Picosecond Time-resolved Absorption Research Articles

Stochastic treatment of the dynamics of excitons and excitonic molecules in CuCl nanocrystals.

Dynamics of excitons and excitonic molecules in CuCl nanocrystals were investigated by means of both picosecond time-resolved luminescence and femtosecond transient absorption. Stochastic as well as rate-equation treatments are made to explain the temporal changes of both luminescence and absorption. In the stochastic treatment, a Monte Carlo simulation is made for ${10}^{5}$ nanocrystals with the initial condition that the exciton number distribution follows the Poisson distribution. The stochastic treatment satisfactorily explains all the experimental results, while the rate-equation treatment does not. Success of the stochastic treatment shows the unique property of the dynamics of excitons and excitonic molecules in quantum dots arising from discreteness of the exciton number. \textcopyright{} 1996 The American Physical Society.

Linkage and Solvent Dependence of Photoinduced Electron Transfer in Zincporphyrin-C60 Dyads

Four different kinds of C60-linked zincporphyrins have been prepared by changing systematically the linking position at meso-phenyl ring from ortho to para and their photophysical properties have been investigated. Regardless of the linkage between the two chromophores, photoinduced charge separation (CS) and subsequent charge recombination (CR) were observed in a series of zincporphyrin-C60 dyads by picosecond fluorescence lifetime measurements and time-resolved transient absorption spectroscopy. In THF the CS occurs from both the excited singlet state of the porphyrin and the C60 moieties, implying that the increase of the absorption cross section by both the chromophores results in the efficient formation of the ion pair (IP) state. On the other hand, in benzene the IP state generated by the photoinduced CS from the excited singlet state of the porphyrin to the C60 produces or energetically equilibrates with the locally excited singlet state of the C60. Both the CS and CR rates for the meta isomer are ...

Excited States of Poly(3-octylthiophene) Studied by Picosecond Time-Resolved Absorption Spectroscopy Using a Streak Camera

The excited states of π-conjugated poly(3-octylthiophene) were studied by laser flash photolysis technique. The nanosecond time-resolved absorption spectra for poly(3-octylthiophene) showed the triplet−triplet (T−T) absorption band (λmax 800 nm) in the near-IR region. The intersystem crossing process was investigated by picosecond time-resolved absorption spectroscopy. The absorption−time profile obtained by picosecond laser flash photolysis of poly(3-octylthiophene) using a streak camera showed an initial rising component just after the photolysis and a slow growing component within a few nanoseconds. They were assigned to excited singlet and triplet states, respectively. The absorption−time profiles were analyzed by curve-fitting considering the decay of the excited singlet state and the growth of the excited triplet state. The intersystem crossing rate constant from the excited singlet state to the excited triplet state was determined to be 1.54 × 109 s-1 by the curve-fitting. The S1−Sn and T−T absorption bands were depicted separately using the fitting parameters.

Picosecond time-resolved near-IR spectra of C60 excited states by pump-probe measurements using a probe beam based on broad-band optical parametric generation

Picosecond time-resolved absorption spectra of C60 singlet and triplet excited states are observed in the near-IR region in the region 700–1300 nm by the pump-probe technique using a probe beam based on broad-band optical parametric generation (OPG) in β-barium borate (BBO) pumped by a picosecond laser pulse at 532 nm and using an InGaAs multichannel detector.

Photoinduced Electron Transfer from Polygermane to C60 Studied by Laser Flash Photolysis

Electron transfer from poly(phenylmethylgermylene) (PMePhGe) to photoexcited C{sub 60} in benzene-acetonitrile solution has been investigated by 532 nm laser flash photolysis in the near-IR region. The transient absorption band of the C{sub 60} triplet state ({sup 3}C{sub 60}{sup *}) appeared immediately after nanosecond laser exposure. The rate constant of the electron transfer from PMePhGe to {sup 3}C{sub 60}{sup *} was determined to be 2.33 x 10{sup 8} M{sup -1} s{sup -1}, which was similar to that for poly(methylphenylsilylene). Electron transfer from the singlet state of C{sub 60} ({sup 1}C{sub 60}{sup *}) was investigated by fluorescence quenching experiments and the quenching rate constant was determined to be 4.00 x 10{sup 10} M{sup -1} s{sup -1}. The rate constant of intersystem crossing from {sup 1}C{sub 60}{sup *} to {sup 3}C{sub 60}{sup *} was determined to be 1.10 x 10{sup 9} s{sup -1} by picosecond time-resolved absorption spectroscopy using a streak camera. Electron transfer from {sup 1}C{sub 60}{sup *} to PMePhGe and intersystem crossing from {sup 1}C{sub 60}{sup *} to {sup 3}C{sub 60}{sup *} are competitive, and the intersystem crossing is dominant in a dilute solution system. When a 355 nm laser was used as the excitation light, photochemical intermediates were produced frommore » the direct photolysis of PMePhGe in addition to the electron transfer. 36 refs., 9 figs.« less

Picosecond Time-Resolved Absorption Dynamics in the Artificial Bacteriorhodopsin Pigment BR6.9

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPicosecond Time-Resolved Absorption Dynamics in the Artificial Bacteriorhodopsin Pigment BR6.9J. K. Delaney, G. H. Atkinson, M. Sheves, and M. OttolenghiCite this: J. Phys. Chem. 1995, 99, 19, 7801–7805Publication Date (Print):May 1, 1995Publication History Published online1 May 2002Published inissue 1 May 1995https://doi.org/10.1021/j100019a069RIGHTS & PERMISSIONSArticle Views24Altmetric-Citations7LEARN 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 (606 KB) Get e-Alerts

Steady state and time-resolved studies on the redox behaviour of 1,8-naphthalimide in the excited state

The redox behaviour of 1,8-naphthalimide in its first excited singlet state is investigated by steady state and time-resolved studies. Efficient fluorescence quenching of this compound by aromatics and amines is interpreted in terms of a charge transfer mechanism. It is shown that the fluorescence quenching in some cases proceeds through exciplex formation. Weak exciplex emission is seen even in polar solvent such as acetonoitrile. Picosecond time-resolved transient absorption studies enables characterization of S1→Sn absorption of the 1,8-napthalimide compound, and the temporal behaviour of the transient absorption in polar solvents led us to believe that ionic products are exclusively formed from the singlet state. In non-polar solvents, the lack of observation of the ionic products is explained in terms of geminate recombination.

Electron transfer over two porphyrins in linear porphyrin arrays

Using pyromellitimide-linked, linear, 1,4-phenylene-bridged di- or tri-porphyrins, the intramolecular electron-transfer reaction from the singlet excited state of the distal doubly strapped free-base porphyrin to the pyromellitimide acceptor was studied by means of picosecond time-resolved fluorescence and transient absorption spectroscopy. The electron transfer is more effective in magnesium-porphyrin bridged models than in zinc-porphyrin bridged ones. Remarkably, the electron transfer over two porphyrins proceeds with rates almost similar to that of electron transfer over one porphyrin regardless of the bridging metal porphyrin.

Dynamics of excited-state intramolecular proton transfer reactions in piroxicam. Role of triplet states

The picosecond time-resolved fluorescence and transient absorption behavior of piroxicam at room temperature are reported. The keto tautomer in the excited singlet state ( 1K*) formed via the fast intramolecular proton transfer (≈ 20 ps) is observed. The short-lived (7.5 ns) triplet state of keto tauomer ( 3K*) is generated from 1K * in toluene whereas it is hardly observed in ethanol. Consequently, rapid reverse proton transfer takes place from 3K * to the enol triplet state ( 3E *.

Photodissociation of aminophenyldisulfide and aminophenylthiol in the liquid phase. Geminate recombination and the dimer formation of p-aminophenylthiyl radical

Measuring picosecond time-resolved absorption spectra in the visible region, the photodissociation of p-aminophenyldisulfide and p-aminophenylthiol in various solutions has been investigated. In tens of picoseconds delay times a decay of p-aminophenylthiyl radical ascribed to the geminate recombination was observed for p-aminophenyldisulfide in nonpolar solvents, while the decay of the radical was not detected for p-aminophenylthiol in the same time region. In addition to a slight change in the spectral shape of p-aminophenylthiyl radical, the rise of the broad absorption band, which should be assigned to the radical dimer, follows the geminate recombination in nonpolar solvents.

Observation and characterization of excimer emission from anthracene included in NaX zeolite

We observed for the first time an excimer emission of anthracene included in the supercages of zeolite X at high ratios of anthracene to supercage. The mechanism giving rise to the excimer emission was ascribed to charge recombination of anthracene cation—anion radical pair on the basis of picosecond time-resolved diffuse reflectance transient absorption studies as well as picosecond fluorescence measurements.

Steady state and transient absorption spectra of quinhydrones

Picosecond time-resolved absorption spectra of crystalline quinhydrone complexes, excited at the charge transfer (CT) band, were obtained. Transient spectra weakly depend on the excitation wavelength and are similar in shape and frequency to the steady state absorption spectra within the CT band. The positive absorption at 20 000–24 000 cm −1 is assigned to radical ion species. The kinetics of induced absorption depend on the method of preparation of the crystalline complex and can be fitted to a biexponential decay with time components τ 1=130–180 ps and τ 2 > 5000 ps. Luminescence of the complexes in the range 10 000–13 000 cm −1 is observed. Its delay time increases from 300 to 1000 ps with decreasing probing frequency. Quantum chemical calculations of the absorption spectra of the complexes and intermediate radical species were carried out.

Hot carrier excitation of adlayers: Time-resolved measurement of adsorbate-lattice coupling.

Picosecond time-resolved infrared absorption measurements of CO/Cu(100) following visible and ultraviolet laser pumping allow a determination of the time scales for photoexcited carriers and lattice phonons to couple to the CO frustrated translation vibrational mode.

Determination of rates of hole transfer from free-base porphyrin to zinc porphyrin across aromatic spacers

Picosecond excited-state dynamics of conformationally constrained triads 1– 4, zinc porphyrin (ZnP)-free-base porphyrin (H 2P)-1,4:5,8-naphthalenetetracarboximide (NIm) bearing aromatic spacers between the ZnP and H 2P moieties, were studied by picosecond time-resolved transient absorption spectroscopy. Upon photo-excitation in THF, these triads provide long-lived ion pair states (ZnP) +-H 2P-(NIm) − via charge separation between the 1(H 2P) * and NIm followed by a hole-transfer reaction from the (H 2P) + to the ZnP. Rates of this hole transfer, being crucial parameters in determining quantum yields for formation of long-lived ion pair states, were determined. The hole transfer does not occur in less polar benzene solution.

Anomalous Lifetime Shortening of S1 trans-Stilbene in Carbon Tetrachloride as Revealed by Picosecond Time-resolved Raman, Absorption, and Fluorescence Spectroscopies

Abstract The lifetime of the first excited singlet state of trans-stilbene (S1 tSB) in carbon tetrachloride at room temperature is determined to be 3.1 ± 0.2 ps with the use of time-resolved Raman, absorption, and fluorescence spectroscopies. The lifetime of 3.1 ps is shorter than the shortest value ever reported by an order of magnitude. The steady state photoirradiation of tSB in carbon tetrachloride shows that the decomposition of the tSB molecule is the primary cause of the lifetime shortening.

Early excited state dynamics of pentacarbonyl(4-cyanopyridine)tungsten and pentacarbonyl(4-formylpyridine)tungsten: observation of an ultrafast intersystem crossing

Picosecond time-resolved absorption spectra of W(CO) 5 (4-cyanopyridine) and W(CO) 5 (4-formylpyridine) complexes were measured following excitation into the ligand-field, LF (355 nm), and, for the latter complex, also into the metal to ligand charge-transfer, MLCT (532 nm), absorption bands. In each case, formation of the transient absorption spectrum of the long-lived 3 MLCT excited state was observed. Its population follows biphasic kinetics

Picosecond time-resolved absorption and fluorescence dynamics in the artificial bacteriorhodopsin pigment BR6.11

The picosecond molecular dynamics in an artificial bacteriorhodopsin (BR) pigment containing a structurally modified all-trans retinal chromphore with a six-membered ring bridging the C11=C12-C13 positions (BR6.11) are measured by picosecond transient absorption and picosecond time-resolved fluorescence spectroscopy. Time-dependent intensity and spectral changes in absorption in the 570-650-nm region are monitored for delays as long as 5 ns after the 7-ps, 573-nm excitation of BR6.11. Two intermediates, J6.11 and K6.11/1, both with enhanced absorption to the red (> 600 nm) of the BR6.11 spectrum are observed within approximately 50 ps. The J6.11 intermediate decays with a time constant of 12 +/- 3 ps to form K6.11/1. The K6.11/1 intermediate decays with an approximately 100-ps time constant to form a third intermediate, K6.11/2, which is observed through diminished 650-nm absorption (relative to that of K6.11/1). No other transient absorption changes are found during the remainder of the initial 5-ns period of the BR6.11 photoreaction. Fluorescence in the 650-900-nm region is observed from BR6.11, K6.11/1, and K6.11/2, but no emission assignable to J6.11 is found. The BR6.11 fluroescence spectrum has a approximately 725-nm maximum which is blue-shifted by approximately 15 nm relative to that of native BR-570 and is 4.2 +/- 1.5 times larger in intensity (same sample optical density). No differences in the profile of the fluorescence spectra of BR6.11 and the intermediates K6.11/1 and K6.11/2 are observed. Following ground-state depletion of the BR6.11 population, the time-resolved fluroescence intensity monitored at 725 nm increases with two time constants, 12 +/- 3 and approximately 100 ps, both of which correlate well with changes in the picosecond transient absorption data. The resonance Raman spectrum of ground-state BR6.11, measured with low-energy, 560-nm excitation, is significantly different from the spectrum of native BR-570, thus confirming that the picosecond transient absorption and picosecond time resolved fluorescence data are assignable to BR6.11 and its photoreaction alone and not to BR-570 reformed during there constitution process (<5% of the BR6.11 sample could be attributed to native BR-570).The J6.11 and K6.11 absorption and fluorescence data presented here are generally analogous to those measured for native J-625 and K-590, respectively, and therefore, the primary events in the BR6.11 photoreaction can be correlated with those in the native BR photocycle. The BR6.11 photoreaction, however, exhibits important differences including slower formation rates for J and K intermediates as well as the presence of a second K intermediate. These results demonstrate that the restricted motion in the C11=C12-C13 region of retinal found in BR6.11 does not greatly change the overall photoreaction mechanism,but does alter the rates at which processes occur.

Picosecond events in the phototransformation of phytochrome — a time-resolved absorption study

Picosecond time-resolved transient absorption studies with phytochrome in its red light absorbing form (P r) isolated from rye ( Secale cereale cv. Danae) are reported. After excitation of P r with 6 ps pulses at 621 nm the transient absorption spectra were measured at various delay times from 5 ps up to 1 ns. Upon excitation an increase in the transient absorption around 400 nm immediately appeared, which is ascribed to the first excited state absorption of P r. With a delay of about 15 ps a strong bleaching of the P r ground state absorption around 665 nm emerged. After a series of further absorption changes, an increase in absorbance occurred above 685 nm. Since this transient absorption persisted over the 1 ns time-window measured, it is interpreted as being due to the formation of lumi-R. Based on the time evolution of the observed absorption changes it seems likely that two pools of lumi-R were formed. In addition, it was found from the kinetics of the picosecond absorption changes that the relaxation of excited P r obviously involves processes which follow a non-exponential rate law. From a comparison with picosecond adsorption spectroscopy on deuterated P r and a 39 kDa chromopeptide, conclusions about the first relaxation steps in the phototransformation of P r are drawn. It is suggested that they involve rotations at the single bonds in the chromophoric methine bridges.

Geometry- and solvent-polarity-dependent photoinduced electron transfer in conformationally restricted magnesium—free-base hybrid diporphyrins

Excited-state dynamics of a series of conformationally restricted magnesium—free-base hybrid diporphyrins (MgPH 2P) have been studied by fluorescence lifetime measurement and picosecond time-resolved transient absorption spectroscopy. Upon photoexcitation in toluene and THF, intramolecular singlet-singlet energy transfer from the 1(MgP)* to the H 2P has been observed regardless of the spacer between the two subunits and the 1(H 2P)* thus formed decays with the same time constant with the reference monomeric H 2P in each solvent. In DMF, the photoexcited state dynamics of MgPH 2P depends on the geometry of the models; charge separated state (MgP) +—(H 2P) − is generated from both of the 1(MgP)* and 1(H 2P)* in hybrid diporphyrins with shorter separation, while only the singlet—singlet energy transfer from the 1(MgP)* to the H 2P has been observed for models with larger separations.

Charge-transfer complexes of discogenic molecules : a time-resolved study based on Kerr ellipsometry

Charge-transfer complexes formed by a discogenic electron donor (2,3,6,7,10,11-hexa-n-pentyloxytriphenylene) and a non-discogenic electron acceptor (2,4,7-trinitrofluoren-9-one) in non-polar solvents are studied by picosecond time-resolved absorption spectroscopy based on Kerr ellipsometry. The transient spectra obtained following laser excitation either in the charge-transfer band or in the lower lying local acceptor band correspond to the oxidized donor and reduced acceptor. Recombination of the geminate ion pair occurs with a first order rate constant of 1.7 × 1010 s–1. It is shown that the polarization of the transient species absorption is orthogonal to the charge-transfer transition. It is also demonstrated that the relative orientation between the donor and the acceptor in the geminate ion pair is not random.