Long-wavelength Fluorescence Band Research Articles

Excimer Emission of Acridine Orange Adsorbed on Gadolinium-Yttrium Orthovanadate Nanoparticles.

Studying the complexes of inorganic nanoparticles - organic dye molecules is of great importance for their theranostics application. In this paper, we report gadolinium-yttrium orthovanadate nanoparticles (VNPs) - Acridine Orange (AO) complex formation in water solutions. To study the interactions between VNPs and AO, the methods of steady-state and time-resolved spectroscopy were used. It was shown that in aqueous solutions containing VNPs, AO aggregation takes place with a sandwich-like stacking of AO molecules in the near-surface layer of VNPs. The VNPs-AO complex formation causes significant changes in the AO fluorescence spectrum, namely, the appearance of a new broad, structureless band in the long-wavelength spectral edge, which was not observed in AO spectrum in a pure water solution. By analyzing of the absorption, fluorescence excitation spectra and fluorescence decay, the static excimer origin of the long-wavelength fluorescence band has been established.

Dynamic feedback of the photosystem II reaction centre on photoprotection in plants.

Photosystem II of higher plants is protected against light damage by thermal dissipation of excess excitation energy, a process that can be monitored through non-photochemical quenching of chlorophyll fluorescence. When the light intensity is lowered, non-photochemical quenching largely disappears on a time scale ranging from tens of seconds to many minutes. With the use of picosecond fluorescence spectroscopy, we demonstrate that one of the underlying mechanisms is only functional when the reaction centre of photosystem II is closed, that is when electron transfer is blocked and the risk of photodamage is high. This is accompanied by the appearance of a long-wavelength fluorescence band. As soon as the reaction centre reopens, this quenching, together with the long-wavelength fluorescence, disappears instantaneously. This allows plants to maintain a high level of photosynthetic efficiency even in dangerous high-light conditions.

Fluorescence quenching of the phycobilisome terminal emitter LCM from the cyanobacterium Synechocystis sp. PCC 6803 detected in vivo and in vitro

The fluorescence emission of the phycobilisome (PBS) core-membrane linker protein (LCM) can be directly quenched by photoactivated orange carotenoid protein (OCP) at room temperature both in vitro and in vivo, which suggests the crucial role of the OCP–LCM interaction in non-photochemical quenching (NPQ) of cyanobacteria. This implication was further supported (i) by low-temperature (77K) fluorescence emission and excitation measurements which showed a specific quenching of the corresponding long-wavelength fluorescence bands which belong to the PBS terminal emitters in the presence of photoactivated OCP, (ii) by systematic investigation of the fluorescence quenching and recovery in wild type and LCM-less cells of the model cyanobacterium Synechocystis sp. PCC 6803, and (iii) by the impact of dephosphorylation of isolated PBS on the quenching. The OCP binding site within the PBS and the most probable geometrical arrangement of the OCP–allophycocyanin (APC) complex was determined in silico using the crystal structures of OCP and APC. Geometrically modeled attachment of OCP to the PBS core is not at variance with the OCP–LCM interaction. It was concluded that besides being a very central element in the PBS to reaction center excitation energy transfer and PBS assembly, LCM also has an essential role in the photoprotective light adaptation processes of cyanobacteria.

Changes of the antenna of photosystem I induced by short-term heating

Changes in low-temperature fluorescence spectra of pea chloroplasts induced by the short-term heating were studied. Excitation spectra of the long-wavelength fluorescence were studied as well. Heating was carried out at 45°C for 5 min in the darkness or in the presence of white light sourced with intensities of 260 or 1400 μmol/m2 s. All variants of heating decreased the intensity of the long-wavelength fluorescence band. The integral of the excitation spectrum decreased after the exposure to heating in the darkness and increased after the exposure to heating in the presence of light. The observed changes in most intensive components — 726, 729 and 731 nm — of the long-wavelength fluorescence band, induced by various modes of heating, were similar. The changes in the fourth intensive component at 735 nm were different. Twenty-five components were found in the fine structure of the excitation spectrum of the long-wavelength fluorescence. Positions of most of peaks corresponded to the absorption peaks of Lhca proteins. Heat-induced changes in the excitation spectrum in the regions corresponding to the absorption of chl b and short-wavelength forms of chl a have been shown to correlate with changes in the intensities of the 726-, 729-, and 731-nm components of the long-wavelength fluorescence. This allows one to assign them to the emission of the outer antenna of Photosystem I. Changes in the intensity of the component at 735 nm correlated only with changes in excitation spectrum in the long-wavelength region that corresponded to the absorption of the long-wave-length forms of chlorophyll a. Therefore, the 735-nm component could be assigned to the emission of the Photosystem I inner antenna. Analysis of the changes induced by heating in the emission and excitation spectra of fluorescence revealed changes in the energy transfer in the outer and the inner antennas of Photosystem I. Heating in the darkness lowered the energy transfer in the outer and in the inner antennas. Both modes of heating in the presence of light increased the energy transfer in the outer antenna. For the inner antenna, presence of the light promotes an efficient of energy transfer at the levels close to the control one. It is proposed that illumination during heating exposure causes a specific state of the antenna complex in Photosystem I that provides an increase in funneling of the energy toward the reaction centers.

Spectral properties of anionic form of 3-hydroxyflavone

The spectral and temporal characteristics of the fluorescence of the anionic form of some 3-hydroxiflavones in different solvents are studied. This form is observed under selective excitation in the region of the long-wavelength slope of the main absorption band, and its spectrum consists of a wide structureless band lying between the short- and long-wavelength fluorescence bands of these molecular probes. The fluorescence excitation spectra of the anionic form differ from the corresponding spectra of the normal and tautomeric forms. The addition of water to the solution leads to a gradual fluorescence quenching which is static or belongs to the second kind according to Vavilov’s classification, i.e., occurs in the ground state.

Dynamic quenching of the multiband fluorescence of 3-hydroxyflavone

The properties of emission, absorption, and dual fluorescence excitation of 3-hydroxyflavone in acetonitrile are studied under the conditions of dynamic quenching by potassium iodide with concentrations up to 4 × 10−2 M. The normal and tautomeric forms undergo quenching, which is more efficient for the tautomeric form. An interesting circumstance is that the absorption in the S0 → S1 and S0 → S2 singlet bands of the solution increases with increasing quencher concentration in the whole region of concentrations used, the steepest rise being recorded in the concentration region from 0 to 5 × 10−3 M. The intensities and quantum yields of the two fluorescence bands show rather complicated nonlinear dependences on the quencher concentration. The long-wavelength fluorescence band, which belongs to the tautomeric form of 3-hydroxyflavone, is quenched considerably stronger. The experimental results reveal the kinetic character of the excited-state proton transfer in molecules of 3-hydroxyflavone in acetonitrile.

Influence of Silver Colloid Presence on Stilbazolium Merocyanine Emission

Absorption, fluorescence emission, and fluorescence excitation spectra of stilbazolium merocyanine (1-(n-butyl)-4[(3,5-dimethoxy-4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridyne) dye in water solution without and with colloidal silver addition were measured. In the presence of the colloid, besides the absorption band assigned to the protonated species of the dye (at 391 nm), an absorption band related to the free-base species appears at 490 nm. From the absorption and emission spectra, measured at various dye concentrations, follows that the aggregates are not effectively formed. Therefore, the long-wavelength absorption and fluorescence bands have to be related to some dye forms created by the solvatochromic effects. The fluorescence bands of the protonated and the free-base species are located at 559 nm and at about 630 nm, respectively. The shape of the long-wavelength band suggests the occurrence of more than one free-base form of the dye. At some dye and colloid concentrations, the global emission of the sample is enhanced as a result of silver addition. The increase in the emission yield of the dye could be partially due to not only the change in the concentrations of dye forms exhibiting various emission yields but is also due to the resonance surface plasmon effect. Because of the superposition of several effects, before the practical application of merocyanine as an indicator of metal presence in biological samples, its spectral properties in the system investigated should be established.

Multiple emitting species and competing intramolecular fluorescence quenching in 9,9′-dianthrylmethanol and model compounds

In addition to the anthracene-type emission, 9,9′-dianthrylmethanol (A1 OHA) shows a structureless long-wavelength fluorescence band, which undergoes a red-shift as well as an increase of its relative intensity with increasing solvent polarity. A parallel intramolecular fluorescence quenching process is investigated by the study of two reference compounds, 9-hydroxymethylanthracene and 9-ethoxymethylanthracene. In spite of the lack of the additional fluorescence band in this case, the quenching still persists. It might be caused by the formation of an intramolecular nonemissive exciplex but it cannot be the source for the observed additional red-shifted structureless emission band of the bichromophoric compound. The latter has been accounted for by a polar excited state product resulting from a charge separation process.

The origin of the long-wavelength fluorescence emission band (77°K) from photosystem I

Isolated photosystem I (PSI)-110 particles, prepared using a minimal concentration of Triton X-100 [ J. E. Mullet, J. J. Burke, and C. J. Arntzen (1980) Plant Physiol. 65, 814–822 ] and further subjected to short-term solubilization with sodium dodecyl sulfate (SDS), were resolved into four pigment-containing bands on polyacrylamide gel electrophoresis (PAGE). We have identified these in order of increasing electrophoretic mobility as being (a) CPIa, (b) CPI, (c) the light-harvesting complex of photosystem I (LHC-I), and (d) a free pigment-zone. LHC-I had an absorption maximum in the red at 668–669 nm and a shoulder at 650 nm, which was resolved by its first-derivative spectrum to indicate the presence of chlorophyll b. LHC-I exhibited a 77 °K fluorescence emission maximum at 729–730 nm. The 77°K fluorescence emission maxima of CPIa and CPI, excised from the gel, were at 729 and 722 nm, respectively. The LHC-I band, excised from the gel and rerun on dissociating SDS-PAGE, was resolved into two polypeptide doublets of 24-22.5 and 21-20.5 kDa. The CPIa band under similar conditions was resolved into polypeptides of 68, 24, 22.5, 21, 20.5, 19, 15, and 14 kDa; on the contrary, CPI contained only the 68-kDa polypeptide. When intact thylakoids were subjected to “nondenaturing” SDS-PAGE, LHC-I comigrated with an oligomeric form (dimer) of the light-harvesting chlorophyll a/b pigment-protein that preferentially serves photosystem II (LHCP-II). When this combined LHC-I/ LHCP-II pigment-protein band was prepared by SDS-PAGE from isolated stroma lamellae, it exhibited a long-wavelength fluorescence band near 730 nm at 77 °K. When a similar preparation was obtained from sucrose density gradients containing SDS [ J. Argyroudi-Akoyunoglou and H. Thomou (1981) FEBS Lett. 135, 171–181 ], it was found to be enriched in a 21-kDa polypeptide. The data suggest that the 21-kDa polypeptide of LHC-I is the chlorophyll-containing polypeptide responsible for the long-wavelength fluorescence of LHC-I; other polypeptides in the complex (20.5, 22.5, and 24 kDa) presumably bind chlorophyll and also serve an antennae function.

Energy transfer and distribution in the red alga Porphyra perforata studied using picosecond fluorescence spectroscopy

The detailed process of excitation transfer among the antenna pigments of the red alga Porphyra perforata was investigated by measuring time-resolved fluorescence emission spectra using a single-photon timing system with picosecond resolution. The fluorescence decay kinetics of intact thalli at room temperature revealed wavelength-dependent multi-component chlorophyll a fluorescence emission. Our analysis attributes the majority of chlorophyll a fluorescence to excitation originating in the antennae of PS II reaction centers and emitted with maximum intensities at 680 and 740 nm. Each of these fluorescence bands was characterized by two kinetic decay components, with lifetimes of 340–380 and 1700–2000 ps and amplitudes varying with wavelength and the photochemical state of the PS II reaction centers. In addition, a small contribution to the long-wavelength fluorescence band is proposed to arise from chlorophyll a antennae coupled to PS I. This component displays fast decay kinetics with a lifetime of approx. 150 ps. Desiccation of the thalli dramatically increases the contribution of this fast decay component.

Study of the long-wavelength fluorescence band at 920 nm of isolated reaction centers of the photosynthetic bacterium Rhodopseudomonas spaeroides R-26 with fluorescence-detected magnetic resonance in zero field

The triplet state of isolated reaction centers of Rhodopseudomonas sphaeroides R-26 has been studied by fluorescence-detected electron spin resonance in zero magnetic field (FDMR) at 4.2 K. The sign of the FDMR resonance monitored at the long-wavelength fluorescence band is positive (fluorescence increase); this confirms the earlier interpretation (Hoff, A.J. and Gorter de Vries, H. (1978) Biochim. Biophys. Acta 503, 94–106) that the negative sign of the FDMR resonance of the reaction center triplet state in whole bacterial cells is caused by resonant transfer of the singlet excitations from the antenna pigments to the trap. By monitoring the FDMR response as a function of the wavelength of fluorescence, we have recorded microwave-induced fluorescence spectra. In addition to the positive microwave-induced fluorescence band peaking at 935 nm, at 905 nm a negative band was found. The resonant microwave frequencies for these two bands, i.e., the values of the zero-field splitting parameters | D| and | E| of the triplet state being monitored, were different, those of the 905 nm microwave-induced fluorescence band being identical to the resonant microwave frequencies measured with absorption-detected zero-field resonance (Den Blanken, H.J., Van der Zwet, G.P. and Hoff, A.J. (1982) Chem. Phys. Lett. 85, 335–338), a technique that monitors the bulk properties of the sample. From this result and its negative sign, we tentatively attribute the 905 nm microwave-induced fluorescence band to a small (possibly less than 1%) fraction of antenna bacteriochlorophylls that are in close contact with the trap. The positive 935 nm microwave-induced fluorescence band with resonant microwave frequencies deviating from the bulk material is ascribed to a minority of primary donor bacteriochlorophyll dimers, which have a higher than normal fluorescence yield because of a somewhat slower charge-separation reaction. Is it likely that practically all long-wavelength fluorescence of isolated reaction centers stems from such impaired reaction centers.

Luminescence Properties and the Primary Process of Photochromism of 2-(2-Hydroxyphenyl)benzothiazole

Abstract The luminescence behavior of 2-(2-hydroxyphenyl)benzothiazole at 77 K was studied in detail, special attention being paid to dual fluorescence at ≈500 and ≈370 nm and also to phosphorescence at ≈500 nm. From the dependence of these emission bands upon the hydrogen-bonding ability of solvents and the excitation spectra, it is concluded that the short- and long-wavelength fluorescence bands are due to the intermolecularly hydrogen-bonded enol imine and the keto amine produced from the intramolecularly hydrogen-bonded enol, respectively, and that the phosphorescence is due to the intermolecularly hydrogen-bonded enol imine. The estimated quantum yield of the enol fluorescence gives further support to the formation scheme of the photochromic colored species previously presented. The rate constants of the intramolecular hydrogen transfer at 77 and 293 K are evaluated to be larger than 4×1010 s−1 and 3×1012 s−1, respectively.

Intermediates and Kinetics of Fluorescence Quenching by Electron Transfer

AbstractA structureless, longwavelength fluorescence band, attributed to the excited (charge‐transfer) complex: A−D+, occurs when the fluorescence of aromatic hydrocarbons (A) is quenched by aryl amines (D). The relative intensity of this band is found to decrease strongly with increasing solvent polarity, so that ultimately in highly polar solvents (ε > 30) no complex emission can be observed even at high aryl amine concentration at which the normal hydrocarbon fluorescence is strongly quenched.Flash experiments carried out with solutions of aromatic hydrocarbons in acetonitrile (ε = 37) with high concentrations of diethylaniline show transient absorption spectra which are due to the triplet state of the hydrocarbon and to the radical ions A·− and D+ which are produced with quantum yields between 2 and 6%. Kinetic experiments (of fluorescence quenching) indicate that in polar solvents electron transfer can occur at an encounter distance of about 7 Å. A kinetic scheme which is consistent with these results and meets the energetic requirements is discussed.