Studies of the Energy Transfer among Allophycocyanin from Phycobilisomes of Polysiphonia urceolata by Time-Resolved Fluorescence Isotropic and Anisotropic Spectroscopy

Abstract— The excitation energy transfer processes in the allophycocyanin (APC) monomer and trimer from phycobilisomes of Polysiphonia urceolata were studied using picosecond time-resolved fluorescence isotropic and anisotropic spectroscopy. Based on our experimental results, conclusions could be drawn as follows: (1) After the processes of exciton localization are finished, the localized excitation energy on any chromophore can be transferred to the other chromophores due to the weak couplings between them, and the processes among three p₈₄-phycocyaninbilin (PCB) chromophores in the center of the ring shape of the APC trimer are more important than those of between a₈₄- and p₈₄-PCB chromophores in the same monomer. (2) The decay time constants of 95 ± 5 ps and 40 ± 5 ps components, observed by us in this work, were assigned to the excitation energy transfer or redistribution between α₈₄- and β₈₄-PCB chromophores in the same monomer of the APC trimer and among three β₈₄-PCB chromophores in the center of the ring shape of the APC trimer, respectively. Specifically, the assignment of the decay constants for the 40 ± 5 ps component was different from those of previous results. (3) Based on the model of Debreczeny, and using the fluorescence residual anisotropy r(∞) with a probing wavelength of 650 nm, the angles between the C₃ symmetry axis and transition dipoles of α₈₄- and -PCB chromophores were found to be φ_a84= 67° and φ_β84= 148°, respectively, which are in agreement with the prediction of the X-ray crystal structure of APC. (4) The results show that anisotropy decays, observed with the APC trimer, did exhibit a strongly probing wavelength dependence that did not show up in the monomer.     

Ultrafast spectroscopy studies on the mechanism of electron transfer and energy conversion in the isolated pseudo ginseng, water hyacinth and spinach chloroplasts

The spectroscopy characteristics and the fluorescence lifetime for the chloroplasts isolated from the pseudo ginseng, water hyacinth and spinach plant leaves have been studied by absorption spectra, low temperature steady-state fluorescence spectroscopy and single photon counting measurement under the same conditions and by the same methods. The similarity of the absorption spectra for the chloroplasts at room temperature suggests that different plants can efficiently absorb light of the same wavelength. The fluorescence decays in PS II measured at the natural QA state for the chloroplasts have been fitted by a three-exponential kinetic model. The three fluorescence lifetimes are 30, 274 and 805 ps for the pseudo ginseng chloroplast; 138, 521 and 1494 ps for the water hyacinth chloroplast; 197, 465 and 1459 ps for the spinach chloroplast, respectively. The slow lifetime fluorescence component is assigned to a collection of associated light harvesting Chl a/b proteins, the fast lifetime component to the react     

Excitation energy-transfer processes between two trimers in C-phycocyanin hexamer from the cyanobacterium Anabaena variabilis. Investigation by group theory and time-resolved fluorescence spectroscopy

We have employed group theory and picosecond time-resolved fluorescence isotropy and anisotropy spectroscopy methods to explore the excitation transfers within an isolated C-phycocyanin (C-PC) hexamer (αβ)₆^PCL²⁷_RC, situated at the end of the rod proximal to the core of the pycobilisome (PBS) in the cyanobacterium Anabaena variabilis. The group-theory results imply that excitation energy transfer between two trimers occurs between the lowest exciton level of each trimer. The excitation energy-transfer process might occur at a rate of 10–20 ps, and it may be described by an exciton hopping-like Förster transfer mechanism. Dynamic components of 45–50 ps are assigned to the excitation transfer from β₁₅₅-PCB chromophores to the exciton states of dimers, which consist of two neighbouring monomers of the same trimer in an isolated C-PC hexamer.     

Interligand energy transfer in europium(III) mesogenic adducts

An analysis of the absorption and luminescence spectra and luminescence kinetics showed that in the Eu(DK)₃bpy_17-17 mesogenic adduct, 5,5′-diheptadecyl-2,2′-bipyridine (bpy_17-17) took an active part in the energy transfer to the Eu³⁺ ion. The interligand energy transfer from β-diketonate (DK) ligands was the major mechanism of excitation of bpy_17-17. Importantly, the interligand excitation complex considerably decreased radiation losses during the energy transfer from the absorbing DK ligands to the emitting level of Eu³⁺.     

Direct Vibrational Energy Transfer in Monomeric Water Probed with Ultrafast Two Dimensional Infrared Spectroscopy

Vibrational relaxation dynamics of monomeric water molecule dissolved in d-chloroform solution were revisited using the two dimensional Infrared (2D IR) spectroscopy. The vibrational lifetime of OH bending in monomeric water shows a bi-exponential decay. The fast component (T₁=(1.2±0.1) ps) is caused by the rapid population equilibration between the vibrational modes of the monomeric water molecule. The slow component (T₂=(26.4±0.2) ps) is mainly caused by the vibrational population decay of OH bending mode. The reorientation of the OH bending in monomeric water is determined with a time constant of τ=(1.2±0.1) ps which is much faster than the rotational dynamics of water molecules in the bulk solution. Furthermore, we are able to reveal the direct vibrational energy transfer from OH stretching to OH bending in monomeric water dissolved in d-chloroform for the first time. The vibrational coupling and relative orientation of transition dipole moment between OH bending and stretching that effect their intra-molecular vibrational energy transfer rates are discussed in detail.     

PICOSECOND FLUORESCENCE KINETICS and ENERGY TRANSFER IN THE ANTENNA CHLOROPHYLLS OF GREEN ALGAE*

Single-photon timing measurements on flowing samples of Chlorella vulgaris and Chlamydomonas reinhardtii at low excitation intensities at room temperature indicate two main kinetic components of the fluorescence at open reaction centers (F₀) of photosystem II with lifetimes of approx. 130 and 500 ps and relative yields of about 30 and 70%. Closing the reaction centers progressively by preincubation of the algae with increasing concentrations of 3-(3′,4′-dichlorophenyl)-l,l-dimethylurea (DCMU) and hydroxylamine gave rise to a slow component with a lifetime increasing from 1.4 to 2.2 ns (F_max) The yield of the slow component increased to 65-68% of the total fluorescence yield in parallel to a decrease in the yield of the fast component to a value close to zero at the f_max-level. The 130 ps lifetime of the fast component remained unchanged. The middle component showed an increase of its lifetime from 500 to 1100 ps and of its yield by a factor of 1.5. Spacing of the ps laser pulses by 12 μs allowed us to resolve a new long-lived fluorescence component of very small amplitude which is ascribed to a small amount of chlorophyll not connected to functional antennae. The opposite dependence of the yield of the fast and the slow component on the state of the reaction centers at almost constant lifetimes is consistent with a mechanism of energy conversion in largely separately functioning photosystem II units. Yields and lifetimes of these two components are in agreement with the high quantum yield of photosynthesis. The lower lifetime limit of 1.4 ns of the slow component is assigned to the average transfer time of an excited state from a closed to a neighboring open reaction center and the increase in the lifetime to 2.2 ns is evidence for a limited energy transfer between photosystems II. Relative effects of changing the excitation wavelength from 630 to 652 nm on the relative fluorescence yields of the kinetic components were studied at the fluorescence wavelengths 682, 703 and 730 nm. Our data indicate that (i) the middle component has its fluorescence maximum at shorter wavelength than the fast component and (ii) that the antennae chlorophylls giving rise to the middle component are preferentially excited by 652 nm light. It is concluded that the middle component originates from the light-harvesting chlorophyll alb protein complexes and the major portion of the fast component from the chlorophyll a antennae of open photosystem II reaction centers.     

Effect of the solvent composition in methanol-pentane and methanol-acetonitrile mixtures on the spectral and luminescent properties of 1,2-dihydroquinolines

The dependence of absorption and fluorescence spectra, quantum yields, and lifetimes of fluorescence on the solvent composition in the MeOH-C₅H₁₂ and MeOH-MeCN mixtures was studied for 2,2,4,6-tetramethyl-1,2-dihydroquinoline (TMDHQ). The variations in the parameters of deconvolution of the absorption and fluorescence spectra by the Gaussian functions in the MeOH-C₅H₁₂ mixtures of various compositions indicate the specificity of methanol clustering in saturated hydrocarbons and hydrogen bonding between TMDHQ and the methanol clusters of different compositions. At low MeOH concentrations (∼0.2 vol %), TMDHQ molecules are practically completely bound with the MeOH molecules by hydrogen bonds. In the MeOH-MeCN mixtures, the changes in the absorption and fluorescence spectra are observed at a substantially higher MeOH concentration (≥10 vol %) and monotonically change at the further increase in the MeOH concentration that is caused by the peculiarities of MeOH clustering in acetonitrile and the distribution of the TMDHQ molecules between the solvent components. At 50–95 vol % of MeOH in the mixture with MeCN, the fluorescence decay kinetics is described by the biexponential curve with the lifetime of the major component (τ₁) decreasing from 7.5 to 1.1 ns in pure MeCN and MeOH, respectively, and the lifetime of the minor component τ₂ ≈ 4 ns corresponding to the fluorescence lifetime in the solution containing 50 vol % MeOH. This indicates the existence of the free TMDHQ molecules, which are not bound with MeOH molecules or their clusters.     

Long-lived Triplet Excited State of Perylenemonoimide (PMI) in a Diimine Pt(II) Bis-acetylide Complex: Preparation and Study of the Photophysical Property with Transient Spectra

We prepared a N^N Pt(II) bisacetylide complex that has strong absorption of visible light (molar absorption coefficients ϵ=6.7×10⁴ M⁻¹ cm⁻¹ at 570 nm), and the singlet oxygen quantum yield (Φ_Δ) is up to 78 %. Femtosecond transient absorption spectra show the intersystem crossing (ISC) of the complex takes 81.8 ps, nanosecond transient absorption spectra show the triplet excited state lifetime is 7.6 μs. Density functional theory (DFT) computation demonstrated that the S₁ and T₁ states are mainly localized on the perylenemonoimide (PMI) ligands, although the involvement of the Pt(II) centre is noticeable. The complex was used as triplet photosensitizer to generate delayed fluorescence with perylenebisimide (PBI) as the triplet state energy acceptor and emitter, via the intermolecular triplet-triplet energy transfer (TTET) and triplet-triplet annihilation (TTA), the delayed fluorescence lifetime is up to 52.5 μs under the experimental conditions.     

Study on inclusion complexes of meso-tetrakis(2-thienyl)porphyrin and Cu-meso-tetrakis(2-thienyl)porphyrin with cyclodextrins by spectroscopy method

In phosphate buffer solution of pH5.4, the interaction of meso-tetrakis(2-thienyl)porphyrin(H₂TTP) and Cu-meso-tetrakis(2-thienyl)porphyrin(Cu-TTP) with α-cyclodextrin(α-CD), β-CD, γ-CD, heptakis(2,3,6-tri-O-methyl)-β-CD(TM-β-CD) has been studied by means of UV-vis, fluorescence and ¹HNMR spectroscopy, respectively. The H₂TTP and Cu-TTP can form 1:2 inclusion complexes with TM-β-CD and 1:1 inclusion complexes with the other three cyclodextrins. In this paper, the inclusion constants (K) of H₂TTP and Cu-TTP for the formation of the inclusion complexes have been estimated from the changes of absorbance and fluorescence intensity in phosphate buffer solution. The inclusive capabilities of different kinds of cyclodextrins are compared. The result shows that the inclusion ability of α-CD with H₂TTP and Cu-TTP is the strongest among the three native CDs. The inclusion ability of modified β-CD with H₂TTP and Cu-TTP is stronger, compared to the native β-CD, which indicates that the capacity matching plays a crucial role in the inclusion procedure except for the hydrophobic effect. In addition ¹HNMR spectra supports the inclusion conformation of the TM-β-CD-Cu-TTP inclusion complex, indicating the interaction mechanism of inclusion processes.     

Cavity size effect on ICT-dual emission of p-(N,N-dimethylamino)-2-styrylquinoline: complexation with cyclodextrin derivatives

The effect of cyclodextrin inclusion complex formation on the intramolecular charge transfer (ICT) of the included 4-N,N-dimethylamino-2-strylquinoline (2-StQ-NMe₂) has been studied in detail. 2-StQ-NMe₂ in presence of α-, β-, γ- and HP-α- and Hp-β-CDs predominantly exhibits ICT fluorescence predominantly than the emission from locally excited state, whereas in presence of HP-γ-CD the later is observed. In presence of α-CD, 2:1 complexation of the 2-StQ-NMe₂ is observed in addition to 1:1 complexation. The observed results are explained by the CD cavity size and an active role for the secondary hydroxyl groups present in the wider rim of the CD cavity and also which finds support from absorption, emission, lifetime and molecular modeling studies. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

FÖRSTER TRANSFER CALCULATIONS BASED ON CRYSTAL STRUCTURE DATA FROM Agmenellum quadruplicatum C-PHYCOCYANIN

Excitation energy transfer in C-phycocyanin is modeled using the Forster inductive resonance mechanism. Detailed calculations are carried out using coordinates and orientations of the chromophores derived from X-ray crystallographic studies of C-phycocyanin from two different species (Schirmer et al, J. Mol. Biol. 184 , 257–277 (1985) and ibid. , 188 , 651-677 (1986)). Spectral overlap integrals are estimated from absorption and fluorescence spectra of C-phycocyanin of Mastigocladus laminosus and its separated subunits. Calculations are carried out for the β-subunit, αβ-monomer, (αβ)₃-trimer and (αβ)₀-hexamer species with the following chromophore assignments: β155 = 's'(sensitizer), β84 ='f (fluorescer) and α84 ='m'(intermediate):]:. The calculations show that excitation transfer relaxation occurs to 3=98% within 200 ps in nearly every case; however, the rates increase as much as 10-fold for the higher aggregates. Comparison with experimental data on fluorescence decay and depolarization kinetics from the literature shows qualitative agreement with these calculations. We conclude that Forster transfer is sufficient to account for all of the observed fluorescence properties of C-phycocyanin in aggregation states up to the hexamer and in the absence of linker polypeptides.     

Spectroscopic properties,structure, and photoinduced motion of 4-(2-naphthyl)pyridine in cyclodextrin cavities

Spontaneous and photoinduced protonation of 4-(2-naphthyl)pyridine (1) in solutions and in complexes with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was studied using the absorption and fluorescence spectroscopies. The structures and stabilities of complexes of compound 1 and its quaternized derivative, 1-methyl-4-(2-naphthyl)pyridinium perchlorate (3), with β-CD and HP-β-CD were examined by ¹H NMR titration (logK = 1.5–2.3). The molecule of naphthylpyridine 1 is always in the cyclodextrin cavity, regardless of the pH value of the solution. 2-Hydroxypropyl-β-cyclodextrin binds better the neutral form of compound 1 than does β-CD, while naphthylpyridinium salts exhibit nearly equal affinities to both cavitands. According to spectroscopic data, pK _a (1) is 5.12 in water, which favors protonation of the N atom both in the ground and excited states; as a result, the fluorescence spectrum exhibits only the band of the protonated form with a lifetime of 15 ns. The addition of HP-β-CD to a solution of naphthylpyridine 1 results in the formation of inclusion complex 1@HP-β-CD, lowers pK _a to 4.62, and gives rise to a fluorescence band of the nonprotonated form of compound 1 with a lifetime of 1.25 ns. Therefore, the presence of compound 1 in the HP-β-CD cavity precludes its protonation in the excited state. The initial portions of the fluorescence curves for compound 1 in solution and in its complex with HP-β-CD obtained upon pulsed excitation were compared to propose the initiation mechanism of short-lived fluorescence of the nonprotonated form of naphthylpyridine 1. Quantum chemical modeling of the protonation and complexation of compound 1 in the presence of water was performed. Based on the results obtained, a reversible photoinduced mechanical motion of naphthylpyridine 1 in the HP-β-CD cavity was suggested.     

TEMPERATURE DEPENDENCE OF PICOSECOND FLUORESCENCE KINETICS OF A CYANOBACTERIAL PHOTOSYSTEM I PARTICLE*

Picosecond time-resolved fluorescence of photosystem I particles isolated from Synechococcus sp. was recorded in the wavelength range from 680 nm to 736 nm for temperatures of 6°C to 42°C and - 100°C using the single-photon-timing technique. By global analysis of the data we found four contributing lifetime components at the higher temperatures (T₁ ' 12 ps, T₁= 35 ps, T₃ ' 65 ps, T₄ ' 1000 ps). We attribute T₁ to an energy transfer between two pigment pools, T₂ to the charge separation process in the reaction center, component T₃ is assigned to aggregate and T₄ to uncoupled chlorophyll emission. The corresponding decay-associated spectra are presented. We also applied a target analysis procedure to fit parameters of a kinetic model directly to the data. The resulting rate constants and species-associated spectra are discussed. The data indicate substantial spectral heterogeneity in the antenna with at least three substantially different chlorophyll pools. The overall exciton decay kinetics (by charge separation) is trap-limited.     

Photoinduced intramolecular electron transfer of fluorescein and violgen, carbazole

A series of polyads consisting of covalently-(CH2)4-linked fluorescein with carbazole and violger.Live been synthesized and characterized The studies of absorption,emission spectra and fluorescence lifetime quenching indicated that the intramolecular fluorescence quenching of fluorescein by violgen is mainly a static process through the formation of non emission complex (fluorescence quenching efficiency φQ=0.97,lifetime quenching efficiency φH 0,quenching efficiency of formation of non-emission complex φC=0.97); while the quenching by carbazole is mainly a dynamic electron transfer process (φQ=0.63,φET=0.63,φC=0).In the violgen-fluorescein-carbazole triads,φQ=0.97,Q ET=0.65,φC=0.32,which suggests that the photoinduced interaction of fluorescein-carbazole pair and that of violgen-fluorescein pair are in a competitive process,the dynamic electron transfer from carbazole to fluorecein is dominant in the process The free energy change of the photoinduced electron transfer and the back reac-tiorns i     

Hidden Relaxation Channels in Aqueous Methylene Blue after Functionalization of Graphene Oxide Probed by Transient Absorption Spectroscopy

The mixture of graphene oxide (GO) and dye molecules may provide some new applications due to unique electronic, optical, and structural properties. Methylene blue (MB), a typical anionic dye, can attach on GO via π-π stacking and electrostatic interaction, and the molecule removal process on GO has been observed. However, it remains unclear about the ultrafast carrier dynamics and the internal energy transfer pathways of the system which is composed of GO and MB. We have employed ultrafast optical pump-probe spectroscopy to investigate the excited dynamics of the GO-MB system dispersed in water by exciting the samples at 400 nm pump pulse. The pristine MB and GO dynamics are also analyzed in t_andem for a direct comparison. Utilizing the global analysis to fit the measured signal via a sequential model, five lifetimes are acquired:(0.61±0.01) ps, (3.52±0.04) ps, (14.1±0.3) ps, (84±2) ps, and (3.66±0.08) ns. The ultrafast dynamics corresponding to these lifetimes was analyzed and the new relaxation processes were found in the GO-MB system, compared with the pristine MB. The results reveal that the functionalization of GO can alter the known decay pathways of MB via the energy transfer from GO to MB in system, the increased intermediate state, and the promoted energy transfer from triplet state MB to ground state oxygen molecules dissolved in aqueous sample.     

Clarifying and illustrating the electronic energy transfer pathways in trimeric and hexameric aggregation state of cyanobacteria allophycocyanin within the framework of Förster theory

Within the framework of the Förster theory, the electronic excitation energy transfer pathways in the cyanobacteria allophycocyanin (APC) trimer and hexamer were studied. The associated physical quantities (i.e., excitation energy, oscillator strength, and transition dipole moments) of the phycocyanobilins (PCBs) located in APC were calculated at time‐dependent density functional theory (TDDFT) level of theory. To estimate the influence of protein environment on the preceding calculated physical quantities, the long‐range interactions were approximately considered with the polarizable continuum model at the TDDFT level of theory, and the short‐range interaction caused by surrounding aspartate residue of PCBs were taken into account as well. The shortest energy transfer time calculated in the framework of the Förster model at TDDFT/B3LYP/6–31+G* level of theory are about 0.10 ps in the APC trimer and about 170 ps in the APC monomer, which are in qualitative agreement with the experimental finding that a very fast lifetime of 0.43–0.44 ps in APC trimers, whereas its monomers lacked any corresponding lifetime. These results suggest that the lifetime of 0.43–0.44 ps in the APC trimers determined by Sharkov et al. was most likely attributed to the energy transfer of α¹‐84 ? β³‐84 (0.23 ps), β¹‐84 ? α²‐84 (0.11 ps) or β²‐84 ? α³‐84 (0.10 ps). So far, no experimental or theoretical energy transfer rates between two APC trimmers were reported, our calculations predict that the predominate energy transfer pathway between APC trimers is likely to occur from α³‐84 in one trimer to α⁵‐84 in an adjacent trimer with a rate of 32.51 ps. © 2014 Wiley Periodicals, Inc.     

Photoinduced intramolecular electron transfer between fluorescein and carbazole

Several dyads consisting of a fluoreseein covalently linked with a carhazole at site 2 or site 6 have been synthesized and characterized.Studies of absorption spectra,emission spectra and fluorescence lifetime quern hing Indicate that the ground-state interaction between fluorescein and carhazole in dyads is negligible and the intramolecular electron transfer (ET) reactions are mainly of dynamic process.Moreover,the efficiency and raie conslam of lectron transfer reactions in ZFO4 (carbazole linked at site 2'of fluorescein) are larg er than those in 4FOZ (carbazole linked at site 6 of fluorescein) 0 74; KET 11×108S-1),because the mutual orientation of donor and acceptor in ZFO4 is nearly face-to-face,which is more favorable to the process than the shoulder-to-shoulder mutual orientation in 4FOZ.Estimations are also formed of the free energy change of the photomduced electron transfer and the back reactions in the dyads.     

(He 1) photoelectron spectra of vinyl- and (1-dimethylaminovinyl)pyridines

The (He 1) photoelectron spectra of -, -, -vinyl, -, -, and -(1-dimethylvinyl)-pyridines, 1-dimethyl- and 1-diethylaminostyrenes were obtained and interpreted within the framework of the molecular orbital perturbation theory. In both pyridine derivative series, there is a regular increase in the ionization energy of the 1a ₂, C=C and n_en orbitals and decrease in the ionization energy of the 2b₁ orbitals in the order < < (inversion of orbitals 1a ₂ and 2b₁ is found for -vinylpyridine). The splitting of the energy levels of the heterocycle in dimethylaminovinylpyridines is less than in the corresponding vinyl derivatives, which indicates a weakening of the interaction between the aromatic (or heteroaromatic) ring and the enamine fragment extruding from the ring plane. The ionization energy of the unshared electron pair of the nitrogen atom of the pyridine ring for all the compounds except for -(1-dimethylaminovinyl)pyridine (which displays an ortho effect) is close to that for pyridine. The photoelectron spectral data are compared with the MO energies calculated by the MINDO/3 method.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 103–108, January, 1985.     

ENERGY TRANSFER AMONG THE CHROMOPHORES OF C-PHYCOCYANIN FROM Anabaena variabilis USING STEADY STATE AND TIME-RESOLVED FLUORESCENCE SPECTROSCOPY

Abstract We have investigated the model of energy transfer between sensitizing (s) and fluorescing (f) chromophores for the αβ monomer and for the separated α and β subunits of C-phycocyanin from Anabaena variabilis using fluorescence emission spectroscopy, fluorescence excitation polarization, and picosecond-resolved fluorescence decay kinetics. The fluorescence emission maximum occurs at 640 nm for all samples. The fluorescence excitation polarization is constant ( P = 0.40) across the absorption hand for the α subunit, but it increases across the absorption band towards longer wavelength for the β subunit and the αβ monomer. The fluorescence decay kinetics exhibit two exponential lifetimes of 1.3-1.5 ns and 340-500 ps for the αβ monomer and for the α and β subunit preparations.
We attribute the change in polarization across the absorption band to energy transfer among the three chromophores in the αβ monomer and among the two chromophores in the separated β subunit. The constant, relatively high polarization in the separated a subunit, having only one chromophore, is consistent with the absence of both energy transfer and chromophore rotation. The concentration of the α subunit did not affect the decay kinetics, suggesting that the short lifetime component does not arise from aggregation of the α subunits. The biexponential decay kinetics of the α subunit cannot be explained using the sensitizing-fluorescing model. The possibility of conformational interactions is under investigation.     

COMPUTER SIMULATION OF EXCITON JUMPING STATISTICS AND ENERGY FLOW IN C-PHYCOCYANIN OF ALGAE Agmenellum quadruplicatum IN THE PRESENCE OF TRAPS

Abstract—Energy migration has been studied in C-phycocyanin (C-PC) rods with traps located in the terminal trimer disc, using the Monte Carlo method and the system of differential equations. It has been found that jump time statistics can be described by the function F = C(t/0>)exp(-t/ < t_o>), where C is the constant, t and < t₀ > are, respectively, the exciton jump time and its averaged value for chromophores of the corresponding spectral types (α 84 , β84 or β155). The values < t₀ > were calculated for the cases of C-PC monomers, trimers and higher associates.
The C-PC model, which consists of three hexamers with traps located in the β84 chromophores of the peripheral trimer, was examined. It was found that the total efficiency of excitation capturing, ø_tr, exceeds 90%, provided "local" quantum yield of energy trapping ø₀ > 10%. The ø₀ value influences both the excitation lifetime (τ) and the mean number of excitation jumps (N_iump) before its conversion. For the ø₀ = 100% and 10%, the corresponding lifetimes and numbers of jumps were calculated to be τ= 75 and 155 ps and N_jump= 105 and 222 jumps, respectively.
The dynamics of excitation redistribution along the C-PC rods and the fluorescence kinetics for various ø₀ values were calculated for C-PC chromophores excited by a +, and the correlation between these processes and ø ₀ , was disclosed. The transient processes of excitation redistribution were shown to proceed within a time period t < 30 ps.