Picosecond lasers fluorescence spectroscopy

Hydrogen transfer in excited electronic states is being intensively studied with time-resolved spectroscopy. A typical scheme of electronic terms is shown in fig. 46. A vertical optical transition, induced by a picosecond laser pulse, populates the initial well of the excited Si state. The reverse optical transition, observed as the fluorescence band Fj, is accompanied by proton transfer to the second well with lower energy. This transfer is registered as the appearance of another fluorescence band, F2, with a large anti-Stokes shift. The rate constant is inferred from the time dependence of the relative intensities of these bands in dual fluorescence. The experimental data obtained by this method have been reviewed by Barbara et al. [1989]. We only quote the example of hydrogen transfer in the excited state of... 

We have performed super-resolution infrared microscopy by combining a laser fluorescence microscope with picosecond time-resolved TFD-IR spectroscopy. In this chapter, we have demonstrated that the spatial resolution of the infrared microscope improved to more than twice the diffraction limit of IR light. It should he relatively straightforward to improve the spatial resolution to less than 1 pm by building a confocal optical system. Thus, in the near future, the spatial resolution of our infrared microscope will be improved to a sub-micron scale. 

We summarize here two time-resolved spectroscopic methods, giving direct information on picosecond and nanosecond photodynamics of solid surface. One is a fluorescence spectroscopy which analyzes fluorescence behavior of the surface area excited by the evanescent laser pulse. The other is to get transient UV-visible absorption spectra by using the evanescent light as a probe beam. 

Deactivation of 2-naphthylamine singlet state by pyridines in enhanced by dipole moment and the ability to form hydrogen bonds. Picosecond laser spectroscopy shows charge transfer from the excited amine. The fluorescence of 2-iV,A -dimethylaminopyridine induced by p-nitroaniline is also caused by exciplex formation. The latter enhances triplet population of p-nitroaniline. The quenching of the fluoresence of carbazole and some derivatives by trichloroacetic acid and related compounds in fluid solutions has been studied by Johnson.A charge-transfer interaction is involved and the basicity of carbazole and derivatives determined. Charge transfer is also involved by quenching of carbazole by halocarbons. The A -isopropylcarbazole-dimethylterephthalate exciplex has been observed in PMMA films.Photoinduced electron-transfer in the p-phenylenediamine-paraquat complex yields the paraquat cation. ... 

The development of picosecond laser techniques has led to a renewed interest in the spectroscopy and kinetics of aromatic molecules which may undergo excited state intramolecular proton transfer (ESIPT, fig. 1). The ESIPT reaction is evidenced by a large Stokes shift for fluorescence from the proton-transferred molecule. ... 

Everall N, Hahn T, Matuosek P, Parker A, Towrie M (2001) Picosecond time-resolved Raman spectroscopy of solids capabilities and limitations for fluorescence rejection and the influence of diffuse reflectance. Appl Spectrosc 55 1701-1708 Gaft M, Nagli L (2008) Laser-based spectroscopy for standoff detection of explosives. Opt Mater... 

Time-resolved fluorescence spectroscopy is also a valuable tool in biological and medical research [10.143-147]. Since the lifetimes involved are normally short, picosecond spectroscopy techniques are frequently employed (Sect. 9.4). Examples of fluorescence decay curves for tissue recorded with delayed coincidence techniques employing a frequency-doubled picosecond dye laser are depicted in Fig. 10.42. The decay characteristics allow the discrimination between tumour and normal tissue, and atherosclerotic plaque and normal vessel wall, respectively. General surveys of the use of LIF for medical diagnostics can be found in [10.148,149]. 

N.S. Bergano, P.A. Janimaagi, M.M. Salour, J.H. Bechtel Picosecond laser-spectroscopy measurement of hydroxyl fluorescence lifetime in flames. Opt. Lett.8, 443 (1983)... 

The temperature dependence of fluorescence shows that tram cis photoisomerization as a competing path is activated the activation energy (Ej ,) lies in the 15-30 kj mol range (Table 36.2). The viscosity dependence of intensively studied by picosecond laser spectroscopy. 2 The relaxation rates of... 

This agrees quite well with the rate constants for intramolecular proton transfer in 2,4-bis(dimethyl-amino )-6-(2-hydroxy-5-methylphenyl)-5-triazine which had been measured by Shizuka et al. ( l6) using laser picosecond spectroscopy. The fluorescence decay constant t of (TIN) was found to be 60 20 ps. Because of the weak intensity all fluorescence lifetimes refer to the pure substance in crystalline form at room temperature. 

The rotational reorientation times of the sample in several solvents at room temperature were measured by picosecond time-resolved fluorescence and absorption depolarization spectroscopy. Details of our experimental setups were described elsewhere. For the time-correlated single photon counting measurement of which the response time is a ut 40 ps, the sample solution was excited with a second harmonics of a femtosecond Ti sapphire laser (370 nm) and the fluorescence polarized parallel and perpendicular to the direction of the excitation pulse polarization as well as the magic angle one were monitored. The second harmonics of the rhodamine-640 dye laser (313 nm 10 ps FWHM) was used to raesisure the polarized transient absorption spectra. The synthesis of the sample is given elsewhere. All the solvents of spectro-grade were used without further purification. 

Luminescence measurements have been made on 2,5-distrylpyrazine and l,4-bis-( 3-pyridyl-2-vinyl)benzene in mixed crystals between 8 and 300 K. Solvent and pH dependences of the fluorescence spectra of 9-phenanthrylamine have been used to determine pK values. Picosecond and nanosecond laser spectroscopy have been used to study the photoenolization of 2-methylbenzo-phenone. ... 

The laser-excited fluorescence from dibenzofuran in a biphenyl host at 4.2 K and three different sites in the lattice have been identified. The two-photon excitation spectrum of single crystals of carbazole at 4.2 K has been analysed in detail. Very extensive vibrationally unrelaxed fluorescence is observed following dye-laser excitation of single vibronic levels of naphthazanine and the rates and pathways of relaxation are examined by picosecond emission spectroscopy. The photophysics of rubrene peroxide have been measured for the first time by Bayrakceken. Picosecond fluorescence has been used to study the spectra and kinetics for Sj— So and Si transitions for... 

Photoprocesses in biliverdin dimethyl ester in ethanol have been studied by laser-induced optoacoustic spectroscopy." The picosecond kinetics of excited-state relaxation of this ester have also been reported." " Isophorcarubin is a conformationally restricted and highly fluorescent bilirubin." " The phototherapy for neonatal jaundice has stimulated investigations of configurational isomers of bilirubin" and of stereospecific and regioselective photoisomerization of bilirubin." ... 

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