Triplet-singlet Energy Transfer Research Articles

Fluorescence quenching in a strongly helical peptide series: the role of noncovalent pathways in modulating electronic interactions.

The very strong helical propensity of peptides rich in alpha-aminoisobutyric acid (Aib) has enabled the design of a set of helices containing as guest amino acids one fluorescent chromophore, beta-(1'-naphthyl)-L-alanine, and one heavy atom perturber, p-bromo-L-phenylalanine. The fluorescence of the chromophoric residue was monitored in this set to explore heavy atom induced enhanced intersystem crossing as a potentially useful tool for exploring remote electronic interactions in biomolecules. The peptides in this set were sequence isomers of each other and were designed such that the chromophore and the perturber were separated by two, one, or zero Aib residues. The respective distances between the aromatic side chains are then modulated by the twist of the helix. All peptides showed steady-state fluorescence quenching, and on the basis of further time-resolved triplet-triplet absorption experiments, two mechanisms for the heavy atom induced fluorescence quenching were established: (i) a weak and nominally spin-forbidden singlet-triplet energy transfer and (ii) the remote heavy atom effect (RHAE) on the intersystem crossing within the fluorophore. Both the rate of singlet-triplet energy-transfer and the RHAE are at their maxima in the peptide with the largest sequence separation but the smallest direct distance between the chromophore and the perturber. Thus neither quenching mechanism is controlled by the length of the intervening covalent pathway. Subtle factors arising from the structure of the intervening peptide backbone apparently contribute to the RHAE for the peptides with shorter sequence separation. Because the sensitivity to the remote heavy atom is a measure of electronic delocalization, this result may have significance for the understanding of the role of helices in biological electron-transfer interactions.

Characterization of tryptophan phosphorescence of aspartate aminotransferase from Escherichia coli.

The Trp phosphorescence spectrum, intensity and decay kinetics of apo-aspartate aminotransferase, pyridoxamine-5P-aspartate-aminotransferase and pyridoxal-5P-aspartate aminotransferase were measured over a temperature range 160-273 K. The fine structure of the phosphorescence spectra in low-temperature glasses, with 0-0 vibrational bands centered at 408, 415 and 417 nm, for both apoenzyme and pyridoxamine-5P-enzyme reveals a marked heterogeneity of the chromophore environments. Only for the pyridoxal-5P form of the enzyme is the triplet emission strongly quenched and, in this case, the spectrum displays a unique 0-0 vibrational band centered at 415 nm. Concomitant to quenching, there is Trp-sensitized delayed fluorescence of the Schiff base, an indication that quenching of the excited triplet state is due, at least in part, to a process of triplet singlet energy transfer to the ketoenamine tautomer. All three forms of the enzyme are phosphorescent for temperatures up to 273 K. However, across the glass transition temperature the pyridoxal-5P enzyme shows a decrease in lifetime-normalized phosphorescence intensity, a thermal quenching that reduces even further the number of phosphorescing residues at ambient temperature. In fluid solution, the triplet decay is nonexponential and multiple lifetimes stress the heterogeneity in dynamical structure of the chromophores' sites. For the pyridoxal-5P enzyme, where only one or at most two residues are phosphorescent at 273 K, the nonexponential nature of the decay implies the presence of different conformers of the protein not interconverting in the millisecond time scale.

Characterization of tryptophan and coenzyme luminescence in tryptophan synthase from Salmonella typhimurium.

Tryptophan synthase from Salmonella typhimurium is a bifunctional alpha 2 beta 2 complex that catalyzes the formation of L-tryptophan. We have characterized over the temperature range from 160 to 293 K the fluorescence and phosphorescence properties of the single tryptophan present at position 177 of the beta-subunit and of the pyridoxal 5'-phosphate bound through a Schiff's base in the beta-active site. The comparison between the fluorescence of the pyridoxal phosphate bound either to the protein or to valine free in solution indicates substantial protection for the coenzyme against thermal quenching and a greater intensity of the ketoenamine tautomer band. Trp-177 is highly luminescent, and its proximity to the pyridoxal moiety leads to an over 50% quenching of its fluorescence with both reduced and native coenzyme. The Trp phosphorescence spectrum possesses a narrow, well-defined, 0-0 vibrational band centered at 418.5 nm, a wavelength that indicates strong polar interactions with neighboring charges. The observation of delayed fluorescence in the native complex implies that the excited triplet state is involved in a process of triplet-singlet energy transfer to the ketoenamine tautomer. The rate of energy transfer, heterogeneous in low-temperature glasses with rate constants of 2.26 and 0.07 s-1, becomes homogeneous in fluid solutions as the coenzyme tautomer interconversion is likely faster than the phosphorescence decay. In both apo- and holo-alpha 2 beta 2, the phosphorescence from Trp-177 is long-lived even at ambient temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Intermolecular energy transfer in mixed laser dyes: photophysical properties of triplet states

Triplet-singlet energy transfer in laser dyes have been studied in EPA at 77K using N2 laser as an excitation source. Phosphorescence of the donor (D) and the delayed fluorescence of the acceptor (A) and their lifetimes have been measured for coumarin 102 (D)-rhodamine B(A) and 9(10H)-acridone (D)-rhodamine 6G(A) dye systems as a function of acceptor concentration. These data yield energy transfer rate constants of ∼103 dm3 mol−1 s−1 for the donor acceptor combinations, consistent with the Forster mechanism. The phosphorescence quantum efficiency and other spectral parameters are also reported.

Quenching of Excited Singlet and Triplet States of Some Polyfused Arenes by Dihalobenzenes

Abstract External heavy atom effect on the emission spectra of naphthalene, phenanthrene, and chrysene by perturbers dihalobenzenes are investigated to estimate different nonradiative rate constants associated with the depletion of the singlet and the triplet states of the fluorescers. The bimolecular fluorescence quenching rate constant kq has been evaluated at 300 K by applying Stern–Volmer relation. The dihalobenzene quenchers have triplet states lying below the singlet states of the fluorescers and the overall quenching rate kq is composed of two rate constants, namely, the intramolecular intersystem crossing rate kqISC and the singlet–triplet energy transfer rate constant kqST. The relative magnitudes of the two rate constants kqISC and kqST have been examined in the light of the energy conditions controlling the associated processes. At 77 K, the phosphorescence decay curve of the fluorescers in the presence of dihalobenzenes is biexponential and the triplet decay of the perturbed fraction of the fluorescers is exponential. It is concluded that at the low temperature, heavy atom interaction in the systems studied mainly proceeds through CT mechanism. Speculative suggestion has been made to account for enhancement of phosphorescence emission of polyfused arenes in EtOH solution.

Role of contact complexes in singlet-triplet energy transfer

(T-T) energy transfer from the acceptor to donor. If the properties of the solvent cage lead to the same probability for these two energy transfer processes between donor and acceptor molecules, there should be no accumulation of triplet acceptor molecules in solution. In this case, acceptor molecules act as a catalyst leading to an increased population of triplet donor states. In addition to the above scheme of energy conversion in a contact complex, one can also expect that during the lifetime of the solvent cage only the S-T stage of electronic energy transfer will be completed. In this case the excited complex decays before the reverse T-T energy transfer from the acceptor to donor takes place and therefore there is a high probability that the unreacted triplet acceptor molecules will migrate beyond the boundary of the solvent cage. Therefore, depending on whether or not the triplet acceptor molecules are found in solution, one can make a conclusion about the number of elementary steps responsible for the electronic excitation energy conversion in a contact complex during its lifetime in the solvent cage. Answering the above-mentioned questions is important for understanding the properties of the solvent cage and mechanisms of energy conversion in excited contact complexes. Therefore, we conducted studies on decay channels for contact complexes, in which one of the partners from a pair was in the singlet excited state. In order to simplify the problem as much as possible and reduce it to considering only two processes: the S-T energy transfer from the donor to acceptor and the reverse T-T energy transfer from the acceptor to donor, the excited complex must fulfill a number of conditions. One of them is the lack of overlap between the fluorescence spectrum of donor and the absorption spectrum of acceptor. The fulfillment of this condition allows us to neglect the sing!et-singlet (from SoD to SoA) energy transfer relative to the efficiency of S-T energy transfer between donor and acceptor. Moreover, some experimental data [i] indicate that the donor triplet level TiD of the studied pair should be considerably lower than the acceptor triplet level TiA (AE T > i000 cm-i). The larger the energy difference between TiD and TiA , the higher the probability of appearance of acceptor molecules in the triplet state in solution at the expense of S-T energy transfer relative to the probability of T-T energy transfer from the donor to acceptor.

Triplet-singlet energy transfer in the complex of auramine O with horse liver alcohol dehydrogenase.

Triplet-singlet energy transfer has been studied in the complex formed between auramine O (AO) and horse liver alcohol dehydrogenase with optically detected magnetic resonance (ODMR) spectroscopy. The results show that Trp-15 and Tyr residues transfer triplet energy mainly by a trivial process, whereas Trp-314 transfers triplet energy by a Förster process with two observed lifetimes at 77 K of 170 and 50 ms. The different Förster energy-transfer lifetimes are ascribed either to quenching of the two Trp-314 residues of the dimer by a single asymmetrically bound AO or to two distinct conformations of the enzyme-dye complex with differing separations and/or orientations of donor and acceptor. Individual spin sublevel transfer rate constants are reported for the major decay component with the 170-ms Trp triplet-state lifetime; these are found to be highly selective with kxtr much greater than kytr and kztr.

Experimental study of singlet-triplet energy transfer in liquid solutions

It has been found that fluorescence quenching of 9,10-dibromo-,9,10-dichloro-and 9,10-dicyano-anthracene by aromatic hydrocarbons is due not to singlet-triplet energy transfer but to donor-acceptor interactions leading to the formation of short-lived exciplexes. The 9,10-dicyanoanthracene exciplexes fluoresce and their radiationless deactivation occurs via population of the dicyanoanthracene triplet state. The decay of exciplexes of halo-anthracenes with arenes due to the heavy-atom effect occurs exclusively via intersystem crossing to the halo-anthracene triplet state.

Studies on triplet-singlet energy transfer with 1,3-dibromo-9,10-bis-[phenylethynyl]-anthracene

Benzophenon triplet sensitizes the fluorescence from the title compound by direct triplet-singlet energy transfer while sensitize fluorescence from the non-brominated analog results from biphotonic triplet-triplet annihilation following triplet-triplet energy transfer.

Nature of phototransformation of phytochrome As probed by intrinsic tryptophan residues.

The phototransformation of the photomorphogenic photoreceptor phytochrome was probed by the intrinsic luminescence of the tryptophan (Trp) residues. The red light absorbing form of phytochrome (Pr) showed a decreased tryptophan phosphorescence intensity, compared to that of the far-red light absorbing form of phytochrome (Pfr), and a delayed fluorescence from the chromophore upon excitation of the tryptophan residues with 290-nm light. The tryptophan phosphorescence in both Pr and Pfr showed decreased lifetimes (0.29 and 1.84 s, respectively) compared to that of the free tryptophan (6.00 s). In addition, the decay kinetics of the delayed fluorescence in Pr showed a short-lifetime component (0.24 s), which is similar to the tryptophan phosphorescence lifetime value. This is due to an efficient triplet-singlet (3Trp-1Pr) energy transfer in the Pr from. The increases in the tryptophan phosphorescence quantum yield and lifetime in the Pfr form have been interpreted on the basis of chromophore reorientation on the protein surface as a result of the Pr lead to Pfr phototransformation. The Stern-Volmer plot of the quenching data further confirms preferential exposure of the tryptophan residues in the Pfr form (46% "exposed' tryptophan residues in the Pr form as compared to 72% in the Pfr form). These results provide strong support for the hydrophobic model of Pfr [Hahn, T. R., & Song, P. S. (1981) Biochemistry 20, 2602-2609).

Quenching of the Yt-Base Fluorescence by Heavy-Atom Induced Intermoleeular Singlet-Triplet Energy Transfer

Quenching of the Yt-base fluorescence by a series of halogen derivatives of benzene and naphthalene was measured in dioxane. For the naphthalene derivatives, the presence of the heavy atom in the acceptor molecule was found to affect strongly the fluorescence quenching rate constant, whereas no such effect was observed for the benzene derivatives. The fact is explained with the assumption of a singlet-triplet energy transfer from the Yt- base molecules to the naphthalene derivatives

Platinum phthalocyanine symmetry and singlet-triplet energy transfer from electronic and vibronic Shpol'skii spectra

We report the first experimental study and detailed analysis of the structures in the phosphorescence, phosphorescence excitation, absorption, and resonance Raman spectra of platinum phthalocyanine (PtPc) in Shpol'skii matrices consisting of alphachloronapthalene (α-CIN) and n-octane. The studies were done at temperatures down to 1.5 K. From the data reported we arrive at a number of new observations, the principal ones being: (1) The confirmation that the molecular symmetry of PtPc in the ground as well as in the excited singlet and triplet states is less than D4h. (2) The identification of two additional radiative electronic triplet states at energies lower than the previously reported ones, as well as an additional excited electronic singlet state. (3) Information on splittings, vibronic transitions, intersystem crossing mechanisms, solvent and site effects, and potential surfaces, some of it in considerable detail.

THE MECHANISM OF THE 9,10‐DIBROMOANTHRACENE MEDIATED TRIPLET‐SINGLET ENERGY TRANSFER IN THE TETRAMETHYL‐1,2‐DIOXETANE ENERGIZED RUBRENE LUMINESCENCE*

Abstract— The ternary chemiluminescent system consisting of tetramethyl‐dioxetane (TMD), 9,10‐dibromoanthracene (DBA) and rubrene (Ru) has been investigated in benzene solution and in polystyrene matrices. DBA has been found to mediate the energy transfer between excited triplet acetone (3K), generated from TMD, and rubrene resulting in the enhancement of the Ru emission and reduction in the DBA emission. A detailed kinetic analysis confirms that ca. 50% of the enhanced chemilumines‐cence involves triplet‐singlet (TS) energy transfer from 3K to DBA, followed by singlet‐singlet (SS) energy transfer from DBA to Ru, the remainder ca. 50% being due to reabsorption of DBA fluorescence by rubrene. It is concluded that the TS energy transfer is of the resonance type, occurring with a rate of kTSK.DBA= (1.4 ± 0.4) ± 109M‐1s‐1 and an efficiency of øTSK.DBA= 0.3 ± 0.1. As expected, the SS energy transfer is also of the resonance type, taking place at comparable rates in benzene solution and in polystyrene matrices, is. kSSDBARU= 1.5 ± 1010 M‐1 and (2.2 ± 0.2) ± 1010M‐1s‐1, respectively.

Electronic excitation transfer in polymers. 3. Singlet-singlet, triplet-singlet, and triplet-triplet energy transfers. Evidence for triplet migration among pendant phenyl groups of polystyrene

Chemiluminescent techniques have been employed to investigate electronic energy transfer from ketone donors (ace- tone, acetophenone) to acceptors (e.g., 9,lO-diphenylanthracene and biphenyl) in films of polystyrene and polymethyl methac- rylate at 50 C. Tetramethyl-l,2-dioxetane and 3,4-diphenyl-3,4-dimethyldioxetane were used to generate excited (singlet and triplet) acetone and (triplet) acetophenone, respectively. Analysis of quenching data in terms of the Perrin, Forster, or Dexter models all yielded critical transfer radii, R,, in the range of 23-29 8, for singlet-singlet and for triplet-singlet energy transfer. For triplet-triplet energy transfer, the values of R, were in the range of 11-17 8, with the exception of the acetone triplet to 1,4-dibromonaphthalene transfer in polystyrene, for which R, = 21 8,. Evidence is presented which supports the postulate that triplet energy migration among the pendant phenyl groups on the polystyrene backbone may cause unexpectedly large R, values for triplet-triplet energy transfer.

Study of triple-singlet energy transfer in an enzyme-dye complex using optical detection of magnetic resonance.

We have made optical detection of magnetic resonance (ODMR) measurements on the enzyme alpha-chymotrypsin, as well as on its complex with the dye, proflavin. Evidence that triplet-singlet energy transfer occurs in the complex is provided by the observation of characteristic tryptophan ODMR signals while monitoring the delayed fluorescence of the dye. The luminescence decay kinetics of the complex indicates that nontrivial triplet-singlet transfer originates from several (at least three) tryptophan residues of the enzyme. ODMR sensitivity can be enhanced by coupling the sublevels of a weakly radiative triplet state to a fluorescent dye which satisfies Förster's (Förster, T. (1948), Ann. Phys. (Leipzig) 2, 55; (1965), in Modern Quantum Chemistry, Istanbul Lectures, Part III, Sinanoglu, O., Ed., New York, N.Y., Academic Press, p 93) conditions for energy transfer.

Triplet-singlet radiationless energy transfer between benzophenone and perylene in vitreous solution

We have measured at 77 K the “critical radius” R 0 of the resonant intermolecular energy transfer from the triplet state of benzophenone to the singlet state of perylene, these two comporents being in vitreous solution.

Radiationless intermolecular singlet-triplet energy transfer in chlorophyll-a: tool for investigation of non-phosphorescing triplet states

Fluorescence quenching in chlorophyll- a induced by radiationless intermolecular singlet-triplet energy transfer is reported. The process may have important photochemical implications. A two-laser excitation procedure is employed to observe the quenching. The method complements fluorescence spectroscopy for measurement of fast intramolecular relaxation processes.

Triplet–singlet energy transfer in solution

In contrast to earlier work, no detectable triplet–singlet dipole–dipole energy transfer was found to occur in fluid solution; the reasons are briefly discussed.

Viscosity dependence of triplet-singlet energy transfer in solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTViscosity dependence of triplet-singlet energy transfer in solutionDavid M. Hercules and Anthony F. VaudoCite this: J. Am. Chem. Soc. 1971, 93, 11, 2599–2602Publication Date (Print):June 1, 1971Publication History Published online1 May 2002Published inissue 1 June 1971https://doi.org/10.1021/ja00740a004RIGHTS & PERMISSIONSArticle Views59Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (454 KB) Get e-Alerts Get e-Alerts

Fluorescent probes of biological membranes.

FLUORESCENT AND PHOSPHORESCENT PROBES THAT HAVE READILY INTERPRETABLE EMISSION PROPERTIES CAN BE SPECIFICALLY INSERTED INTO BIOLOGICAL MACROMOLECULES TO REVEAL FACETS OF THEIR STRUCTURE AND DYNAMICS: (1) Proximity. Singlet-singlet and triplet-singlet energy transfer can serve as spectroscopic rulers in the 10-65 A range, whereas triplet-triplet transfer can be used to show that two groups are less than about 12 A apart. (2) Rotational mobility. Nanosecond fluorescence polarization measurements can reveal whether a macromolecular system has any modes of flexibility in times of nanoseconds. (3) Polarity. The presence of mobile dipoles in the environment of certain chromophores is reflected in their fluorescence quantum yield and emission spectrum. We have synthesized a number of new fluorescent probes for biological membranes. Anthroyl stearic acid (I), dansyl phosphatidyl ethanolamine (II), and octadecyl naphthylamine sulfonic acid (III) are readily incorporated into bilayer vesicles composed of phosphatidyl choline. The emission spectra of these probes in the vesicles indicate that the chromophore of I is located in the hydrocarbon region, that of II is located in the glycerol layer, and that of III is located at the aqueous interface of the bilayer. Thus, fluorescent chromophores can be selectively placed in different transverse regions of a model membrane system.