Quantum Yield Of Energy Transfer Research Articles

Energy transfer in supramolecular calix[4]arene—Perylene bisimide dye light harvesting building blocks: Resolving loss processes with simultaneous target analysis

By the application of simultaneous target analysis of multiple femtosecond transient absorption data sets we have identified two loss channels within multi-chromophoric light harvesting arrays. Perylene bisimide-calix[4]arene arrays composed of up to three different types of perylene bisimide (PBI) chromophores, orange (o), red (r), and green (g) PBIs (named after their colors as solids), have previously been studied by transient absorption spectroscopy (Hippius et al., J. Phys. Chem C 112:2476, 2008) and here we present a simultaneous target analysis of those data matrices. A covalent system containing the red chromophore (r) and calix[4]arene (c), the rc system, shows extensive spectral evolution that can be described with four excited states (r1*→r2*→r3*→r4*→ground state). In the Perylene Orange calix[4]arene system (oc), a radical pair (ocRP) can be formed by photoinduced electron transfer (Hippius et al., J. Phys. Chem C 111:13988, 2007). In a simultaneous target analysis of the multichromophoric systems ocr, rcocr and ocrco the properties of rc and oc are integrated, and excitation energy transfer (EET) from o* to r* occurs. In addition, we demonstrate that the final Species Associated Difference Spectrum (SADS) also contains o bleach features that indicate an excitonic interaction, for ocr, rcocr and ocrco. In a simultaneous target analysis of rcg and gcrcg the properties of rc are integrated, and next to EET to g* we can resolve the formation of a new rcgRP that is formed from r1* or r2*, and represents a loss of 7 and 12%, respectively. In a simultaneous target analysis of ocrcg the properties of ocr and rcg are integrated, arriving at a consistent picture with an energy transfer quantum yield of formation of the excited state of the green PBI (g*) of 80%.

Manipulating the upconversion luminescence of Yb3+/Er3+ doped nanoparticles by the sheet-shaped nanocavity

Rare-earth doped upconversion luminescence is important for display and imaging field due to its narrow band, multicolor, long lifetime and high stability. However, low quantum yield of upconversion energy transfer, weak excited states absorption and slow spontaneous radiation rates lead to weak upconversion luminescence, which may dramatically limit the practical application of upconversion nanoparticles. Here, we report a metal-sheet-shaped plasmonic nanocavity consisting of gold and silver micro-sheets. It is found that the upconversion processes (including quantum yield of energy transfer, excited states absorption and spontaneous radiation rates) were enhanced by strong local electromagnetic field of the plasmonic nanocavity when RE3+ nanoparticles were filled in the plasmonic nanocavity. The significant enhancement of the luminescence and clear directional radiation were observed under 980 nm laser excitation. By adjusting the nanogap distance of the plasmonic nanocavity, we achieved a 75-fold enhancement in 654 nm emission. Benefiting from the plasmonic nanocavity, the upconversion luminescence exhibited a directional emission, which indicates the plasmonic near-field excitation contributed to the luminescence enhancement. These findings provide a candidate for ring light source and bio-imaging application.

The fluorescence quantum yield parameter in Förster resonance energy transfer (FRET)—Meaning, misperception, and molecular design

The fluorescence quantum yield parameter in Förster resonance energy transfer (FRET) processes underpins vital phenomena ranging from light harvesting in photosynthesis to design of sensors for monitoring physiological processes. The criteria for choosing a donor for use in FRET processes include chemical features (solubility, bioconjugatability, synthetic accessibility, and stability) as well as photophysical properties pertaining to absorption (wavelength and molar absorption coefficient) and fluorescence (wavelength and fluorescence quantum yield). The value of the donor fluorescence quantum yield (Φf, or emphatically, Φf(D)) alone has sometimes been thought (erroneously) to place a ceiling on the possible quantum yield of energy transfer (Φtrans). A high value of the donor Φf, while attractive, is not at all essential; indeed, many valuable candidates for use as FRET donors have likely been excluded on the basis of this injudiciously applied filter. Such disregard is unwarranted. In this tutorial overview, the equations for FRET are reviewed along with pertinent core concepts in photophysics. An analogy using simple hydraulics provides a pedagogical tool for the non-aficionado to better understand photochemical kinetics. Ten examples are presented of donor–acceptor systems with donors that exhibit a range of Φf values (0.60, 0.59. 0.21, 0.17, 0.12, 0.118, 0.04, 0.018, 0.007, and 0.003; i.e., 60%–0.3%), yet for each corresponding donor–acceptor pair, the value of Φtrans is at least 0.70 and in some cases nearly 1.00 (i.e., 70%–100%). The systems encompass protein, synthetic inorganic, and synthetic organic architectures. The objectives of this illustrative review are to deepen understanding of FRET and to broaden molecular design considerations by enabling selection from among a far richer set of donors for use in FRET processes.

Excitation-energy transfer under strong laser drive

Strong molecule-light interaction enables the control of molecular structures and dynamical processes. A model with strong laser drive is proposed to greatly enhance the intermolecular distance of resonant energy transfer, where the molecules are strongly driven by an optical cavity. The optimal Rabi frequency and quantum yield of energy transfer are observed, resulting from the trade off between dipole-dipole interaction and molecule-cavity coupling. When the strong drive at certain Rabi frequency is applied, a larger spatial range of effective energy transfer and a slower decay rate with the distance compared to the F\"orster mechanism of resonant energy transfer are observed in our model. Our work sheds light on spectroscopic study of the cooperative energy transfer in molecular polaritons.

Triplet Energy Transfer from Polymethine Dimers in the Complexes with Cucurbit[8]urils

Effect of cucurbit[8]uril on the efficiency of triplet–triplet energy transfer between the donor dimer and the acceptor monomer or dimer has been studied. The efficiency depends on the rate constant of quenching of donor delayed fluorescence by the triplet energy acceptor, on the lifetime of the donor triplet state in the absence of a quencher, and on the acceptor concentration. Triplet–triplet energy transfer between the 3,3'-diethylthiacarbocyanine dimer (donor) and indodicarbocyanine (acceptor) occurs with a rate constant of 1.5 × 108 L mol–1 s–1 . Replacing the indodicarbocyanine monomer by the thiadicarbocyanine dimer decreases the energy transfer rate constant by a factor of 4.5. In the case of the 3,3'-dimethylthiacarbocyanine dimer as a donor, the quantum yield of energy transfer to the indodicarbocyanine monomer decreases fourfold.

Validity of Förster Theory for Vibrational Energy Transfer in Low-Dimensional Water.

Kinetics of vibrational Förster resonance energy transfer between the OH bonds of one-, two-, and three-dimensional liquid water is modeled by a Förster type of theory reflecting the excluded volume of intermolecular pairs of the bonds. When the size of excluded volume is comparable to so-called Förster radius of the bonds, the energy transfer kinetics is delayed from the prediction of Förster theory. The delay persists longer in the lower dimensions and results in the quantum yield of energy transfer to deviate more largely from the prediction of Förster theory. The excluded volume which is not taken into account by Förster theory is a critical factor for the correct description of vibrational Förster resonance energy transfer particularly in low-dimensional water.

Abstract LB-9: Light-controllable nano-drug delivery system with deep tissue penetrating ability for cancer therapy with two-photon-triggered nanoimpellers

Abstract Controllable drug delivery is urgently pursued for cancer therapy, because conventional chemotherapy is associated with serious toxic side effects. Precisely controlled external stimuli-activated nanoparticles are promising, as selective activation of the system takes place only upon stimulation of trigger signals and only in the area of interest. Silica nanoparticles have a number of advantages such as well established synthesis methods, chemical and thermal stability, large drug loading capacity, and the ease to carry out various surface modifications. We previously showed that our mesoporous silica nanoparticle-based nanoimpellers are effective for photo-activated drug delivery. However, like other light activating nanoparticles, our nanoimpeller also employed UV/Vis light, thus limiting its medical applications due to its short wavelength and inability for deep tissue penetration. Here we report our new generation of nanoimpellers functionalized with two-photon fluorophore that has a high two photon absorption cross-section, suitable for fluorescence resonance energy transfer (FRET) to photoisomerize azobenzene moieties in the NIR region. The azobenzene residing in the porous framework allows physical entrapment of the anticancer drug camptothecin, which is then propelled out of the pores by two-photon-triggered photoisomerization, resulting in on-demand intracellular drug release. Intracellular release of molecules is dependent on light excitation powers and wavelengths, and the anticancer drug delivery inside of cells can be regulated with light excitation. TPE fluorescence imaging was performed to demonstrate the cellular uptake of the nanoimpellers. Nanoimpeller with a high energy transfer quantum yield from the fluorophore to the azobenzene moiety was able to induce cancer cell death under these TPE conditions and did not show toxicity to control cells that were shielded from light. In a similar but different design, we also synthesized nanoparticles that have nanovalves placed at the pore openings. These results suggest that our newly synthesized two-photon-activated nanoimpellers could be useful for cancer therapy because of deep tissue penetrating ability and controllability. Actual application of such light-triggered delivery system in animal models remains to be proven, but we believe this two-photon light-activated mesoporous silica nanoparticles have a broad application prospects for biomedicine. Citation Format: Jie lu, Jonas Croissant, Jean-Olivier Jean-Olivier Durand, Tania Guardado-Alvarez, Jeffrey I. Zink, Fuyuhiko Tamanoi. Light-controllable nano-drug delivery system with deep tissue penetrating ability for cancer therapy with two-photon-triggered nanoimpellers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-9. doi:10.1158/1538-7445.AM2014-LB-9

Impact of local compressive stress on the optical transitions of single organic dye molecules

The ability to mechanically control the optical properties of individual molecules is a grand challenge in nanoscience and could enable the manipulation of chemical reactivity at the single-molecule level. In the past, light has been used to alter the emission wavelength of individual molecules or modulate the energy transfer quantum yield between them. Furthermore, tensile stress has been applied to study the force dependence of protein folding/unfolding and of the chemistry and photochemistry of single molecules, although in these mechanical experiments the strength of the weakest bond limits the amount of applicable force. Here, we show that compressive stress modifies the photophysical properties of individual dye molecules. We use an atomic force microscope tip to prod individual molecules adsorbed on a surface and follow the effect of the applied force on the electronic states of the molecule by fluorescence spectroscopy. Applying a localized compressive force on an isolated molecule induces a stress that is redistributed throughout the structure. Accordingly, we observe reversible spectral shifts and even shifts that persist after retracting the microscope tip, which we attribute to transitions to metastable states. Using quantum-mechanical calculations, we show that these photophysical changes can be associated with transitions among the different possible conformers of the adsorbed molecule.

A light-harvesting porphyrin-boron dipyrromethene conjugate

Click chemistry has been successfully applied to prepare a conjugate of zinc(II) porphyrin with four boron dipyrromethene moieties. Upon excitation at the latter, an efficient excitation energy transfer to the porphyrin core occurs with an energy transfer quantum yield of 0.98, making this conjugate a promising light-harvesting system.

Photoinduced intra-molecular energy transfer in a novel zinc (II) phthalocyanine bearing poly (aryl benzyl ether) dendritic substituents

The intra-molecular energy transfer in zinc (II) phthalocyanine bearing poly (aryl benzyl ether) dendritic substituents was studied by steady-state, time-resolved fluorescence and UV/Vis spectroscopy. The light-harvesting ability of this series of novel dendritic phthalocyanines increased with the dendron generation. Intra-molecular energy could be transferred from peripheral dendrons, as donors, to the phthalocyanine core, as an acceptor, during a photo-induced process. The intra-molecular energy transfer quantum yield also increased with the dendron generation. It was as high as 80% for the second generation of this dendritic phthalocyanine. Our study suggests that this novel dendritic phthalocyanine is an effective new energy transmission complex with high efficiency, and could be used as a potential light-harvesting system.

Main-chain hyperbranched polyrotaxane: Synthesis, photophysical properties, and energy funnel

A main-chain hyperbranched polyrotaxane (HBP) assembled by the interaction between dibenzo[24]crown-8 (DB24C8) and dibenzyl ammonium (DBA) was synthesized through Cu(I)-catalyzed azide-alkyne cycloaddition. Energy donors and acceptors were attached to DB24C8 and DBA units, respectively, to investigate the effect of such polyrotaxane structure on the intramolecular and intermolecular energy transfer channel. Our investigations indicated that HBP with higher molecular weight was obtained in relatively lower concentration. AFM, DLS, and SLS analyses revealed that our HBP molecule was described as a ball-shaped nanoparticle with the radius of about 4–8 nm. Benefitting from such unique topology, the aggregation of the chromophores through π-π stacking was effectively suppressed both in solution and in solid state. Meanwhile, the steady-state and time-resolved fluorescence characterization demonstrated that HBP exhibited the excellent energy funneling ability from A3 to B2 unit with high energy transfer efficiency and fast rate, which was attributed to the large spectral overlap between the emission features of the donors and the absorption of the acceptors, and the unique highly branched mechanically interlocked architecture. The energy transfer quantum yield of HBP was calculated to be as high as 99%, and this energy transfer process was estimated to occur with a rate of 7.58 × 109 s−1 with single exponential.

Biohybrid Photosynthetic Antenna Complexes for Enhanced Light-Harvesting

Biohybrid antenna systems have been constructed that contain synthetic chromophores attached to 31mer analogues of the bacterial photosynthetic core light-harvesting (LH1) β-polypeptide. The peptides are engineered with a Cys site for bioconjugation with maleimide-terminated chromophores, which include synthetic bacteriochlorins (BC1, BC2) with strong near-infrared absorption and commercial dyes Oregon green (OGR) and rhodamine red (RR) with strong absorption in the blue-green to yellow-orange regions. The peptides place the Cys 14 (or 6) residues before a native His site that binds bacteriochlorophyll a (BChl-a) and, like the native LH proteins, have high helical content as probed by single-reflection IR spectroscopy. The His residue associates with BChl-a as in the native LH1 β-polypeptide to form dimeric ββ-subunit complexes [31mer(-14Cys)X/BChl](2), where X is one of the synthetic chromophores. The native-like BChl-a dimer has Q(y) absorption at 820 nm and serves as the acceptor for energy from light absorbed by the appended synthetic chromophore. The energy-transfer characteristics of biohybrid complexes have been characterized by steady-state and time-resolved fluorescence and absorption measurements. The quantum yields of energy transfer from a synthetic chromophore located 14 residues from the BChl-coordinating His site are as follows: OGR (0.30) < RR (0.60) < BC2 (0.90). Oligomeric assemblies of the subunit complexes [31mer(-14Cys)X/BChl](n) are accompanied by a bathochromic shift of the Q(y) absorption of the BChl-a oligomer as far as the 850-nm position found in cyclic native photosynthetic LH2 complexes. Room-temperature stabilized oligomeric biohybrids have energy-transfer quantum yields comparable to those of the dimeric subunit complexes as follows: OGR (0.20) < RR (0.80) < BC1 (0.90). Thus, the new biohybrid antennas retain the energy-transfer and self-assembly characteristics of the native antenna complexes, offer enhanced coverage of the solar spectrum, and illustrate a versatile paradigm for the construction of artificial LH systems.

Effects of hydrogen bonding interaction and solvent polarity on the competition between excitation energy and photo-induced electron transfer processes in hydroxy(1-pyrenebutoxy)phosphorus(V)porphyrin

The solvent effects on an excitation energy transfer and a photo-induced electron transfer processes were examined using synthesized hydroxy(1-pyrenebutoxy)phosphorus(V)porphyrin. In the photoexcited state of the pyrene moiety, the intramolecular energy transfer to the porphyrin competed with the electron transfer from the pyrene to the porphyrin. The quantum yield of energy transfer in non-alcoholic solvents decreased with an increase of the solvent polarity due to the enhancement of electron transfer. However, the energy transfer was predominant process in alcoholic solvents with high polarity. The energy transfer yield increased with an increase in the ratio of methanol in the mixture of acetonitrile and methanol, of which solvent polarity is almost the same as that of acetonitrile. The redox potential measurements and ab initio molecular orbital calculation at Hartree-Fock 6-31G* level have shown that the electron affinity of the porphyrin moiety decreased through the hydrogen bonding with alcoholic solvents, resulting in that the electron transfer is suppressed and the excitation energy transfer becomes the predominant process. In conclusion, the hydrogen bonding interaction with alcoholic solvent contributes to the competition between energy and electron transfer by the changing of the energy level of charge transfer state rather than the effect of solvent polarity.

Effective Enlargement of Fluorescence Resonance Energy Transfer of Poly-Porphyrin Mediated by β-Cyclodextrin Dimers

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene bridged bis(permethyl-beta-cyclodextrins) 1 was synthesized successfully through click chemistry, and it forms a well-defined linear assembly with 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin 2 via extremely strong host-guest interactions, which was identified by the methods of UV-vis, NMR, AFM, and TEM, respectively. Furthermore, the fluorescence resonance energy transfer from host spacer to porphyrin guest was investigated, showing that the energy transfer quantum yield is high to 94% in virtue of such a noncovalent path.

Formation and energy transfer property of a subphthalocyanine–porphyrin complex held by host–guest interactions

A stable 2 : 1 host-guest complex is formed between a beta-cyclodextrin-conjugated subphthalocyanine and a tetrasulfonated porphyrin in water. The complex exhibits an energy transfer property from the excited subphthalocyanine to the porphyrin core with an excitation energy transfer quantum yield of 0.38.

Experimental and Theoretical Study of Triplet Energy Transfer in Rigid Polymer Films

With the judicious selection of triplet energy donor (D) and acceptor (A) pairs, a laser flash photolysis procedure has provided a sensitive method for the study of triplet energy transfer in rigid polymer films. By monitoring changes in triplet-triplet (T-T) absorptions the kinetics of triplet energy transfer were evaluated at short time scales, and overall energy-transfer quantum yields were also obtained. Combinations of xanthone- or thioxanthone-type donors and polyphenyl acceptors were particularly suited to these measurements because the former have high intersystem-crossing quantum yields and the latter have very high extinction coefficients for T-T absorption. For exothermic transfer most of the energy transfer that occurred within the lifetime of triplet D ( (3)D) took place in less than a few microseconds after (3)D formation in poly(methyl methacrylate), and triplet A yields were limited largely by the number of A molecules in near contact with (3)D. The kinetics of triplet energy transfer were modeled using a modified Perrin-type statistical arrangement of D/A separations with allowance for excluded volume in combination with a Dexter-type formula for the distance-dependent exchange energy-transfer rate constant. Experimental observations were best explained by constraining D/A separations to reflect the dimensions of intervening molecules of the medium. Rate constants, k 0, for exothermic energy transfer from (3)D to A molecules in physical contact are approximately 10 (11) s (-1) and very similar to triplet energy-transfer rate constants determined from solution encounters. Energy-transfer rate constants, k( r), fall off as approximately exp(-2 r/ 0.85), where r is the separation distance between D and A centers in angstroms. Exchange energy transfer is not restricted to (3)D and A in physical contact, but at </=0.4 M A at least 85% of the energy transfer arises from interaction of (3)D with a single nearest-neighbor A molecule. The modified Perrin model was also applied to quantum yields of quenching in rigid media. Comparison to the simple Perrin model for quenching shows that the latter may be adequate as long as molecular volumes are accommodated in the Perrin expression. Under these conditions the critical radius, r c, corresponds to the (3)D/A separation at which the effective rate constant for energy transfer equals the inverse of the (3)D lifetime.

Synthesis and Optical Properties of the Helical Oligonaphthalenes

We have developed an efficient synthesis method for optically active oligonaphthalenes (from 2 mer to 16 mer), which are connected at their 1,4-positions, under oxidative homo coupling with a stoichiometric amount of CuCl(2) and amines. The absolute configuration of the newly formed axis bond was determined based on the CD spectra of oligonaphthalenes with 1) two pyrene rings on the central naphthalenes or 2) two tetraphenylporphyrins (TPP) on the top and bottom naphthalenes. The fluorescence quantum yields increased as the number of naphthalene units increased in methoxy derivatives 10-12, and the intramolecular energy transfer quantum yields of bispyrene derivatives 7-9 were around 20% regardless of the number of naphthalene units. Furthermore, the hexadecanaphthalene derivative 4b with two TPPs exhibited a clear exciton coupling over an interchromophore distance to ca. 66 A.

Photophysical Properties of Near-Infrared-Emitting Ln(III) Complexes with 1-(9-Anthryl)-4,4,4-trifluoro-1,3-butandione (Ln = Nd and Er)

We report the synthesis and photophysical properties of Nd(III) and Er(III) complexes with 1-(9-anthryl)-4,4,4-trifluoro-1,3-butandione (9-ATFB). The complexes of [Nd(9-ATFB)4]- and [Er(9-ATFB)4]- produced sensitized near-infrared (NIR) luminescence via the excitation of anthracene. This suggests that the intramolecular energy transfer occurred from the singlet excited state of anthracene to the resonance levels of the metal ions, since the phosphorescence of anthracene is forbidden under normal conditions. The observed quantum yield of the visible luminescence showed that the energy transfer is more efficient for [Nd(9-ATFB)4]- than for [Er(9-ATFB)4]-. The lifetimes of the NIR luminescence of the complexes were in the microsecond range. The quantum yields of the sensitized NIR of the complexes were estimated using the lifetime and the energy-transfer quantum yield.

Optical properties of oligo(2,3-dioxyfunctionalized)naphthalenes

The properties of two series of oligo(2,3-dioxyfunctionalized)naphthalenes which are connected at the 1,4-positions, that is, methoxy derivatives 1– 4 and derivatives that possess two pyrene groups on the central scaffolding oxygen functions 5– 8 , are described. In 1– 4 , the fluorescence quantum yields increased by about 20–80% as the number of naphthalene units increased. The intramolecular energy transfer quantum yields of 5– 8 were around 20% regardless of the number of naphthalene units.

Synthesis and photochemical characterization of a zinc phthalocyanine–zinc porphyrin heterotrimer and heterononamer

The synthesis of two phthalocyanine-porphyrin covalently linked heteromolecules are described. Intramolecular energy transfer is investigated and quantified in terms of the quantum yield of energy transfer and found to be highly effective in both molecules. The photophysical properties of both molecules are modified greatly by the presence of the porphyrin moieties on the phthalocyanine core.