Complete Energy Transfer Research Articles

Quantum-state resolved reaction dynamics at the gas-liquid interface: Direct absorption detection of HF(v,J) product from F(P2)+Squalane

Exothermic reactive scattering of F atoms at the gas-liquid interface of a liquid hydrocarbon (squalane) surface has been studied under single collision conditions by shot noise limited high-resolution infrared absorption on the nascent HF(v,J) product. The nascent HF(v,J) vibrational distributions are inverted, indicating insufficient time for complete vibrational energy transfer into the surface liquid. The HF(v=2,J) rotational distributions are well fit with a two temperature Boltzmann analysis, with a near room temperature component (T(TD) approximately equal to 290 K) and a second much hotter scattering component (T(HDS) approximately equal to 1040 K). These data provide quantum state level support for microscopic branching in the atom abstraction dynamics corresponding to escape of nascent HF from the liquid surface on time scales both slow and fast with respect to rotational relaxation.

π‐Conjugated Chelating Polymers with Charged Iridium Complexes in the Backbones: Synthesis, Characterization, Energy Transfer, and Electrochemical Properties

A series of pi-conjugated chelating polymers with charged iridium (Ir) complexes in the backbones were synthesized by a Suzuki polycondensation reaction, leading to homogeneous polymeric materials that phosphoresce red light. The fluorene and bipyridine (bpy) segments were used as polymer backbones. 5,5'-Dibromobipyridine served as a ligand to form a charged iridium complex monomer with 1-(9'9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligand. Chemical and photophysical characterization confirmed that Ir complexes were incorporated into the backbones as one of the repeat units by means of the 5,5'-dibromobipyridine ligand. Chelating polymers showed almost complete energy transfer from the host fluorene segments to the guest Ir complexes in the solid state when the feed ratio was 2 mol %. In the films of the corresponding blend system, however, energy transfer was not complete even when the content of Ir complexes was as high as 16 mol %. Both intra- and intermolecular energy-transfer processes existed in this host-guest system, and the intramolecular energy transfer was a more efficient process. All chelating polymers displayed good thermal stability, redox reversibility, and film formation. These chelating polymers also showed more efficient energy transfer than the corresponding blended system and the mechanism of incorporation of the charged Ir complexes into the pi-conjugated polymer backbones efficiently avoided the intrinsic problems associated with the blend system, thus offering promise in optoelectronic applications.

Self-assembling and light-harvesting properties of fluorescent linear condensed aromatic gelators

Abstract The self-assembling and photophysical properties of soluble fluorescent linear condensed aromatic gelators are reported. The gels formed by 2,3-alkoxy derivatives are constituted of nanofibers weaving a 3-dimensional supramolecular network and imprisoning the solvent. These nanofibers are efficient light-harvesting systems in which complete energy transfer toward a fluorescent acceptor can be achieved at doping levels below 1 mol % of acceptor.

Modulating phase-separation in blends of MEHPPV- x with different conjugation lengths

We report here the phase-separation and energy transfer characteristics of segmented MEHPPV blends with two different distributions of conjugation lengths, namely MEHPPV-8 (LC, low conjugation length) and MEHPPV-100 (HC, high conjugation length). Thin films containing varying weight fractions of LC and HC were spin-cast from chloroform solutions. Photoluminescence studies of these thin films suggested that complete energy transfer from LC to HC occurred even though there was phase-separation. Selective chain-collapse of MEHPPV-100 by using a solution containing increasing volume fraction of cyclohexane for spin-coating allowed one to modulate the extent of energy transfer to some extent—typically the extent of energy transfer decreased in the presence of high volume fraction of cyclohexane.

Efficient Light Harvesting and Energy Transfer in Organic−Inorganic Hybrid Multichromophoric Materials

Thin films of silica hybrid materials consisting of two to three covalently bound organic chromophores at different ratios were conveniently synthesized and fabricated. The photophysical properties of these materials have been studied. The fluorescence spectra reveal complete fluorescence resonance energy transfer (FRET) from donor to acceptor, and the light-harvesting ability of these hybrid materials increases with increasing the molar fraction of donor chromophore. In a three-chromophore system, the energy is transferred from 300 to 530 nm successfully. Time-resolved fluorescence experiments are employed to elucidate the average rates and efficiencies (84-97%) of energy transfer in these organic/inorganic hybrid systems. The hybrid materials have been shown to provide antenna effect to facilitate energy transfer and light harvesting.

Conjugated random and alternating 2,3,4,5-tetraphenylsilole-containing polyfluorenes: Synthesis, characterization, strong solution photoluminescence, and light-emitting diodes

A novel series of soluble conjugated random and alternating copolymers derived from 9,9-dioctylfluorene (FO) and 1,1-dimethyl-2,3,4,5-tetraphenylsilole (PSP) were synthesized by Suzuki coupling reactions. The feed ratios of FO to PSP were 95:5, 90:10, 85:15, 70:30, and 50:50. Chemical structures and optoelectronic properties of the copolymers were characterized by elemental analysis, NMR, UV absorption, cyclic voltammetry, photoluminescence (PL), and electroluminescence (EL). The elemental analyses of the copolymers indicated that FO and PSP contents in the copolymers were very close to that of the feed compositions. Unlike the weak PL emission of PSP small molecules in a solution, PFO-PSP solutions could emit strong lights with PL quantum yields between 13 and 30%, indicating that the incorporation of the PSP into the conjugated rigid main chain could greatly restrict the rotations of the phenyl groups of the PSP units even in a solution. Compared with the solution PL, complete PL excitation energy transfer from the PFO segments to the PSP units could be achieved by film PL at lower PSP content. The films of the copolymers exhibited high absolute PL quantum yields between 55 and 84%. EL devices with a configuration of ITO/PEDOT/PFO-PSP/Ba/Al demonstrated that the PSP units could serve as powerful exciton traps, giving exclusively pure green EL emissions. A maximum external quantum efficiency of 1.51% was achieved using the PFO-PSP15 as the emissive layer.

Localization of the N-terminal Domain in Light-harvesting Chlorophyll a/b Protein by EPR Measurements

The conformational distribution of the N-terminal domain of the major light-harvesting chlorophyll a/b protein (LHCIIb) has been characterized by electron-electron double resonance yielding distances between spin labels placed in various domains of the protein. Distance distributions involving residue 3 near the N terminus turned out to be bimodal, revealing that this domain, which is involved in regulatory functions such as balancing the energy flow through photosystems (PS) I and II, exists in at least two conformational states. Models of the conformational sub-ensembles were generated on the basis of experimental distance restraints from measurements on LHCIIb monomers and then checked for consistency with the experimental distance distribution between residues 3 in trimers. Only models where residue 3 is located above the core of the protein and extends into the aqueous phase on the stromal side fit the trimer data. In the other state, which consequently is populated only in monomers, the N-terminal domain extends sideways from the protein core. The two conformational states may correspond to two functional states of LHCIIb, namely trimeric LHCIIb associated with PSII in stacked thylakoid membranes and presumably monomeric LHCIIb associated with PSI in nonstacked thylakoids. The switch between these two is known to be triggered by phosphorylation of Thr-6. A similar phosphorylation-induced conformational change of the N-terminal domain has been observed by others in bovine annexin IV which, due to the conformational switch, also loses its membrane-aggregating property.

Targeted energy transfer by Fermi resonance

The earlier theory of targeted energy transfer (TET) [S. Aubry, G. Kopidakis, A.M. Morgante, G.P. Tsironis, Physica B 296 (2001) 222] between weakly coupled nonlinear oscillators (or discrete breathers) is extended to the case where the nonlinear oscillators are resonant by harmonics (Fermi resonance). Defining new detuning and coupling functions depending on the order of the resonance, it is shown that complete energy transfer may also occur by harmonics resonance under a condition similar to those of TET. This effect is called Fermi targeted energy transfer (or FTET). This theory of FTET is applied for the weakly coupled rotor-Morse oscillator system modelling selective chemical dissociation described in [A. Memboeuf, S. Aubry, preprint submitted to Physica D]. It is shown that chemical dissociation still occur by Fermi resonance at least up to resonance of order 5. Quantum FTET is also briefly discussed and shown to be related to the existence of a path of degenerate quantum states at the uncoupled limit.

Investigation of Spectral-Luminescent and Lasing Properties of Bifluorophoric Molecules. I. Bifluorophores of Linear Structure

Eight bifluorophoric (BF) molecules on the basis of paratherphenyl, stilbene, phenyl, biphenyl (donors) and coumarin 120 and phenylphtalimide (acceptors) connected by the bridging -CH2- were experimentally studied. It is shown that the absorption spectra of the BF are virtually additive to donor and acceptor fragments. The acceptor band alone is present in the fluorescence spectrum, which points to a complete nonradiative transfer of the electronic excitation energy. The spectra of induced BF emisson under flash-lamp and laser excitations are also examined.

Miscibility effect on the energy transfer induced luminescence enhancement of polyimide/PVK blends

Two series of polyimides exhibiting red light luminescence were synthesized. The energy transfer between poly( N-vinylcarbazole) (PVK) and polyimide enhances the red light luminescence of the polyimide. Meanwhile, the purplish blue light luminescence of the pure PVK polymer was not or hardly observed in the light luminescence spectra of the polyimide/PVK blend depending on the composition of the blend. There was more spectral overlap between the PL emission of PVK and the absorption of the pyromellitic dianhydride (PMDA)–2,7-diaminofluorene (DAF) polyimide than that of the PMDA–3.7-diamino-2.8-dimethyldibenzo-thiophene sulfone (DAS) polyimide. Therefore, the PMDA–DAF polyimide/PVK blends that showed complete energy transfer exhibited the emission spectrum mostly from the polyimide. Incorporating a modified silicone surfactant further showed remarkable enhancement of the red luminescence by improving the miscibility of the blends of PMDA–DAF polyimide with PVK.

Classical and quantum targeted energy transfer between nonlinear oscillators

Complete energy exchange between two weakly coupled classical Klein–Gordon anharmonic oscillators is investigated. According to the recently introduced theory of targeted energy transfer [Physica B 296 (2001) 222; Phys. Rev. Lett. 87 (2001) 165501], the condition for a specific amount of energy initially on the donor to be completely transferred to the acceptor is that the detuning function, defined as the variation of the oscillators energy during a transfer conserving the total action, is bounded by a certain function determined by the coupling. We show that, for given donor with given initial energy, the potential of the acceptor can be numerically tuned so that the detuning function becomes exactly zero. Then, complete energy transfer occurs in the limit of zero coupling. We also show that it is sufficient to fit the coefficient of the nonlinearity of the acceptor at lowest order for obtaining a small, although nonzero, detuning function. Then, total energy transfer can be obtained at coupling larger than a nonzero but small critical value. Quantum targeted energy transfer is also investigated in the discrete nonlinear Schrödinger dimer and in the Klein–Gordon dimer. In both cases, it is found that a quantum wave packet on the donor at the classical energy for targeted transfer is transferred to the acceptor, as in the classical case. The wave packet oscillates back and forth between donor and acceptor but loses its coherence after some number of oscillations which tends to be large when approaching the classical limit. In the Klein–Gordon dimer the energy transfer cannot be complete, since the zero point energy of the donor cannot be removed. Quantum targeted transfer appears to be related to the existence of a quantum pathway of almost degenerate eigenenergies the variation of which becomes the detuning function in the classical limit.

The area theorems for two-core nonlinear directional couplers

The area theorems, describing propagation of ultrashort pulses of resonant laser radiation in a two-core nonlinear directional coupler, are formulated for the first time. It is shown that such a system is characterized by a finite, bounded above set of areas of the stationary propagating pulses. We also predict quantization of the limit cycles and possible existence of the regime of periodic complete transfer of the radiation energy from one fiber to another.

Synthesis of New Europium Complexes and Their Application in Electroluminescent Devices

AbstractSeveral substituted phenanthrolines (L = pyrazino[2,3‐f][1,10]phenanthroline (PyPhen), 2‐methylpyrazino[2,3‐f][1,10]phenanthroline (MPP), dipyrido[3,2‐a:2′,3′‐c]phenazine (DPPz), 11‐methyldipyrido[3,2‐a:2′,3′‐c]phenazine (MDPz), 11,12‐dimethyldipyrido[3,2‐a:2′,3′‐c]phenazine (DDPz), and benzo[i]dipyrido[3,2‐a:2,3‐c]phenazine (BDPz)) were successfully prepared and europium complexes Eu(TTA)3L (Eu‐L) based on these ligands were synthesized from EuCl3, 2‐thenoyltrifluoroacetone (TTA) and L in good yields. Irradiation at the absorption band between 320–390 nm of all these europium complexes, except Eu‐BDPz, in solution or in the solid state leads to the emission of a sharp red band at ∼ 612 nm, a characteristic Eu3+ emission due to the transition 5D0 → 7F2. No emission from the ligands was found. The result indicates that complete energy transfer from the ligand to the center Eu3+ ion occurs for these europium complexes. In contrast, the photoluminescence spectrum of Eu‐BDPz exhibits a strong emission at around 550 nm from the coordinated BDPz ligand and a weak emission at 612 nm from the central europium ion. Incomplete energy transfer from the ligand to the central Eu3+ ion was observed for the first time. Several electroluminescent devices (A–I) using Eu‐PyPhen, Eu‐MPP, Eu‐DPPz, and Eu‐DDPz as dopant emitters with the device configuration: TPD or NPB (50 nm)/Eu:CBP (1.7–7 %, 30 nm)/BCP (20–30 nm)/Alq (25–35 nm) (where TPD: 4,4′‐bis[N‐(p‐tolyl)‐N‐phenylamino]biphenyl; NPB: 4,4′‐bis[1‐naphthylphenylamino]biphenyl; CBP: 4,4′‐N,N′‐dicarbazole biphenyl; BCP: 2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline; Alq: tris[8‐hydroxyquinoline]aluminum) were fabricated. Some of these devices emit saturated red light and are the only europium complex‐based devices that show a brightness of more than 1000 cd m–2.

A diaminomaleonitrile derivative as a new dopant for red-light-emitting electroluminescent device

We have synthesized a novel dye material of N,N′-bis[4-(N,N′-diphenylamino)-benzalidene] diaminomaleonitrile (BAP), as a dopant for red-light-emitting electroluminescent (EL) device. We fabricated several types of EL devices by doping BAP into tris(8-quinoline) aluminium (Alq3) as the light-emitting layer, and investigated their EL properties. BAP has symmetric conjugated structure and could give sharp and intense photoluminescence in the red region. When BAP was doped into Alq3, the device gave bright red EL with the maximum intensity of about 6700 cd m−2 together with the contribution of Alq3 emission. By introducing rubrene as an assist-dopant, the maximum EL intensity increased to 15 700 cd m−2 when the bias voltage was 14.5 V. However, complete energy transfer to BAP has not been achieved.

Characterization of light emitting devices based on a single-walled carbon nanotube–polymer composite

We have fabricated and characterized hole-only and double-layer-type devices based on a single-walled carbon nanotube (SWCNT)–polyvinylcarbazole (PVK) composite. Studies of luminescence and device characteristics demonstrate that as the fraction of SWCNTs in the PVK medium increases in the range of 0–1.0 wt.%, the hole mobility and device performance are significantly improved due to the efficient hole injection and transport through highly conductive nanotubes. The dye-doped composite devices reveal a complete energy transfer and higher external quantum efficiencies.

Some rules to improve the energy resolution in alpha liquid scintillation with beta rejection

Abstract Two common scintillating mixtures dedicated to alpha measurements by means of alpha liquid scintillation with pulse shape discrimination were tested: the di-isopropylnaphthalene — based and the toluene-based solvents containing the commercial cocktails Ultima Gold AB® and Alphaex®. We show the possibility to enhance the resolution up to 200% by using no-water miscible cocktails and by reducing the optical path. Under these conditions, the resolution of about 200 keV can be obtained either by the Tri CarbTM or by the PeralsTM spectrometers. The time responses, e.g., the time required for a complete energy transfer between the initial interaction alpha particle-solvent and the final fluorescence of the organic scintillator, have been compared. Both cocktails present similar behavior. According to the Förster theory, about 6-10 ns are required to complete the energy transfer. For both apparatus, the detection limits were determined for α emitters. The sensitivity of the Tri Carb was improved by 300% but remains 40% lower than that of Perals, due to a higher α/β discrimination and the use of vials with lower optical path.

Polymer electrophosphorescent device: comparison of phosphorescent dye doped and coordinated systems

Abstract We have synthesized a new polymer, (poly(Ir(ppy)2(2-(4-vinylphenyl)pyridine))-co-vinylcarbazole)) [Ir complex copolymer], containing both carbazole and iridium(III) complex as side groups and fabricated electrophosphorescent polymer light emitting devices. The 1MLCT transition of Ir complex copolymer is almost same position and absorption intensity of 8% Ir(ppy)3 doped PVK. At a lower molar concentration of the Ir complex copolymer, the polymer exhibited emission only from the carbazole units. However, with gradual increase in the concentration of the Ir complex copolymer, emission from the Ir complex became dominant. Present results indicated the energy transfer takes place by the intermolecular energy transfer not the intramolecular energy transfer. From the PL and EL of film state, the emission maximum was observed at 512 nm, due to the radiative decay from the 3MLCT state to the ground state, confirming almost a complete energy transfer from carbazole to Ir complex. The device showed 4.4% maximum external quantum efficiency and 5.0 lm/W power efficiency and peak luminance of 12,900 cd/m2.

Synthesis of new iridium complexes and their electrophosphorescent properties in polymer light-emitting diodes

Several new iridium complexes with p-substituted 2-phenylpyridine (R-PPy) ligands have been synthesized and characterized. The complexes were incorporated into phosphorescent polymer light-emitting devices using soluble poly[1,4-bis(6′-cyano-6′-methylheptyloxy)phenylene] (CNPPP) as the host and the resultant materials compared with Ir(PPy)3-doped devices. Green electrophosphorescence was observed, with peak emission at about 495 and 515 nm. Among the devices fabricated, highly efficient polymer light-emitting diodes were obtained with CNPPP doped with fac-tris[2-(4-tert-butylphenyl)pyridinato]iridium. An external quantum efficiency of 4.4% (photoluminescence/electroluminescence) and a luminous efficiency of 10 cd A−1 were obtained at 120 cd m−2. These values remain at 4.2% and 10 cd A−1, respectively, at 2500 cd m−2. The improvement is attributed to improved interaction between the guest and host, and to better and more complete energy transfer from the host singlet to the guest triplet state. These results demonstrate that efficient electrophosphorescence is not limited to small molecule organic light-emitting diodes, it can also be achieved in devices made with polymer hosts.

Equilibrium temperature of water–ice aerosols in the high-latitude summer mesosphere

Previous models of the equilibrium temperature and existence regions of mesospheric aerosols have shown significant radiative heating of the aerosols and, consequently, a substantially reduced existence region. We have developed an iterative model that extends this previous work by incorporating a complete collisional energy transfer algorithm, including the effects of vertical winds and particle fall velocity, that is appropriate for the free molecular flow conditions found in the mesosphere. We have also updated the ice refractive index used in the model and accounted for the dependence of the radiative heating and collisional cooling terms on particle temperature. Finally, a radiation model has been used to calculate the solar, terrestrial and atmospheric radiative inputs including the effects of multiple scattering and atmospheric absorption. As with the previous models, the particle temperature is calculated under steady-state conditions, assuming the background gas temperature remains constant and the aerosol does not change size, state or altitude. Under these conditions, the largest differences from previous models occur as a result of the updated ice index of refraction, particularly in the visible, which produces significantly less aerosol heating. These temperatures are combined with the observed properties of mesospheric aerosols to place limits on the water vapour mixing ratio, vertical-wind speeds, and maximum particle sizes. It is found that H 2O mixing ratios of 10 ppmv and vertical winds of order 0.02 m s −1 are consistent with observed particle distributions, and these lead to a radiative limit on the maximum particle radius of 250 nm .

Poly[2-(N-carbazolyl)-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]/tris (8-hydroxyquinoline) aluminum heterojunction electroluminescent devices produced by cluster beam deposition methods

We have fabricated and characterized double-layer-type electroluminescent devices with the structure of indium-tin-oxide-coated glass/poly[2-(N-carbazolyl)-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (CzEH-PPV)/tris(8-hydroxyquinoline) aluminum (Alq3)/Li:Al, in which CzEH-PPV was used as a hole transport medium, and neutral and ionized cluster beam deposition (NCBD and ICBD) methods were applied to deposit Alq3. The surface morphology observed by atomic force microscopy shows that NCBD and especially ICBD methods are more efficient in producing flat and smooth thin film surfaces in comparison to the conventional physical vapor deposition method. Studies of photoluminescence, electroluminescence (EL), and device characteristics demonstrate that the polymeric thin film is susceptible to ion radiation damage and the NCBD-based devices show better device performance, including lower threshold and turn-on voltages, improved EL intensity-voltage, current density-voltage, and external quantum efficiency (EQE)-current characteristics. In addition, the doping effect of the highly fluorescent dye molecule 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran into the Alq3 layer reveals a complete energy transfer, color-tuning capability and enhanced EQEs.