Fast Energy Transfer Research Articles

Coupling-dependent rate of energy transfer from photoexcited Mott insulators to lattice vibrations

Photoexcited states are relaxed by transferring energy to the environments. In order to study which coupling allows fast energy transfer to lattice vibrations in correlated electron systems, we calculate the time evolutions of the kinetic energies of different types and frequencies of lattice vibrations. The one-dimensional half-filled Hubbard model is augmented with electron-lattice couplings that modulate transfer integrals, site energies, and Coulomb repulsion strengths. The time-dependent Schr\odinger equation is solved for exact many-electron wave functions, and the classical equation of motion for the lattice displacements. In order to transfer energy to classical lattice vibrations that modulate transfer integrals or site energies, the translational invariance must be broken to give optical activity to an electronic excitation with wave number $\ensuremath{\pi}$ and to these lattice vibrations. On the other hand, a certain amount of energy is always transferred to lattice vibrations that modulate Coulomb repulsion strengths, irrespective of the symmetry of the ground state, as long as the corresponding electron-lattice couplings are present. In strongly correlated electron systems, these couplings can be strong, although they are usually insignificant because their effects on the equilibrium properties can be absorbed into redefinition of Coulomb repulsion strengths. We will discuss competition or collaboration between energy-transfer pathways through different types of electron-lattice couplings.

Femtosecond Carotenoid to Retinal Energy Transfer in Xanthorhodopsin

Xanthorhodopsin of the extremely halophilic bacterium Salinibacter ruber represents a novel antenna system. It consists of a carbonyl carotenoid, salinixanthin, bound to a retinal protein that serves as a light-driven transmembrane proton pump similar to bacteriorhodopsin of archaea. Here we apply the femtosecond transient absorption technique to reveal the excited-state dynamics of salinixanthin both in solution and in xanthorhodopsin. The results not only disclose extremely fast energy transfer rates and pathways, they also reveal effects of the binding site on the excited-state properties of the carotenoid. We compared the excited-state dynamics of salinixanthin in xanthorhodopsin and in NaBH 4-treated xanthorhodopsin. The NaBH 4 treatment prevents energy transfer without perturbing the carotenoid binding site, and allows observation of changes in salinixanthin excited-state dynamics related to specific binding. The S 1 lifetimes of salinixanthin in untreated and NaBH 4-treated xanthorhodopsin were identical (3 ps), confirming the absence of the S 1-mediated energy transfer. The kinetics of salinixanthin S 2 decay probed in the near-infrared region demonstrated a change of the S 2 lifetime from 66 fs in untreated xanthorhodopsin to 110 fs in the NaBH 4-treated protein. This corresponds to a salinixanthin-retinal energy transfer time of 165 fs and an efficiency of 40%. In addition, binding of salinixanthin to xanthorhodopsin increases the population of the S ∗ state that decays in 6 ps predominantly to the ground state, but a small fraction (<10%) of the S ∗ state generates a triplet state.

Lutein Can Act as a Switchable Charge Transfer Quencher in the CP26 Light-harvesting Complex

Energy-dependent quenching of excitons in photosystem II of plants, or qE, has been positively correlated with the transient production of carotenoid radical cation species. Zeaxanthin was shown to be the donor species in the CP29 antenna complex. We report transient absorbance analyses of CP24 and CP26 complexes that bind lutein and zeaxanthin in the L1 and L2 domains, respectively. For CP24 complexes, the transient absorbance difference profiles give a reconstructed transient absorbance spectrum with a single peak centered at approximately 980 nm, consistent with zeaxanthin radical cation formation. In contrast, CP26 gives constants for the decay components probed at 940 and 980 nm of 144 and 194 ps, a transient absorbance spectrum that has a main peak at 980 nm, and a substantial shoulder at 940 nm. This suggests the presence of two charge transfer quenching sites in CP26 involving zeaxanthin radical cation and lutein radical cation species. We also show that lutein radical cation formation in CP26 is dependent on binding of zeaxanthin to the L2 domain, implying that zeaxanthin acts as an allosteric effector of charge transfer quenching involving lutein in the L1 domain.

White light generation by resonant nonradiative energy transfer from epitaxial InGaN/GaN quantum wells to colloidal CdSe/ZnS core/shell quantum dots

We propose and demonstrate white-light-generating nonradiative energy transfer (ET) from epitaxial quantum wells (QWs) to colloidal quantum dots (QDs) in their close proximity. This proof-of-concept hybrid color-converting system consists of chemically synthesized red-emitting CdSe/ZnS core/shell heteronanocrystals intimately integrated on epitaxially grown cyan-emitting InGaN/GaN QWs. The white light is generated by the collective luminescence of QWs and QDs, for which the dot emission is further increased by 63% with nonradiative ET, setting the operating point in the white region of CIE chromaticity diagram. Using cyan emission at 490 nm from the QWs and red emission at 650 nm from the nanocrystal (NC) luminophors, we obtain warm white light generation with a correlated color temperature of Tc = 3135 K and tristimulus coordinates of (x,y) = (0.42, 0.39) in the white region. By analyzing the time-resolved radiative decay of these NC emitters in our hybrid system with a 16 ps time resolution, the luminescence kinetics reveals a fast ET with a rate of (2 ns)-1 using a multiexponential fit with χ 2 = 1.0171.

Ultrafast Carrier Relaxation in InN Nanowires Grown by Reactive Vapor Transport

We have studied femtosecond carrier dynamics in InN nanowires grown by reactive vapor transport. Transient differential absorption measurements have been employed to investigate the relaxation dynamics of photogenerated carriers near and above the optical absorption edge of InN NWs where an interplay of state filling, photoinduced absorption, and band-gap renormalization have been observed. The interface between states filled by free carriers intrinsic to the InN NWs and empty states has been determined to be at 1.35 eV using CW optical transmission measurements. Transient absorption measurements determined the absorption edge at higher energy due to the additional injected photogenerated carriers following femtosecond pulse excitation. The non-degenerate white light pump-probe measurements revealed that relaxation of the photogenerated carriers occurs on a single picosecond timescale which appears to be carrier density dependent. This fast relaxation is attributed to the capture of the photogenerated carriers by defect/surface related states. Furthermore, intensity dependent measurements revealed fast energy transfer from the hot photogenerated carriers to the lattice with the onset of increased temperature occurring at approximately 2 ps after pulse excitation.

Exploring the Effects of Intramolecular Vibrational Energy Redistribution on the Operation of the Proton Wire in Green Fluorescent Protein

The operation of the proton wire in Green Fluorescent Protein has been simulated by quantum dynamics and considering the coupling to the protein environment by means of a bath of harmonic oscillators. The simulation consists of 36 explicit and fully quantum degrees of freedom: 6 degrees of freedom represent the configuration of the proton wire, which are coupled to 30 bath coordinates. Regimes of weak and strong coupling have been studied. It is found that presence of the bath induces a fast energy transfer from the proton wire to the bath, with characteristic times under 400 fs. This internal vibrational redistribution happens at the expense of the potential energy content of the proton wire, deformed through the interaction to the bath from its uncoupled state. Strong coupling induces a slowing-down of the operation of the wire because it hinders to some extent the approaching of donor and acceptor atoms to distances in which proton transfer can occur. Internal vibrational energy redistribution affects the dynamics, but from our simulations we conclude that it cannot be the only cause responsible for the experimentally reported fluorescence rise times.

Optoelectronic and Charge Transport Properties at Organic−Organic Semiconductor Interfaces: Comparison between Polyfluorene-Based Polymer Blend and Copolymer

We report detailed studies of optoelectronic and charge transport properties at the organic-organic semiconductor interfaces formed between polymer chains (interchain) and within a polymer chain (intrachain). These interfaces are fabricated using poly(9,9-di-n-octylfluorene-alt-N-(4-butylphenyl)diphenylamine) (TFB [f8-tfb]) (electron-donor) and poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT [f8-bt]) (electron-acceptor) conjugated polymers, by blending them together or by covalently attaching them via a main polymer backbone (copolymer). For optoelectronic properties, when a bulky and twisted tfb molecule is incorporated into a rigid F8BT conjugated backbone, it disturbs the conjugation of F8BT polymer, leading to a blue-shift in the lowest absorption transition. However, by acting as an effective electron donor, it assists the formation of an intrachain singlet exciton that has a strong charge-transfer character, leading to a red-shifted and longer-lived emission than that of F8BT. An extremely efficient and fast energy transfer from tfb donor to bt acceptor is observed in the copolymer (<1 ps) compared to transfer from TFB to F8BT in the blend (tens of ps). This efficient energy transfer in the copolymer is found to be associated with its low fluorescence efficiency (40-45% vs 60-65% for blend) because of the migration of radiative singlet excitons to low-energy states such as triplet and exciplex states that are nonemissive or weakly emissive. The presence of molecular-scale tfb-f8-bt interfaces in the copolymer, however, does not hinder an efficient transport of charge carriers at high drive voltages. Instead, it provides a better balance of charge carriers inside the device, which leads to slower decay of the device efficiency and thus more stable light-emitting diodes with increasing voltage than the blend devices. These distinctive optoelectronic and charge transport properties observed at different organic-organic semiconductor interfaces will provide useful input for the design rules of conjugated polymers required for improved molecular electronics.

Sensitivity of ion-induced sputtering to the radial distribution of energy transfers: A molecular dynamics study

Using different models for the deposition of energy on the lattice and a classical molecular dynamics approach to the subsequent transport, we evaluate how the details of the energy deposition model influence sputtering yield from a Lennard-Jones target irradiated with a MeV/u ion beam. Two energy deposition models are considered: a uniform, instantaneous deposition into a cylinder of fixed radius around the projectile ion track, used in earlier molecular dynamics and fluid dynamics simulations of sputtering yields; and an energy deposition distributed in time and space based on the formalism developed in the thermal spike model. The dependence of the sputtering yield on the total energy deposited on the target atoms is very sensitive to the energy deposition model. To clarify the origin of this strong dependence, we explore the role of the radial expansion of the electronic system prior to the transfer of its energy to the lattice. The results imply that observables such as the sputtering yield may be used as signatures of the fast electron-lattice energy transfer in the electronic energy-loss regime, and indicate the need for more experimental and theoretical investigations of these processes.

How Close Can You Get? Studies of Ultrafast Light-Induced Processes in Ruthenium-[60] Fullerene Dyads with Short Pyrazolino and Pyrrolidino Links

Two pyrazoline- and one pyrrolidine-bridged Ru(II)bipyridine-[60]fullerene dyads have been prepared and studied by ultrafast time-resolved spectroscopy. A silver-assisted synthesis route, in which Ag(I) removes the chlorides from the precursor complex Ru(bpy) 2Cl 2 facilitates successful coordination of the [60]fullerene-substituted third ligand. Upon light excitation of the ruthenium moiety, the emission was strongly quenched by the fullerene. The main quenching mechanism is an exceptionally fast direct energy transfer ( k obs > 1 x 10 (12) s (-1) in the pyrazoline-bridged dyads), resulting in population of the lowest excited triplet state of fullerene. No evidence for electron transfer was found, despite the extraordinarily short donor-acceptor distance that could kinetically favor that process. The observations have implications on the ongoing development of devices built from Ru-polypyridyl complexes and nanostructured carbon, such as C 60 or nanotubes.

Triplet Pathways in Diarylethene Photochromism: Photophysical and Computational Study of Dyads Containing Ruthenium(II) Polypyridine and 1,2-Bis(2-methylbenzothiophene-3-yl)maleimide Units

A 1,2-bis(2-methylbenzothiophene-3-yl)maleimide model ( DAE) and two dyads in which this photochromic unit is coupled, via a direct nitrogen-carbon bond ( Ru-DAE) or through an intervening methylene group ( Ru-CH 2-DAE ), to a ruthenium polypyridine chromophore have been synthesized. The photochemistry and photophysics of these systems have been thoroughly characterized in acetonitrile by a combination of stationary and time-resolved (nano- and femtosecond) spectroscopic methods. The diarylethene model DAE undergoes photocyclization by excitation at 448 nm, with 35% photoconversion at stationary state. The quantum yield increases from 0.22 to 0.33 upon deaeration. Photochemical cycloreversion (quantum yield, 0.51) can be carried out to completion upon excitation at lambda > 500 nm. Photocyclization takes place both from the excited singlet state (S 1), as an ultrafast (ca. 0.5 ps) process, and from the triplet state (T 1) in the microsecond time scale. In Ru-DAE and Ru-CH 2-DAE dyads, efficient photocyclization following light absorption by the ruthenium chromophore occurs with oxygen-sensitive quantum yield (0.44 and 0.22, in deaerated and aerated solution, respectively). The photoconversion efficiency is almost unitary (90%), much higher than for the photochromic DAE alone. Efficient quenching of both Ru-based MLCT phosphorescence and DAE fluorescence is observed. A complete kinetic characterization has been obtained by ps-ns time-resolved spectroscopy. Besides prompt photocyclization (0.5 ps), fast singlet energy transfer takes place from the excited diarylethene to the Ru(II) chromophore (30 ps in Ru-DAE, 150 ps in Ru-CH 2-DAE ). In the Ru(II) chromophore, prompt intersystem crossing to the MLCT triplet state is followed by triplet energy transfer to the diarylethene (1.5 ns in Ru-DAE, 40 ns in Ru-CH 2-DAE ). The triplet state of the diarylethene moiety undergoes cyclization in a microsecond time scale. The experimental results are complemented with a combined ab initio and DFT computational study whereby the potential energy surfaces (PES) for ground state (S 0) and lowest triplet state (T 1) of the diarylethene are investigated along the reaction coordinate for photocyclization/cycloreversion. At the DFT level of theory, the transition-state structures on S 0 and T 1 are similar and lean, along the reaction coordinate, toward the closed-ring form. At the transition-state geometry, the S 0 and T 1 PES are almost degenerate. Whereas on S 0 a large barrier (ca. 45 kcal mol (-1)) separates the open- and closed-ring minima, on T 1 the barriers to isomerization are modest, cyclization barrier (ca. 8 kcal mol (-1)) being smaller than cycloreversion barrier (ca. 14 kcal mol (-1)). These features account for the efficient sensitized photocyclization and inefficient sensitized cycloreversion observed with Ru-DAE. Triplet cyclization is viewed as a nonadiabatic process originating on T 1 at open-ring geometry, proceeding via intersystem crossing at transition-state geometry, and completing on S 0 at closed-ring geometry. A computational study of the prototypical model 1,2-bis(3-thienyl)ethene is used to benchmark DFT results against ab initio CASSCF//CASPT2 results and to demonstrate the generality of the main topological features of the S 0 and T 1 PES obtained for DAE. Altogether, the results provide strong experimental evidence and theoretical rationale for the triplet pathway in the photocyclization of photochromic diarylethenes.

Analysis of the CH-chromophore spectra and dynamics in dideutero-methyliodide CHD2I1

We report the infrared spectra of dideutero-methyliodide CHD2I in the range from 500 to 12 000 cm−1. Twenty two vibrational bands were assigned to the coupled CH-stretching and bending vibrations of the CH-chromophore. They were analysed in terms of an effective Hamiltonian including strong anharmonic resonances up to the polyad N = 4 corresponding to a maximum of four quanta of stretching excitation. The ab initio potential hypersurface for the three-dimensional CH-chromophore subspace was calculated at the full MP2 level. This surface was finally scaled to fit experiment with vibrational energy levels being calculated by an adiabatic successive truncation technique. The resulting spectrum was represented by the same effective Hamiltonian as used for the experimental data, the results from both approaches agreeing well. The time-dependent quantum dynamics were obtained from this Hamiltonian adjusted to experiment. It showed very fast but incomplete energy transfer from pure CH-stretching excitation with four or five quanta to partial CH-bending excitation in about 100 fs. These results are discussed in terms of a doorway to further excitation transfer to the lower frequency modes measured before by femtosecond pump–probe experiments in our group. 1Dedicated to Hubert van den Bergh on the occasion of his 65th birthday.

DNA hybridization detection in a microfluidic channel using two fluorescently labelled nucleic acid probes

A conceptually new technique for fast DNA detection has been developed. Here, we report a fast and sensitive online fluorescence resonance energy transfer (FRET) detection technique for label-free target DNA. This method is based on changes in the FRET signal resulting from the sequence-specific hybridization between two fluorescently labelled nucleic acid probes and target DNA in a PDMS microfluidic channel. Confocal laser-induced microscopy has been used for the detection of fluorescence signal changes. In the present study, DNA hybridizations could be detected without PCR amplification because the sensitivity of confocal laser-induced fluorescence detection is very high. Two probe DNA oligomers (5′-CTGAT TAGAG AGAGAA-TAMRA-3′ and 5′-TET-ATGTC TGAGC TGCAGG-3′) and target DNA (3′-GACTA ATCTC TCTCT TACAG GCACT ACAGA CTCGA CGTCC-5′) were introduced into the channel by a microsyringe pump, and they were efficiently mixed by passing through the alligator teeth-shaped PDMS microfluidic channel. Here, the nucleic acid probes were terminally labelled with the fluorescent dyes, tetrafluororescein (TET) and tetramethyl-6-carboxyrhodamine (TAMRA), respectively. According to our confocal fluorescence measurements, the limit of detection of the target DNA is estimated to be 1.0 × 10 −6 to 1.0 × 10 −7 M. Our result demonstrates that this analytical technique is a promising diagnostic tool that can be applied to the real-time analysis of DNA targets in the solution phase.

Photosystem I complexes associated with fucoxanthin-chlorophyll-binding proteins from a marine centric diatom, Chaetoceros gracilis

Diatoms occupy a key position as a primary producer in the global aquatic ecosystem. We developed methods to isolate highly intact thylakoid membranes and the photosystem I (PS I) complex from a marine centric diatom, Chaetoceros gracilis. The PS I reaction center (RC) was purified as a super complex with light-harvesting fucoxanthin-chlorophyll (Chl)-binding proteins (FCP). The super complex contained 224 Chl a, 22 Chl c, and 55 fucoxanthin molecules per RC. The apparent molecular mass of the purified FCP–PS I super complex (∼ 1000 kDa) indicated that the super complex was composed of a monomer of the PS I RC complex and about 25 copies of FCP. The complex contained menaquinone-4 as the secondary electron acceptor A 1 instead of phylloquinone. Time-resolved fluorescence emission spectra at 77 K indicated that fast (16 ps) energy transfer from a Chl a band at 685 nm on FCP to Chls on the PS I RC complex occurs. The ratio of fucoxanthin to Chl a on the PS I-bound FCP was lower than that of weakly bound FCP, suggesting that PS I-bound FCP specifically functions as the mediator of energy transfer between weakly bound FCPs and the PS I RC.

Fast energy transfer within a self-assembled cyclic porphyrin tetramer

The structure of a cyclic self-assembled tetramer of an asymmetric meso-ethynylpyridyl-functionalized Zn(II)-porphyrin was established by solution-phase X-ray scattering and diffraction; femtosecond transient absorption and anisotropy spectroscopies were used to (a) observe rapid energy transfer (3.8 ps(-1)) between porphyrin subunits and (b) establish that the transfer occurs between adjacent units.

Femtosecond depolarization dynamics of tris(8-hydroxyquinoline) aluminum films

For vapor-deposited tris(8-hydroxyquinoline) aluminum thin films, steady-state and subpicosecond transient optical anisotropy are investigated. It is found that the transient absorption anisotropy decays within tens of picoseconds. With a simple model calculation, the excited state population and anisotropy decay dynamics are disentangled, and the latter signal, the depolarization of the excited state, is explained by the energy transfer between the non-orthogonally-coordinated quinolate ligands. It is also shown that there are two pathways for this fast interligand energy transfer.

Equilibration between Three Different Excited States in a Bichromophoric Copper(I) Polypyridine Complex

Fast reversible energy transfer and intersystem crossing conspire to permit excited-state equilibration between three excited states in a copper(I) phenanthroline complex. Introduction of multiple quasi-isoenergetic excited states in a planned fashion represents a new strategy to prolong luminescence lifetimes of copper phenanthroline complexes (e.g., 1.2 μs compared with 70 ns for the parent complex).

Hindered Coulomb explosion of embedded Na clusters — stopping, shape dynamics and energy transport

We investigate the dynamical evolution of a Na8 cluster embedded in Ar matrices of various sizes from N=30 to 1048. The system is excited by an intense short laser pulse leading to high ionization stages.We analyze the subsequent highly non-linear motion of cluster and Ar environment in terms of trajectories, shapes, and energy flow. The most prominent effects are: temporary stabilization of high charge states for several ps, sudden stopping of the Coulomb explosion of the embedded Na8 clusters associated with an extremely fast energy transfer to the Ar matrix, fast distribution of energy throughout the Ar layers by a sound wave. Other ionic-atomic transfer and relaxation processes proceed at slower scale of few ps. The electron cloud is almost thermally decoupled from ions and thermalizes far beyond the ps scale.

Inter- and intra-molecular energy transfer during sensitization of Eu(DBM) 3Phen luminescence by Tb(DBM) 3Phen in PMMA

A series of Eu(DBM) 3Phen and Tb(DBM) 3Phen co-doped poly(methyl methacrylate) (Eu x Tb y -PMMA, subscript x and y denote molar ratio of the ion to repeating unit of PMMA in each sample) were prepared with different Eu/Tb contents. During luminescence measurement of these samples, it was found that for Eu 0.010Tb 0-PMMA the maximum excitation was found to be at 363 nm, and for Eu 0Tb 0.010-PMMA the maximum excitation at 274 nm. This difference reveals that there is different intra-molecular energy transfer mechanism for these two complexes, which contain the same ligands but different central ions. For Eu 0.0050Tb y -PMMA ( y = 0, 5.0 × 10 −6, 3.0 × 10 −5, 5.0 × 10 −5, 3.0 × 10 −4, 4.0 × 10 −4, 1.0 × 10 −3, 4.0 × 10 −3, 1.0 × 10 −2, 2.0 × 10 −2, 4.0 × 10 −2, 6.0 × 10 −2 and 8.0 × 10 −2, respectively), enhanced luminescence of Eu 3+ at 612 nm for 5D 0 → 7F 2 was observed at the concentration of Tb 3+ higher than 0.0048 mol/L. At this Tb 3+ content, the minimum intensity of the luminescence of Eu(DBM) 3Phen was observed, which comes from the balance between absorption consumption of ligands in Tb(DBM) 3Phen and sensitizing in luminescence of Eu 3+ by Tb 3+. Eu x Tb 0.010-PMMA ( x = 0, 5.0 × 10 −3, 8.0 × 10 −3, 9.0 × 10 −3, 0.013, 0.020, 0.030, 0.040 and 0.060) showed a gradually increasing emission of Eu 3+ at 535 nm along with decreasing of Tb 3+ emission at 546 nm, which resulted from a fast intra-molecular energy transfer from 5D 1 to 5D 0 of Eu 3+ and an inter-molecular energy transfer from the triplet state of DBM in Tb(DBM) 3Phen to 5D 1 of Eu 3+, and the latter energy transfer process is directly dependent on the distance between two kinds of ions. Based on observation above, it was realized that there will be a critical distance between two kinds of complexes in each Eu xTb y-PMMA sample, which determines the minimum concentration of Tb(DBM) 3Phen for the sensitization in luminescence of the sample. To give a vivid picture for this complex system, a model for the sensitization of Eu xTb y-PMMA was established in terms of Perrin formulation. The radius of the quenching sphere, which corresponds to the critical distance between Eu 3+ and Tb 3+, was found to be 1.633 nm for the sensitization in Eu xTb y-PMMA.

On the energy transfer between quasi-degenerate states with uncorrelated site distribution functions: An application to the CP43 complex of Photosystem II

The possible influence of excitation energy transfer on various spectra observable in hole burning (HB) experiments has been analyzed for pigments with quasi-degenerate absorption bands with uncorrelated site distribution functions. It was shown that ignoring this influence can lead to incorrect interpretation of experimental results. Application of the model is demonstrated for the CP43 core antenna complex of plant Photosystem II, which possesses two quasi-degenerate lowest-energy states [Jankowiak et al., J. Phys. Chem. B 104 (2000) 11805]. According to the model, bands A and B observed in HB experiments do not truly represent the whole absorption bands of the two lowest-energy states in CP43. Assuming that the sample can be represented as a sum of the sub-ensembles of the CP43 complexes where one or another state is the lowest-energy one (and therefore is incapable of downhill energy transfer), bands A and B are the lowest-energy bands of these sub-ensembles. With this restriction, the model allows for fast energy transfer between the two lowest-energy chromophores (states) in CP43. It is shown that the transient and persistent HB spectra of the isolated CP43 complexes are in good agreement with the model.

Convenient Synthesis of Green Diisoindolodithienylpyrromethene−Dialkynyl Borane Dyes

[structure: see text] Versatile dyes based on diisoindolodithienylpyrromethene substituted at the boron center by alkynylaryl chromophores have been developed that efficiently fluorescence in the near infrared. Fast intramolecular energy transfer from the appended alkynyl units to the central core provides Stokes shifts above 16,000 cm(-1).