Rapid Energy Transfer Research Articles

Effective Light-Harvesting Antennae Based on BODIPY-Tethered Cardo Polyfluorenes via Rapid Energy Transferring and Low Concentration Quenching

Light-harvesting antennae (LHA) were demonstrated using polyfluorenes (PFs) modified with borondipyrromethene (BODIPY) dyes tethered to the cardo structures. PFs work as a light absorber and an energy donor to the BODIPY units. The series of BODIPY-tethering PFs via the cardo carbon including homocardo PFs and alternative polymers with fluorene and the cardo fluorene were synthesized, and their optical properties were investigated. Initially, highly efficient energy transferring was observed from the PF main chains to the BODIPY unit (99%). It was found that PFs can work as an efficient light absorber because of the large molar extinction coefficient and cause the rapid energy transfer through the cardo structure. Next, from the comparison with the emission efficiency of the BODIPY units in the series of the synthetic polymers, the favorable position of the BODIPY units was obtained to avoid the concentration quenching: The alternative polymer with cardo fluorene and dialkyl-substituted fluorene showed th...

Density-dependent response of an ultracold plasma to few-cycle radio-frequency pulses

Ultracold neutral plasmas exhibit a density-dependent resonant response to applied radio-frequency (rf) fields in the frequency range of several to hundreds of megahertz for achievable densities. We have conducted measurements where short bursts of an rf fieldwere applied to these plasmas, with pulse durations as short as two cycles. We still observed a density-dependent resonant response to these short pulses, but the time scale of the response is too short to be consistent with local heating of electrons in the plasma from collisions under a range of experimental parameters. Instead, our results are consistent with rapid energy transfer to individual electrons from electric fields resulting from an overall displacement of the electron cloud from the ions during the collective motion of the electrons. This collective motion was also observed by applying two sharp electric field pulses separated in time to the plasma. These measurements demonstrate the importance of collective motion in the energy transport in these systems.

Photoalignment Layers for Liquid Crystals from the Di-π-methane Rearrangement

Photoalignment of nematic liquid crystals is demonstrated using a di-π-methane rearrangement of a designed polymer. The alignment mechanism makes use of the strong coupling of the liquid crystal directors to dibenzobarrelene groups. The large structural changes that accompany photoisomerization effectively passivate segments of the polymer, allowing the remaining dibenzobarrelene groups to dominate the director alignment. Photoisomerization requires triplet sensitization, and the polymer was designed to have a uniaxially fixed rigid structure and rapid triplet energy transfer from the proximate benzophenone units to the dibenzobarrelene groups. The isomerization was observed to be regiospecific, and thin films showed alignment.

Rapid energy transfer in non-porous metal–organic frameworks with caged Ru(bpy)32+ chromophores: oxygen trapping and luminescence quenching

Two non-porous metal–organic frameworks (MOFs) with caged Ru(bpy)32+ chromophores, [Ru(bpy)3][Zn2(C2O4)3] (1) and [Ru(bpy)3][NaAl(C2O4)3] (2), were synthesized and characterized. Their emission properties were studied by both steady-state and time-resolved luminescence measurements. Air-free microcrystals of 1 and 2 exhibit long-lived triplet metal-to-ligand charge transfer (3MLCT) excited states with lifetimes of 760 and 1305 ns, respectively. Lifetimes are significantly shortened (to 92 ns for 1 and 144 ns for 2) by trapping of trace amounts of oxygen in the non-porous MOFs, presumably due to amplified luminescence quenching of Ru(bpy)32+*. Following MLCT excitation, Ru(bpy)32+*/Ru(bpy)32+ energy transfer migration in 1 and 2 results in efficient quenching of Ru(bpy)32+* by Os(bpy)32+ added as an energy transfer trap at doping levels of 0.2–1.0%. A kinetic analysis indicates that the three-dimensional chromophore connectivity in 1 and 2 provides a network for rapid excited state energy transfer migration among Ru(bpy)32+ units, ultimately, finding an Os(bpy)32+ trap site. These crystalline frameworks with caged chromophores have proven to be ideal systems for studying light harvesting processes in artificial supramolecular systems.

NaYF4:Yb3+/Er3+ nanoparticle-based upconversion luminescence resonance energy transfer sensor for mercury(ii) quantification

Upconversion luminescence is an anti-Stokes' emission process by converting long wavelength near-infrared (NIR, 980 nm) irradiation into shorter wavelength visible light emission, which demonstrates many advantages including no autofluorescence, low damage to samples, no photobleaching, and high sensitivity. Based on the Rhodamine B thiolactone (RBT) functionalized NaYF(4):15%Yb(3+),5%Er(3+) (UCNPs@RBT) nanocomposites, an ultrasensitive, selective, and rapid upconversion luminescence resonance energy transfer (UC-LRET) sensor has been developed for the detection of mercury ions (Hg(2+)) in water. Upconverting luminescence resonance energy transfer from the UCNPs to the RBT derivates occurs after the addition of Hg(2+) ions into the UCNPs@RBT colloidal solution. This UC-LRET recognition of Hg(2+) can be finished within 1 min and other cations have no influence on the detection of mercury ions. This newly developed sensor demonstrates high selectivity toward the mercury ions and enables ultrasensitive and rapid detection of mercury ions in water in the range of 5 nM to 10 μM with a 3σ limit of detection of 3.7 nM. This sensor can be used for a naked-eye detection of Hg(2+) ions via its green upconverting luminescence response under the infrared excitation (980 nm) with the merit of no autofluorescence interference and good photostability. In addition, by dipping the hydrogel of UCNPs@RBT nanocomposites onto the filter paper, a highly selective and convenient luminescent paper sensor for Hg(2+) ions was also developed.

Self‐Assembled Bilayer Films of Ruthenium(II)/Polypyridyl Complexes through Layer‐by‐Layer Deposition on Nanostructured Metal Oxides

Simple assembly: A “layer-by-layer” deposition of functionalized dyes/catalysts on the surfaces of nanocrystalline oxides is introduced. The strategy is general and offers considerable flexibility based on phosphonate- or carboxylate-binding groups with ZrIV as bridging ions. The resulting bilayer structures are capable of supporting rapid intra-layer energy and electron transfer (see picture).

Microwave Assisted Synthesis of Poly(lactic acid) and its Characterization using Size Exclusion Chromatography

Poly(lactic acid) (PLA) has been synthesized catalytically under vacuum by microwave (MW) irradiation using stannous octoate (SnOct2) as catalyst. The polymerization is carried out at 180○C up to 30 min. PLA with a molar mass of 104 g.mol−1 and a yield over 97% was produced in 20 min by the ring-opening polymerization of L-lactide using (SnOct2) as catalyst under microwave irradiation with a power level of 180 W. The structural investigations are done by NMR and FTIR. The average molar mass of PLA is determined by means of size exclusion chromatography, (SEC). The characterization is done using three different columns. The polymerization rate is much faster with microwave heating than conventional heating. Microwave irradiation gives rapid energy transfer and high-energy efficiency, hence, a faster reaction rate.

Acoustic energy dissipation and thermalization in carbon nanotubes: Atomistic modeling and mesoscopic description

The exchange of energy between low-frequency mechanical oscillations and high-frequency vibrational modes in carbon nanotubes (CNTs) is a process that plays an important role in a range of dynamic phenomena involving the dissipation of mechanical energy in both individual CNTs and CNT-based materials. The rates and channels through which acoustic energy deposited instantaneously in individual CNTs is dissipated are investigated in a series of atomistic molecular dynamics simulations. Several distinct regimes of energy dissipation, dependent on the initial stretching or bending deformations, are established. The onset of axial or bending buckling marks the transition from a regime of slow thermalization to a regime in which the energy associated with longitudinal and bending oscillations is rapidly damped. In the case of stretching vibrations, an intermediate regime is revealed in which dynamic coupling between longitudinal vibrational modes and the radial ``squash'' mode causes delayed axial buckling followed by a rapid transfer of energy to high-frequency vibrations. The results of the atomistic simulations are used in the design and parameterization of a ``heat bath'' description of thermal energy in a mesoscopic model, which is capable of simulating systems consisting of thousands of interacting CNTs. Two complementary methods for the description of mechanical energy dissipation in the mesoscopic model are developed. The relatively slow dissipation of acoustic vibrations in the absence of buckling is described by adding a damping force to the equations of motion of the dynamic elements of the mesoscopic model. The sharp increase in the energy dissipation rate at the onset of buckling is reproduced by incorporating a hysteresis loop into the strain energy that accounts for localized thermalization in the vicinity of buckling kinks. The ability of the mesoscopic model to reproduce the complex multistep processes of acoustic energy dissipation predicted by the atomistic simulations is demonstrated in mesoscopic simulations of free stretching and bending vibrations of individual CNTs.

Direct imaging of the electronic dephasing in benzene: Experimental evidence for ultrafast intersystem crossing ofT3←S2states

The electronic dephasing of benzene on the second excited state has been observed using a femtosecond time-resolved photoelectron imaging technique coupled with time-resolved mass spectroscopy. Upon absorption of two 400-nm photons, benzene is excited to the S-2 state, and the time evolution of the parent ion can be well described by a biexponential decay: a rapid dephasing pathway with 43 fs and a longer-lived channel with 1.06 ps. The fast dephasing is ascribed to the internal conversion through the S-2-S-1 conical intersections, and the slower one is attributed to the intersystem crossing from the S-2 state. It is possible that the vibrational excitation modes (9(0)(1)16(1)(1), 5(0)(1), and 9(0)(1)) from the S-2 state enhance the spin-orbit coupling greatly, which leads to the S-2-T-3 intersystem crossing. The photoelectron kinetic energy distributions between 1.1 and 1.7 eV exhibit a rapid energy transfer, revealing nuclear motion on the S-2 adiabatic surface.

An approach to increase apparent damping with reduced subordinate oscillator array mass

The case of a lightly damped oscillator (primary mass) adorned with a set of substantially less massive oscillators is known as a subordinate oscillator array (SOA). An SOA can function as an energy sink on the primary, extracting vibration energy from it, thus adding apparent damping to the system. Low apparent Q is achieved by increasing non-dimensional bandwidth, which is the ratio of the bandwidth to the fundamental frequency of the primary. The mass of the subordinate set required to achieve the most rapid energy transfer from the primary is proportional to non-dimensional bandwidth squared. We have shown the limit of apparent damping achievable in these systems is the inverse of non-dimensional bandwidth. In practice, the utility of this result is limited because a great deal of mass (~30% of primary) is required to increase the apparent damping in the system such that Q_apparent→1. This work will focus on an alternative design strategy that produces comparable increase in apparent damping with less added mass. We describe numerical optimizations in which the non-dimensional bandwidth of the isolated natural frequencies of the SOA elements and the distribution of those isolated natural frequencies are used to minimize the total mass of the SOA.

Amplified Luminescence Quenching of Phosphorescent Metal–Organic Frameworks

Amplified luminescence quenching has been demonstrated in metal-organic frameworks (MOFs) composed of Ru(II)-bpy building blocks with long-lived, largely triplet metal-to-ligand charge-transfer excited states. Strong non-covalent interactions between the MOF surface and cationic quencher molecules coupled with rapid energy transfer through the MOF microcrystal facilitates amplified quenching with a 7000-fold enhancement of the Stern-Völmer quenching constant for methylene blue compared to a model complex.

A guide to RBF-generated finite differences for nonlinear transport: Shallow water simulations on a sphere

The current paper establishes the computational efficiency and accuracy of the RBF-FD method for large-scale geoscience modeling with comparisons to state-of-the-art methods as high-order discontinuous Galerkin and spherical harmonics, the latter using expansions with close to 300,000 bases. The test cases are demanding fluid flow problems on the sphere that exhibit numerical challenges, such as Gibbs phenomena, sharp gradients, and complex vortical dynamics with rapid energy transfer from large to small scales over short time periods. The computations were possible as well as very competitive due to the implementation of hyperviscosity on large RBF stencil sizes (corresponding roughly to 6th to 9th order methods) with up to O(105) nodes on the sphere. The RBF-FD method scaled as O(N) per time step, where N is the total number of nodes on the sphere. In Appendix A, guidelines are given on how to chose parameters when using RBF-FD to solve hyperbolic PDEs.

Correlated AFM-Spectroscopy Imaging of Linear Light Harvesting Protein Aggregates in Bacterial Native Photosynthetic Membrane

How light energy is harvested in a natural photosynthetic membrane through energy transfer is closely related to the stoichiometry and arrangement of light harvesting antenna proteins in the membrane. The specific photosynthetic architecture facilitates a rapid and efficient energy transfer among the light harvesting proteins (LH2 and LH1) and to the reaction center. Here we report the identification of linear aggregates of light harvesting proteins, LH2, in the photosynthetic membranes under ambient conditions by using atomic force microscopy (AFM) imaging and spectroscopic analysis. Our results suggest that the light harvesting proteins, LH2, can exist as linear aggregates of 2 to 8 proteins in the photosynthetic membranes, and the protein distributions are highly heterogeneous. LH2 antenna proteins are responsible for absorbing most of the light energy for photosynthesis, and efficient intra- and inter-molecular energy transfers of LH2 complexes are important for the overall efficiency of the light harvesting mechanism. We combined AFM imaging and spectroscopic analysis with J aggregate theoretical calculations to characterize the linear aggregation of LH2. AFM images reveal the linear aggregation of LH2, where the LH2 complexes are tilted to the plane of the photosynthetic membrane. The spectroscopic results support the attribution of LH2 complexes in the membrane to linear aggregates. The calculated values for the absorption, emission and lifetime using a model developed from J aggregate theory are consistent with the experimentally determined spectroscopic values, further proving a J type aggregation of the LH2 complexes in the photosynthetic membrane.

Efficient Intrinsic Photoprotection in Strongly Coupled (Bacterio) Chloropyll Complexes

Chlorophyll (Chl) molecules in photosynthetic proteins are known to produce highly toxic singlet oxygen under illumination as a result of energy transfer from their triplet excited states to oxygen. To prevent the formation of singlet oxygen, carotenoids (Car) are typically positioned close to Chl to ensure rapid triplet-triplet energy transfer from Chl to Car, which can then safely dissipate the energy of the excited states. Our recent studies revealed a new, unconventional, but very efficient photoprotection mechanism in strongly coupled natural and artificial light-harvesting complexes that does not rely on the presence of carotenoids. Experimental studies on carotenoid-free chlorosomes and artificial bacteriochlorophyll (BChl) aggregates show that these structures are at least three orders of magnitude more stable to photodamage than monomeric forms of BChl. It was proposed that this photoprotection in strongly coupled arrays of pigments is due to triplet exciton formation, which lowers the energy of the triplet exciton substantially below that of singlet oxygen.In this report we present the results of our ongoing comprehensive study of the properties of triplet excited states of monomeric BChls, Chl aggregates and chlorosomes by means of EPR, time-resolved optical pump-probe spectroscopy and steady-state IR phosphorescence spectroscopy.

Ultrafast vibrational energy transfer at the water/air interface revealed by two-dimensional surface vibrational spectroscopy

Water is very different from liquids of similar molecular weight, and one of its unique properties is the very efficient transfer of vibrational energy between molecules, which arises as a result of strong dipole-dipole interactions between the O-H oscillators. Although we have a sound understanding of such energy transfer in bulk water, we know less about how, and how quickly, transfer occurs at its interface with a hydrophobic phase, because specifically addressing the outermost monolayer is difficult. Here, we use ultrafast two-dimensional surface-specific vibrational spectroscopy to probe the interfacial energy dynamics of heavy water (D(2)O) at the water/air interface. The measurements reveal the presence of surprisingly rapid energy transfer, both between hydrogen-bonded interfacial water molecules (intermolecular), and between O-D groups sticking out from the water surface and those located on the same molecule and pointing towards the water bulk (intramolecular). Vibrational energy transfer occurs on sub-picosecond timescales, and its rates and pathways can be quantified directly.

Influence of temperature on thymine-to-solvent vibrational energy transfer

At the instant following the non-radiative deactivation of its ππ* electronic state, the vibrational modes of thymine possess a highly non-equilibrium distribution of excitation quanta (i.e., >4 eV in excess energy). Equilibrium is re-established through rapid (5 ps) vibrational energy transfer to the surrounding solvent. The mechanisms behind such vibrational cooling (VC) processes are examined here using femtosecond transient grating and two-dimensional photon echo spectroscopies conducted at 100 K and 300 K in a mixture of methanol and water. Remarkably, we find that this variation in temperature has essentially no impact on the VC kinetics. Together the experiments and a theoretical model suggest three possible mechanisms consistent with this behavior: (i) vibrational energy transfer from the solute to solvent initiates (directly) in intramolecular modes of the solute with frequencies >300 cm(-1); (ii) the relaxation induced increase in the temperature of the environment reduces the sensitivity of VC to the temperature of the equilibrium system; (iii) the time scale of solvent motion approaches 0.1 ps even at 100 K. Mechanism (i) deserves strong consideration because it is consistent with the conclusions drawn in earlier studies of isotope effects on VC in hydrogen bonding solvents. Our model calculations suggest that mechanism (ii) also plays a significant role under the present experimental conditions. Mechanism (iii) is ruled out on the basis of long-lived correlations evident in the photon echo line shapes at 100 K. These insights into photoinduced relaxation processes in thymine are made possible by our recent extension of interferometric transient grating and photon echo spectroscopies to the mid UV spectral region.

A rapid, sensitive, and selective bioluminescence resonance energy transfer (BRET)-based nucleic acid sensing system

Here we report the design of a bioluminescence resonance energy transfer (BRET)-based sensing system that could detect nucleic acid target in 5 min with high sensitivity and selectivity. The sensing system is based on adjacent binding of oligonucleotide probes labeled with Renilla luciferase (Rluc) and quantum dot (Qd) on the nucleic acid target. Here Rluc, a bioluminescent protein that generates light by a chemical reaction, is employed as an energy donor, and a quantum dot is used as an energy acceptor. Bioluminescence emission of Rluc overlaps with the Qd absorption whereas the emission of Qd is shifted from the emission of Rluc allowing for monitoring of BRET. In the presence of target, the labeled probes bind adjacently in a head-to-head fashion leading to BRET from Rluc to Qd upon addition of a substrate coelenterazine. The sensing system could detect target nucleic acid in buffer as well as in Escherichia coli cellular matrix in 5 min with a detection limit of 0.54 pmol. The ability to detect target nucleic acid rapidly in a cellular matrix with high sensitivity will prove highly beneficial in biomedical and environmental applications.

Optical properties and luminescence dynamics ofEu3 + -doped terbium orthophosphate nanophosphors

The development of luminescent inorganic nanocrystals (NCs) doped withrare-earth (RE) ions has attracted increasing interest owing to their distinctoptical properties and versatile applications in time-resolved bioassays,multiplex biodetection, DNA hybridization and bioimaging. HexagonalTbPO4:Eu3 + NCs (10–30 nm) were synthesized via a facile hydrothermal method assisted with oleic acid (OA)surfactants, which exhibit tunable emissions from green to red by varying the concentration ofEu3 + . TheTb3 + -to-Eu3 + energy transfer efficiency observed reaches up to 94%. Different from theirbulk counterparts, a new interface-state band (316 nm) in addition to thecommonly observed spin-forbidden 4f–5d transition band (265 nm) ofTb3 + wasfound to be dominant in the excitation spectrum of NCs due presumably to the formation of surfaceTbPO4/OA complexes,which provides an additional excitation antenna in practical utilization. Two kinds of luminescence sitesof Eu3 + inTbPO4 NCs, with the sitesymmetry of C2 or C1, were identified based on the emission spectra at 10 K and roomtemperature. Furthermore, the photoluminescence (PL) dynamics ofTb3 + ions inpure TbPO4 NCs have been revealed. Compared to the exponential PL decay in bulk counterpartsinduced by very fast energy migration, the non-exponential decay from 5D4 ofTb3 + inTbPO4 NCsis mainly attributed to the diffusion-limited energy migration due to more rapid energy transfer fromTb3 + to defects than theenergy migration among Tb3 + .

Thermal Decay and Reversal of Exchange Bias Field of CoFe/PtMn Bilayer after Ga+ Irradiation

An applied field is used to perform Ga+ ion irradiation on a CoFe/PtMn bilayer. Effects of the applied field and energy transfer between Ga+ ions and antiferromagnetic (AFM) atoms on the exchange bias field Hex are investigated. A partially reversed Hex is found in CoFe/PtMn specimens irradiated at a dose of 1 × 1014 ions/cm2 with an applied field anti-parallel to the original exchange bias direction. We believe that the rapid energy transfer and local temperature increase originating from the interaction between Ga+ ions and AFM atoms result in spin reversal and the formation of reversed AFM domains when specimens are irradiated with anti-parallel fields. The decrease in Hex when annealing the film in a negative saturation field indicates a thermal decay process. The AFM moments are reversed by thermal activation over an energy barrier distribution, which may change in some way as the temperature increases.

Dynamics of relaxation and fragmentation in size-selected icosahedral Arn[NO−(v = 1)] clusters

We study the vibrational relaxation and solvation dynamics in size-selected icosahedral Ar(n)(NO(-)) at 300 K, where NO(-)(X(3)Σ(-)) is in v = 1 and n = 1-12, using a classical dynamics method and an interaction model consisting of detailed host-guest and host-host interactions. Two relaxation time scales are found: (i) the short-time (<200 ps), in which rate is nearly independent of cluster size, and (ii) the ns scale, in which a slow energy transfer process occurs between NO(-) vibration and argon modes at a rate (~10(8) s(-1)) decreasing slightly from n = 12 to 6 and rapidly from n = 5 to 1 (~10(6) s(-1)). In Ar(12)(NO(-)), less than one-quarter of the host atoms sampled evaporate, nearly 60% of evaporation occurring within 200 ps caused by rapid energy transfer from NO(-) at short time. The fraction of evaporation decreases nearly exponentially with increasing evaporation time, but ~16% of evaporation still occurs on a time scale longer than 1 ns. Evaporation from one hemisphere of Ar(12)(NO(-)) dominates the rest. Final cluster sizes commonly produced from the fragmentation of Ar(12)(NO(-)) are n = 6-11 (evaporation of 6-1 atoms) and n = 12 (no evaporation).