Picosecond Time-resolved Absorption Research Articles

Energy transfer and primary charge separation in Heliobacterium chlorum studied by picosecond time-resolved transient absorption spectroscopy

Transfer of excitation energy to the reaction center and photo-oxidation of the primary electron donor, P798, were studied in membranes of Heliobacterium chlorum with a time-resolution of 10 ps or less. The absorption difference spectrum of excited antenna pigments was dominated by a bleaching around 805 nm and analysis of the kinetics showed that the life-time of excited antenna BChl g was essentially equal (about 20 ps) for all three spectral BChl g species, BChl g 778, BChl g 793 and BChl g 808. This indicates that the excitation energy rapidly equilibrates within the antenna and that most of the excitations have accumulated on BChl g 808 within a few ps after excitation. The 20-ps decay is attributed to energy transfer to the reaction center. After 100 ps, the excited BChl g had dissappeared and the remaining absorption difference signal showed a bleaching maximum at 798 nm, caused by the oxidation of the primary electron donor, P798. The rate of decay of antenna excited states was somewhat faster in the presence of P798 + than with reduced reaction centers, which is in agreement with earlier measurements that showed that P798 + is an efficient quencher of fluorescence (Deinum, G., Kramer, H., Kleinherenbrink, F.A.M., Aartsma, T.J. and Amesz, J. (1991) Biochim. Biophys. Acta 1058, 339–344). The time-resolved absorption difference spectrum also showed a bleaching around 670 nm, due to reduction of the primary electron acceptor, A o, which was induced upon excitation at 585 nm, as well as in the Q y-band of antenna BChl g. From the kinetics at 670 nm, we conclude that the reduction of A o occurs at essentially the same rate as the decay of antenna excitations, indicating that charge-separation is a very rapid process.

Dynamics of charge transfer in the excited amine complexes of the fullerenes C 60 and C 70. : A picosecond laser flash photolysis study

In benzene solution, C60 and C70 interact weakly in the ground state with amines having favourable oxidation potentials. Picosecond time-resolved absorption measurements show that on photoexcilation, the weak complexes undergo charge separation to produce ion pairs which in turn undergo fast geminate recombination either to produce the triplet state of the fullerenes or give back the ground slate of the complex, depending on the oxidation potential of the amine. Free-ion yield is generally negligible.

Picosecond time-resolved absorption spectrum measurements of the higher excited singlet state of diphenylacetylene in the solution phase

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPicosecond time-resolved absorption spectrum measurements of the higher excited singlet state of diphenylacetylene in the solution phaseYoshinori Hirata, Tadashi Okada, Noboru Mataga, and Tateo NomotoCite this: J. Phys. Chem. 1992, 96, 16, 6559–6563Publication Date (Print):August 1, 1992Publication History Published online1 May 2002Published inissue 1 August 1992https://doi.org/10.1021/j100195a011RIGHTS & PERMISSIONSArticle Views472Altmetric-Citations90LEARN 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 (588 KB) Get e-Alerts

Laser spectroscopy and photochemistry in micrometre small volumes

The importance of micrometre dimensions in photochemistry is considered, and a systematic study on laser spectroscopy and photochemistry in small micrometre volumes is reported. To measure chemical reactions in the small volumes, submicrometre space- and picosecond time-resolved fluorescence and transient absorption spectroscopy was developed by employing a confocal laser scanning microscope. Laser-trapping phenomena were used for choosing small (micrometre-sized) materials as well as reagents, transferring them to a certain position with micrometre resolution and inducing chemical reactions. Combined with spectroscopic analysis, the laser-trapping technique was developed as a laser manipulation—spectroscopy—reaction method. Utilizing these methods, characteristic micrometre-sized effects were confirmed in the excimer dynamics in microdroplets and photoresponse of gels. Some small (micrometre-sized) reaction fields, which are crucial for conducting chemical reactions, were created by microfabrication techniques. Summarizing our trials, our goal to create an integrated chemical system named microphotoconversion is presented.

Interligand electron transfer and transition state dynamics in Ru(II)trisbipyridine

The interligand electron transfer (ILET) dynamics in the excited metal-to-ligand charge transfer state of RuIItrisbipyridine have been studied using picosecond time-resolved absorption polarization spectroscopy. The ILET dynamics have been studied in several solvents with widely varying relaxation times, and over the temperature range of −85 °C to room temperature. The solvents studied include acetonitrile, propanol, ethylene glycol, and glycerol. The results show that ILET is relatively fast in acetonitrile (∼47 ps), slower and nonexponential in propanol and ethylene glycol (∼30–200 ps), and fast in glycerol (∼30 ps). The glycerol results are roughly temperature independent. These results can be understood in terms of a model in which photoexcitation places the system near the ILET transition state and solvent relaxation competes with ILET in the nascent distribution. Following solvent relaxation a slower, steady state (probably transition state theory) rate is obtained.

Vibrational energy dissipation process in solution: picosecond laser photolysis studies of biphenylene

Biphenylene in various solvents is investigated by picosecond time-resolved absorption spectroscopy. The time dependence of the spectral shape of the vibrationally hot S n ←S 1 absorption was analyzed by using the Urbach relation. Vibrational energy flow to the solvent molecules in the surroundings from the higher vibrational state of S 1 was proportional to the excess vibrational energy.

Picosecond spectroscopy of dihydro biliverdin

Picosecond time-resolved fluorescence and absorption spectroscopy was performed on dihydro biliverdin, a model for the chromophore in the plant pigment phytochrome, a chromoprotein governing plant growth. Close agreement between the model compound and the native chromophore proves the importance of the saturated pyrrol ring for the decay kinetics and renders chromophore protonation in phytochrome unlikely.

Intramolecular photoinduced electron transfer in fixed distance triads consisting of free-base porphyrin, zinc porphyrin, and electron acceptor

Intramolecular photoinduced electron transfer reaction of a series of fixed distance triads consisting of free-base porphyrin, zinc porphyrin, and quinone or pyromellitimide have been investigated by means of steady-state fluorescence spectroscopy, picosecond time-resolved fluorescence spectroscopy, and picosecond time-resolved transient absorption spectroscopy. The singlet excited state of the distal free-base porphyrin was found to be quenched by the attached electron acceptor at 298 K in THF and at 77 K in EPA, indicating long distance electron transfer from the free-base porphyrin to the acceptor. However, long-lived charge separated states were not formed in these model compounds.

Steady state and time-resolved spectroscopic studies of α- and β-naphthanilides

Using chemical substitution and polarity perturbation effects, three competitive fluorescence emissions from a common initial excited singlet state of α and β-naphthanilide are observed in non-polar solvents at 298 K. The fluorescence emissions are assigned as the normal fluorescence from a locally excited state (S 1(LE) → S 0), the proton-transfer tautomer emission (S′ 1(PT) → S′ 0(PT)) and the intramolecular charge-transfer fluorescence (S″ 1(TICT) → S 0(FC)). The picosecond time-resolved absorption spectra confirm the presence of excited species in different electronic states, e.g. S 1(LE) and S′ 1(PT) with comparable decay constants and S″ 1(TICT) and T 1(LE) with larger decay constants. At 77 K, the luminescence spectra appear as normal fluorescence (for N-methyl-α-naphthanilide and N-methyl-β-naphthanilide) or a fluorescence emission from microcrystals (for α- and β-naphthanilide) and very strong phosphorescence emission.

Photoinduced electron transfer reactions in quinone-linked zinc porphyrin arrays

Intramolecular photoinduced electron transfer reactions of conformationally restricted quinone-linked zinc porphyrin monomer, dimer, and trimers have been studied by picosecond time-resolved absorption spectroscopy. Both charge separation and charge recombination are very rapid in the monomeric model, while charge recombination is partly impeded in the dimeric model. In the trimeric models, the singlet excited state of the distal coplanar diporphyrin is efficiently quenched by the attached quinone and long-lived charged separated states are formed most probably by electron transfer from the diporphyrin part to the monomeric porphyrin part competing with rapid charge recombination reaction.

Picosecond time-resolved absorption and fluorescence in the bacteriorhodopsin photocycle: Vibrationally-excited species

A rate-equation model quantitatively describing the changes in the ground and excited electronic-state properties of the retinal chromophore during the initial 100 ps of the room temperature bacteriorhodopsin (BR) photocycle is presented. The model is derived from both picosecond time-resolved absorption and fluorescence measurements made using a pump-probe laser configuration (2,3-6 ps pulses operating over the 565–650 nm range). A direct, quantitative correlation between the absorption and fluorescence signals is based on their sequential measurement from the same sample and under the same experimental conditions. Two new aspects of the room-temperature BR photocycle are evident from these results: (i) the rate-equation model derived from transient absorption data alone does not quantitatively simulate the time-dependent fluorescence and (ii) the inclusion in the model of vibrationally excited, ground-state species (e.g., vibrationally excited BR (BR′) formed during optical pumping and vibrationally excited K (K′) populated during the photocycle decay of J) provide excellent simulations of both transient absorption and fluorescence data.

Femtosecond-picosecond laser photolysis studies on the dynamics of excited charge-transfer complexes: aromatic hydrocarbon-acid anhydride, -tetracyanoethylene, and -tetracyanoquinodimethane systems in acetonitrile solutions

Formation processes of contact ion pairs (CIP) from the excited Franck-Condon (FC) state of charge-transfer (CT) complexes of aromatic hydrocarbons with acid anhydride as well as cyano compound acceptors in acetonitrile solution and charge recombination (CR) rates (k{sub CR}{sup CIP}) of produced CIP states have been investigated by femtosecond and picosecond laser phototlysis and time-resolved absorption spectral measurements covering a wide range of free energy gap-{Delta}G{degree}{sub ip} between the ion pair and the ground state. It has been confirmed that the CIP formation becomes faster and k{sub CR}{sup CIP} of the produced CIP increases with increase of the strengths of the electron donor (D) and acceptor (A) in the complex, i.e., with decrease of the {minus}{Delta}G{degree}{sub ip} value. This peculiar energy gap dependence of k{sub CR}{sup CIP}, quite different from the bell-shaped one observed in the case of the solvent-separated ion pairs (SSIP) or loose ion pairs (LIP) formed by encounter between fluorescer and quencher in the fluoresence quenching reaction, has been interpreted by assuming the change of electronic and geometrical structures of CIP depending on the strengths of D and A.

Picosecond transient absorption spectra and kinetics of salicylidenaniline

Using the picosecond time-resolved absorption spectroscopic technique, the transient absorption spectra of salicylidenamline have been investigated and the room-temperature kinetic data are presented. A possible mechanism of the formation of the photochromic products of salicylidenamlme is proposed.

Picosecond time-resolved absorption and emission studies of pyrazolotriazole azomethine dyes

The temperature- and viscosity-dependent photochemistry of three pyrazolotriazole azomethine dyes, which can undergo syn–anti isomerisation, has been studied using ps absorption, single photon counting (SPC) and steady-state emission techniques. Emission intensities are viscosity dependent, with ϕF increasing from ca. 0.005 to ca. 1 in di-n-butylphthalate as the glass-transition temperature is approached. SPC fluorescence decay kinetics are non-monoexponential for all dyes both in rigid organic glasses at 77 K and in solution. Reasonable fits to two exponentials can be obtained with a dominant (ca. 80–90%) decay process of τ≈ 4 ns and a secondary component of τ≈ 1 ns at 77 K in rigid glasses. At 297 K in 96 : 4 glycerol–ethanol the dominant fluorescence decay process (ca. 75%) has τ⩽ 10 ps, and there is a secondary component with τ≈ 60 ps. Picosecond transient absorption studies show three transient states. One is assigned to a fluorescent state because of a stimulated emission band; the lifetime is viscosity dependent with τ 60 ps in glycerol–ethanol (96 : 4) at 4 °C, but only ca. 2 ps at 297 K. A second transient is associated with strong bleaching at the dye absorption maximum, an increase in absorption in the blue spectral region, and τ≈ 6 ps; this is tentatively assigned to a twisted excited singlet state. The third state with τ≈ 3 ps is associated with a weak bleaching at the dye absorption maximum and an absorption increase above ca. 630 nm; this is tentatively assigned to a twisted ground state which relaxes to the syn- and anti-ground-state conformations. A comparison of kinetic and steady-state data suggests partitioning between a highly emitting and zero-emitting state within a few ps of excitation. This is supported by ps absorption studies which show the simultaneous formation of both the fluorescent state and the transient assigned to the twisted excited state within the laser pulse.

ChemInform Abstract: Picosecond Time‐Resolved Absorption and Emission Studies of the Singlet Excited States of Acenaphthylene

Radiative and nonradiative processes in acenaphthylene have been examined by a combination of steady-state and picosecond time-resolved emission and transient absorption measurements. Fluorescence from a higher excited state (S{sub 2}) is found to compete with the nonradiative decay of this state. A lifetime of <40 ps is suggested for the S{sub 2} state. The major deactivation pathway of the S{sub 1} state is identified as an efficient S{sub 1} {yields} S{sub 0} internal conversion. While internal conversion accounts for most of the deactivation of the S{sub 1} state, fluorescence with a very low quantum yield is observed. Transient absorption on the picosecond time scale is assigned to S{sub 1} {yields} S{sub n} absorption. The spectra recorded immediately after excitation are found to have a contribution from vibrationally unrelaxed molecules. A rough estimate for the vibrational relaxation rate is also made.

Photophysics of 7-diethylamino-4-methylcoumarin: picosecond time-resolved absorption and amplified emission study

Picosecond time-resolved pump-probe excited state absorption measurements (with a 400–700 nm window) were used to investigate the conformationally sensitive excited charge transfer state of the 7-diethylamino-4-methylcoumarin ( C1) laser dye in moderately polar to polar solvents. Time-dependent spectral changes due to amplified (probe beam) emission (AE) were observed in the short wavelength region of our window, together with excited state absorption (ESA) at longer wavelengths. These time-dependent changes are consistent with a single excited state species. Since the transient ESA spectrum of C1 is similar to that of the “rigid” C102 aminocoumarin in aqueous solution and to that of C1 in less polar solvents, the transient is assigned to an excited internal charge transfer (ICT) state rather than to a twisted internal charge transfer (TICT) state of C1. These results do not appear to support previous evidence for the formation of a TICT—solvent exciplex in moderately polar to polar solvents.

Picosecond time-resolved absorption and emission studies of the singlet excited states of acenaphthylene

Radiative and nonradiative processes in acenaphthylene have been examined by a combination of steady-state and picosecond time-resolved emission and transient absorption measurements. Fluorescence from a higher excited state (S{sub 2}) is found to compete with the nonradiative decay of this state. A lifetime of <40 ps is suggested for the S{sub 2} state. The major deactivation pathway of the S{sub 1} state is identified as an efficient S{sub 1} {yields} S{sub 0} internal conversion. While internal conversion accounts for most of the deactivation of the S{sub 1} state, fluorescence with a very low quantum yield is observed. Transient absorption on the picosecond time scale is assigned to S{sub 1} {yields} S{sub n} absorption. The spectra recorded immediately after excitation are found to have a contribution from vibrationally unrelaxed molecules. A rough estimate for the vibrational relaxation rate is also made.

Spirooxazine photochromism: picosecond time-resolved Raman and absorption spectroscopy

Photochromatic reactions in three spirooxazine compounds based on the formation of merocyanine isomers are examined by picosecond time-resolved resonance Raman and absorption spectroscopies. Each spirooxazine is excited with 287 nm dye laser pulses (35 ps fwhm) while resonance Raman scattering from the merocyanine isomer(s) formed by ring opening is generated with 575 nm laser excitation into the resultant delocalized, π-electron absorption system. Vibrational resonance Raman spectra of the merocyanine isomer(s) recorded over the 50 ps-1.5 ns interval do not change, indicating that both ring opening to form a stable merocyanine isomer or distribution of isomers is complete within 50 ps and that this isomer(s) distribution formed remains unchanged for at least 1.5 ns.

Femtosecond-picosecond laser photolysis studies on the dynamics of excited charge-transfer complexes in solution. 2. Ion pair formation processes in the excited states of 1,2,4,5-tetracyanobenzene-aromatic hydrocarbon complexes in polar solvents

Femtosecond and picosecond laser photolysis and time-resolved transient absorption spectral studies have been made-to elucidate the photoinduced charge separation (CS) process in the 1,2,4,5-tetracyanobenzene (TCNB)-aromatic hydrocarbon charge-transfer (CT) complexes in various polar solvents. We have confirmed that, in a polar solvent such as acetonitrile, solvent reorientation can induce CS with a time constant shorter than 1 ps to a considerable extent but not completely. Moreover, we have demonstrated that, for the complete CS leading to the ion-pair formation, further intracomplex structural change and solvation, which take place with a time constant (τ CS ) of several picoseconds to 30 ps depending on the natures of the electron-donating aromatic hydrocarbon and the polar solvent, are necessary

Transient spectroscopy of a photochromic fulgide

The kinetics of the photochromic transformation of the fulgide 2-[1-(2,5-dimethyl-3-furyl)ethylidene]-3-isopropylidenesuccinic anhydride have been studied by means of picosecond time-resolved absorption and emission spectroscopy. The steady state emission of this fulgide has been investigated also. The photochromic process is shown to be very fast at room temperature, occurring within twenty picoseconds.