Picosecond absorption

Sundstrdm V and Gillbro T 1984 Dynamics of the isomerization of trans-stiibene in n-alcohols studied by ultraviolet picosecond absorption recovery Chem. Phys. Lett. 109 538-43... 

Pullerits T, Visscher K J, Hess S, Sundstrom V, Freiberg A, Timpmann K and Van Grondelle R 1994 Energy-transfer in the inhomogeneously broadened core antenna of purple bacteria-a simultaneous fit of low-intensity picosecond absorption and fluorescence kinetics Biophys. J. 66 236-48... 

Rulliere C, Grabowski ZG, Dobkowski J (1987) Picosecond absorption spectra of carbonyl derivatives of dimethylaniline the nature of the TICT excited states. Chem Phys Lett 137(5) 408 113... 

Fig. 3 Electronic absorption spectra of (A) the EDA complex of 9-cyanoanthracene (CNA) and tetracyanoethylene (TCNE) in comparison with the uncomplexed CNA and TCNE (B) the donor cation CNA+- and acceptor anion TCNE -generated spectroelectrochemically and (C) time-resolved picosecond absorption spectra taken at 25, 50, 75 and lOOps following the charge-transfer excitation at 532 nm of [CNA, TCNE] with a 25-ps laser pulse.

Fig. 5 (A) Typical time-resolved picosecond absorption spectrum following the charge-transfer excitation of tropylium EDA complexes with arenes (anthracene-9-carbaldehyde) showing the bleaching (negative absorbance) of the charge-transfer absorption band and the growth of the aromatic cation radical. (B) Temporal evolution of ArH+- monitored at Amax. The inset shows the first-order plot of the ion...

Pairwise EET rates cannot be directly measured in antenna systems. The closest approach to direct determination is offered on the one hand by time resolved picosecond and sub-picosecond absorption and fluorescence measurements and on the other hand by hole burning spectroscopies. Time resolved techniques do not detect transfer between isoenergetic sites. A somewhat more indirect approach to determining pairwise rates is that of analysing excited state lifetime data in terms of a particular antenna and an EET model. 

Wasielewski, M. R. Kispert, L. D. unpublished picosecond absorption results. 

In this report we would like to discuss our results on the picosecond photodissociation experiments of the CO and O2 forms of a number of synthetic reversible oxygen carriers (1,2) and compared them to earlier picosecond absorption work on the same derivatives of the natural forms of hemoglobin. The latter work has provided us with a better understanding of the details of the photodissociation in terms of the sequential evolution of four photointermediates which were experimentally isolated, characterized, and kinetically analyzed (3,4). 

Caldwell, K, Noe, L. J, Traylor, T. G. "Photodissociation of Carbon Monoxide Forms of Synthetic Heme Complexes Using Picosecond Absorption Spectroscopy", unpublished results, National ACS Meeting, Miami Beach, April 1985. 

The time and wavelength resolved fluorescence dynamics of bianthryl has been investigated by several groups [30, 82, 132, 133, 115, 116]. In addition, this molecule has been studied by picosecond absorption spectroscopy [115], electric field induced fluorescence anisotropy measurements [117] and optically induced dielectric absorption (microwave) measurements [118, 119]. The results are generally in accord with the theoretical model presented in Sections III.A and III.B. One of the challenges of studying the photodynamics of BA is that the LE and CT interconversion is so rapid (i.e., on the time scale of solvation) that it is necessary to employ ultraviolet subpicosecond and even femtosecond fluorescence spectroscopy which has only recently become available [30, 82, 132, 133]. 

Picosecond absorption spectroscopy was employed to study the dynamics of contact ion pairs produced upon the photolysis of substituted diphenylmethyl acetates in the solvents acetonitrile, dimethyl sulfoxide, and 2,2,2-trifluoroethanol.66 A review appeared of the equation developed by Mayr and co-workers log k = s(N + E), where k is the rate constant at 20 °C, s and N are nucleophile-dependent parameters, and is an electrophilicity parameter 67 This equation, originally developed for benzhydrylium ions and n-nucleophiles, has now been employed for a large number of different types of electrophiles and nucleophiles. The E, N, and s parameters now available can be used to predict the rates of a large number of polar organic reactions. Rate constants for the reactions of benzhydrylium ions with halide ions were obtained... 

Picosecond absorption spectroscopy studies of the contact ion pairs formed in the photo-initiated, S N 1 reaction of three substituted benzhydryl acetates (18) provided the rate constants for the k and k2 steps of the reaction (Scheme 10), in acetonitrile and DMSO.83 The activation parameters for the k and k2 steps were obtained from the temperature dependence of these steps and the transition state energies were calculated from the rate constants. This allowed the energy surfaces for three substituted substrates to be calculated in each solvent. The effect of solvent reorganization on the reactions of the unsubstituted and methyl-substituted benzhydryl contact ion pairs (CIP) was significant, causing a breakdown of transition state theory for these reactions. The results indicated that it will be very difficult to develop a simple theory of nucleophilicity in, S N1 reactions and that Marcus theory cannot be applied to SnI processes. 

In this system, the dynamics of pair decay (via intersystem crossing) and of pair separation by solvent molecules were determined by picosecond absorption spectroscopy [167, 168],... 

Concerning the analysis of different types of ion pairs and their discrimination using picosecond absorption spectroscopy, the work by Peters must be emphasized. He studied in great detail the photoreduction of benzophenone by aromatic amines... 

No evidence was found from the picosecond absorption data for an excited state intermediate of the EDA complex. This formulation represente a confirmation of Mulliken s theory, in which CT band excitation of the quite nonpolar ground state produces an ion pair. Accordingly, indene and TCNE form ground state complexes which undergo fast electron transfer on irradition. However, back electron transfer occurs after relatively long time (ca. 500 ps) via a transient... 

Lepore, G. P. Langford, C. H. Vichova, J. Vlcek, A. J. Photochemistry and picosecond absorption spectra of aqueous suspensions visible spectrum, J. Photo-chem. Photobiol. 1993, A75, 67. 

The properties of excited states of several halonaphthalenes and haloanthracenes have been investigated by means of picosecond absorption and emission spectroscopy388,389. Fluorescence measurements showed the expected heavy-atom effect due to spin-orbit coupling. Fluorescence lifetimes of the chloronaphthalenes in hexane were the longest, 2.4 and 3.3 ns for 1-chloro- and 2-chloronaphthalene, respectively. The 1-bromo and 2-bromo... 

Figure 8. Ultrafast processes associated with bathorhodopsin and hypsorhodopsin monitored by picosecond absorption spectroscopy. (A) Absorbance changes (aA) as function of time monitored at 530 nm, showing the decay of a species (PBAT) identified as the precursor of BAT. (B) Arrhenius plot for the rate constant of this process in rhodopsin and in deuterated rhodopsin. (C) Decay of hypsorhodopsin. (D) Formation of bathorhodopsin. [(A) and (B) data from ref. 301 for bovine rhodopsin (in 0.1 M Ammonix LO, 66% ethylene glycol, at pH 7.0). (C) and (D) data from ref. 298 for squid rhodopsin in 2% digitonin (pH 10.5) at room temperature.]...

Shen Y, Cook AR. (2009) Optical fiber-based single-shot picosecond absorption spectroscopy. Rev Set Instrum 80 073106. 

Ono and Ware"" have measured the absorption, emission, and excitation spectra, the fluorescence decay times, and the quantum yields of a series of substituted diphenylmethylenes in rigid matrices at low temperatures. Acean-thrylene shows S2- So emission in hexane with a yield of 0.017 and lifetime of 4.3 ns. The low-temperature fluorescence spectra of bis-2-naphthyl-alkanes and their derivatives have been studied. Excimer formation is an activated process. The fluorescence and absorption spectra of 1,1-diphenyl-ethylenes have been analysed in some detail by Gustav and Bolke. " The S — Si transitions in trans isomers of phenylnaphthylethylenes have been assigned by picosecond absorption spectroscopy. Effects of solvent viscosity and the role of conformers in the mechanism of isomerization are elucidated. The production of non-equilibrium conformer concentrations in glassy solutions of diarylethylenes at 77 K due to restrictions imposed by the solid matrix has also been reported. Free jet excitation and emission spectra of diphenyl-butadiene show clearly the lowest excited Ag state and give a lifetime of 52.8 ns for 0-0 excitation.Electric field-induced charges in the optical... 

A transient absorption band, with a profile similar to that of the dimethylani-line radical cation, was observed in polar solvents by time-resolved picosecond absorption spectroscopy. 

B Ke and VA Shuvaiov (1987) Picosecond absorption spectroscopy In photosynthesis and primary electron transfer processes, in J Barber (ed) Topics in Photosynthesis, Voi 8, The Light Reactions, pp 31-93. Eisevier... 

Picosecond spectroscopy enables one to observe ultrafast events in great detail as a reaction evolves. Most picosecond laser systems currently rely on optical multichannel detectors (OMCDs) as a means by which spectra of transient species and states are recorded and their formation and decay kinetics measured. In this paper, we describe some early optical detection methods used to obtain picosecond spectroscopic data. Also we present examples of the application of picosecond absorption and emission spectroscopy to such mechanistic problems as the photodissociation of haloaromatic compounds, the visual transduction process, and inter-molecular photoinitiated electron transfer. 

Picosecond spectroscopy provides a means of studying ultrafast events which occur in physical, chemical, and biological processes. Several types of laser systems are currently available which possess time resolution ranging from less than one picosecond to several picoseconds. These systems can be used to observe transient states and species involved in a reaction and to measure their formation and decay kinetics by means of picosecond absorption, emission and Raman spectroscopy. Technological advances in lasers and optical detection systems have permitted an increasing number of photochemical reactions to be studied in. greater detail than was previously possible. Several recent reviews (1-4) have been written which describe these picosecond laser systems and several applications of them... 

Figure 1. (A) Apparatus used for time-resolved picosecond absorption spectroscopy which utilizes the TPF technique. A set ofphotodiodes and oscilloscopes (PI, P2, P3, and P4)are used to measure the intensity of the laser pulse before and after each pass through the cell. (Reproduced with permission from Ref 15. Copyright 1969, North-Holland...

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