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Synthesis and Photophysical Properties of Light-Harvesting Gold Nanoclusters Fully Functionalized with Antenna Chromophores
The development of efficient light-harvesting systems is important to understand the key aspects of solar-energy conversion processes and to utilize them in various photonic applications. In this study, atomically well-defined gold nanoclusters are reported as a new platform to fabricate artificial light-harvesting systems. An efficient amide coupling method is developed to synthesize water-soluble Au 22 clusters fully protected with pyrene chromophores by taking advantage of their facile phase-transfer reaction. The synthesized Au 22 clusters with densely packed 18 pyrene chromophores (Au 22 –PyB 18 ) exhibit triple-emission in blue, green, and red wavelength regions arising respectively from pyrene monomer, pyrene excimer, and Au 22 emission, producing bright white light emission together. The photoluminescence of Au 22 is enhanced by more than tenfold, demonstrating that pyrenes at the periphery efficiently channel the absorbed energy to the luminescent Au 22 at the center. A combination of femtosecond transient absorption and anisotropy measurements of Au 22 –PyB 18 explicitly reveals three main decay components of 220 fs, 3.5 ps, and 160 ps that can be assigned to energy migration between pyrenes and energy transfer processes from pyrene monomer and excimer to the central Au 22 , respectively.
Particle Response of Antenna-Coupled TES Arrays: Results from SPIDER and the Laboratory
Future mm-wave and sub-mm space missions will employ large arrays of multiplexed transition-edge-sensor (TES) bolometers. Such instruments must contend with the high flux of cosmic rays beyond our atmosphere that induce ‘glitches’ in bolometer data, which posed a challenge to data analysis from the Planck bolometers. Future instruments will face the additional challenges of shared substrate wafers and multiplexed readout wiring. Here, we explore the susceptibility of modern TES arrays to the cosmic ray environment of space using two data sets: the 2015 long-duration balloon flight of the SPIDER cosmic microwave background polarimeter, and a laboratory exposure of SPIDER flight hardware to radioactive sources. We find manageable glitch rates and short glitch durations, leading to minimal effect on SPIDER analysis. We constrain energy propagation within the substrate through a study of multi-detector coincidences and give a preliminary look at pulse shapes in laboratory data.
Recent Developments of Commercially Fabricated Horn Antenna-Coupled Transition-Edge Sensor Bolometer Detectors for Next-Generation Cosmic Microwave Background Polarimetry Experiments
Here we report on the successful fabrication of orthomode transducer-coupled transition-edge sensor (TES) bolometer arrays for cosmic microwave background (CMB) polarimetry experiments with the superconductor electronics fabrication facility at SEEQC Inc. Commercial microfabrication foundry could provide increase in detector fabrication throughput for a next-generation CMB experiment, CMB-S4, that would deploy approximately one order of magnitude more detectors than current CMB experiments. We also developed TES bolometers with two TESs in series that have two different superconducting temperatures (Tc) using a superconducting proximity effect between niobium (Nb) and aluminum-manganese (AlMn) alloy. We will discuss the motivation, design considerations, fabrication processes, test results, and how industrial detector fabrication could be a path to fabricate hundreds of detector wafers for future CMB polarimetry experiments and other experiments that require TESs and superconducting RF circuits.
Structure of the antenna complex expressed during far-red light photoacclimation in Synechococcus sp. PCC 7335
Far-red light photoacclimation, or FaRLiP, is a facultative response exhibited by some cyanobacteria that allows them to absorb and utilize lower energy light (700–800 nm) than the wavelengths typically used for oxygenic photosynthesis (400–700 nm). During this process, three essential components of the photosynthetic apparatus are altered: photosystem I, photosystem II, and the phycobilisome. In all three cases, at least some of the chromophores found in these pigment–protein complexes are replaced by chromophores that have red-shifted absorbance relative to the analogous complexes produced in visible light. Recent structural and spectroscopic studies have elucidated important features of the two photosystems when altered to absorb and utilize far-red light, but much less is understood about the modified phycobiliproteins made during FaRLiP. We used single-particle, cryo-EM to determine the molecular structure of a phycobiliprotein core complex comprising allophycocyanin variants that absorb far-red light during FaRLiP in the marine cyanobacterium Synechococcus sp. PCC 7335. The structure reveals the arrangement of the numerous red-shifted allophycocyanin variants and the probable locations of the chromophores that serve as the terminal emitters in this complex. It also suggests how energy is transferred to the photosystem II complexes produced during FaRLiP. The structure additionally allows comparisons with other previously studied allophycocyanins to gain insights into how phycocyanobilin chromophores can be tuned to absorb far-red light. These studies provide new insights into how far-red light is harvested and utilized during FaRLiP, a widespread cyanobacterial photoacclimation mechanism.
On the Red Antenna States of Photosystem I Mutants from Cyanobacteria Synechocystis PCC 6803
To identify the molecular composition of the low-energy states in cyanobacterial Photosystem I (PSI) of Synechocystis PCC6803, we focus on high resolution (low-temperature) absorption, emission, resonant, and nonresonant hole burned spectra obtained for wild-type (WT) PSI and three PSI mutants. In the Red_a mutant, the B33 chlorophyll (Chl) is added to the B31-B32 dimer; in Red_b, histidine 95 (His95) on PsaB (which coordinates Mg in the B7 Chl within the His95-B7-A31-A32- cluster) is replaced with glutamine (Gln), while in the Red_ab mutant, both mutations are made. We show that the C706 state (B31-B32) changes to the C710 state (B31-B32-B33) in both Red_a and Red_ab mutants, while the C707 state in WT Synechocystis (localized on the His95-B7-A31-A32 cluster) is modified to C716 in both Red_b and Red_ab. Excitation energy transfer from C706 to the C714 trap in the WT PSI and Red_b mutant is hampered as reflected by a weak emission at 712 nm. Large electron-phonon coupling strength (exposed via resonant hole-burned spectra) is consistent with a strong mixing of excited states with intermolecular charge transfer states leading to significantly red-shifted emission spectra. We conclude that excitation energy transfer in PSI is controlled by fine-tuning the electronic states of a small number of highly conserved red states. Finally, we show that mutations modify the protein potential energy landscape as revealed by different shapes and shifts of the blue- and red-shifted antiholes.
Ultrafast Collective Excited-State Dynamics of a Virus-Supported Fluorophore Antenna
Radiation brightening was recently observed in a multifluorophore-conjugated brome mosaic virus (BMV) particle at room temperature under pulsed excitation. On the basis of its nonlinear dependence on the number of chromophores, the origins of the phenomenon were attributed to a collective relaxation. However, the mechanism remains unknown. Here, we present ultrafast transient absorption and fluorescence spectroscopic studies which shed new light on the collective nature of the relaxation dynamics in such radiation-brightened, multifluorophore particles. Our findings indicate that the emission dynamics is consistent with a superradiance mechanism. The ratio between the rates of competing radiative and nonradiative relaxation pathways depends on the number of chromophores per virus. The findings suggest that small icosahedral virus shells provide a unique biological scaffold for developing nonclassical, deep subwavelength light sources and may open new avenues for the development of photonic probes for medical imaging applications.
Energy Transfer in Aqueous Light Harvesting Antennae Based on Brush-like Inter-Conjugated Polyelectrolyte Complexes
Conjugated polyelectrolytes (CPEs) have the potential to serve as building blocks of artificial light-harvesting systems. This is primarily due to their delocalized electronic states and potential for hierarchical self-assembly. We showed previously that inter-CPE complexes composed of oppositely charged exciton-donor and exciton-acceptor CPEs displayed efficient electronic energy transfer. However, near ionic charge equivalence, complexed CPE chains become net-neutral and thus experience a precipitous drop in aqueous solubility. To increase the stability and to rationally manipulate the phase behavior of inter-CPE complexes, we synthesized a series of highly water-soluble exciton-donor CPEs composed of alternating ionic and polar nonionic fluorene monomers. The nonionic monomer contained oligo(ethyleneglycol) sidechains of variable length. We then formed exciton donor-acceptor complexes and investigated their relative energy transfer efficiencies in the presence of a fixed exciton-acceptor CPE. We find that, even when the polar nonionic sidechains become quite long (nine ethyleneglycol units), the energy transfer efficiency is hardly affected so long as the inter-CPE network retains a net polyelectrolyte charge. However, near the onset of spontaneous phase separation, we observe a clear influence of the length of the oligo(ethyleneglycol) sidechains on the photophysics of the complex. Our results have implications for the use of polyelectrolyte phase separation to produce aqueous light-harvesting soft materials.
Imaging Strongly Coupled Plasmon–Phonon Modes in Mid-Infrared Double Antennas
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Coupling into Hyperbolic Carbon-Nanotube Films with a Deep-Etched Antenna Grating
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Electro-Absorptive Quantum Dot Antenna Resolves Terahertz Lightwaves via Biased Stark Effect
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