. Phys. Chem. Lett. 12 (16), 3989–3995 (2021).
Summary – In this work, the exciton binding energy of cadmium telluride and mercury chalcogenide nanoplatelets (NPLs) are reported for the first time, using the 3D Elliott formula to model low-resolution, high-throughput absorbance spectra. The effect of the external dielectric is also explored through an analytical model, which shows good agreement to our and previously reported values for CdSe NPL excitons– suggesting surface modification as a potential method to modulate photophysics and device properties.
C. D. Aiello, D. D. Awschalom, H. Bernien, T. Brower-Thomas, K. R. Brown, T. A. Brun, J. R. Caram, E. Chitambar, R. D. Felice, M. F. J. Fox et al. “Achieving a quantum smart workforce” Quantum Sci. Technol., 6, 030501 (2021).
Summary – We model the thermodynamic landscape that governs the self-assembly of cyanine dyes, providing a general approach to selectively make extended 2-dimensional J-aggregates. We show the universality of this approach by making J-aggregates of several sheet forming cyanine dyes with absorption tunability from visible through shortwave infrared.
M. Pengshung, P. Neal, T. L. Atallah, J. Kwon, J. R. Caram, S. A. Lopez, E. M. Sletten “Silicon incorporation in polymethine dyes” Chem. Commun., 56, 6110-6113 (2020).
Summary – We make two dimensional mercury chalcogenide nanoplatelets and induce room temperature growth of quantum dots on their surfaces through a ligand exchange procedure and control over excess QD precursors. Energy transfer from platelet to dot produces tunable SWIR emission with high quantum yields and fast radiative lifetimes.
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?.
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.
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,12 (5), 4556–4564 (2018). *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.
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.
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.
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.
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.
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.
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).
Caram Group 