Diffuse reflectance laser flash-photolysis

Alvaro, M., Atienzar, P., Bourdelande, J.L., and Garda, H. (2004) An organically modified single wall carbon nanotube containing a pyrene chromophore Fluorescence and diffuse reflectance laser flash photolysis study. Chem. Phys. Lett. 384, 119-123. 

Schmidt, J.A., Heitner, C., Kelly, G.P., Wilkinson, F.W., "Observation of Light-Induced Transients in Thermomechanical Pulp Using Diffuse-Reflectance Laser-Flash Photolysis". Proceedings of the 1989 International Symposium on Wood and Pulping Chemistry, Raleigh, N.C., 1989. 

Diffuse Reflectance Laser Flash Photolysis of Thermomechanical Pulp... 

The observable parameter in diffuse reflectance laser flash photolysis experiments is the fractional reflectance change AJ(t)/J0 defined as in Equation 1. 

Figure 1. Schematic Diagram of the Apparatus and Optical Arrangement used for Diffuse Reflectance Laser Flash Photolysis Experiments.

Gopidas, K. R. Kamat, P. V. George, M. V. Photochemical processes on oxide surfaces. A diffuse reflectance laser flash photolysis study, Mol. Cryst. Liq. Cryst. 1990, 183, 403. 

Diffuse reflectance laser flash photolysis of a number of ketones on silica and zeolites show that triplet decay kinetics are complex. The effect of temperature on the luminescence... 

Amao, Y., Asai, K., and Okura, I. (2000). A novel optical oxygen sensing system based on triplet-triplet reflectance of fullerene Cgg-polystyrene film by time-resolved spectroscopy using diffuse reflectance laser flash photolysis. Analyst, 125, 523-fi. 

Upper triplet states of biphenyls in micelles ionize to produce hydrated electrons . Diffuse reflective laser flash photolysis has been used to characterise the triplet states of p-terphenyl generated in powder systems. Other triplet states which have been characterised include those of naphthalene and acenaphthene in the solid state", those involved in photoreactions of tetracene with anthracene and 9-bromoanthrene", phenanthrene and biphenylene, highly excited triplet states... 

The mechanism of the quenching of triplet benzophenenone by both electron and hydrogen donors involves change transfer effects". Diffuse reflectance laser flash photolysis studies of the reactions of triplet benzophenone with hydrogen atom donors on surfaces have also been reported". A dual phosphorescence of benzophenone at 77K in HjO/EtOH in glasses indicates that in this environment a... 

In highly scattering materials, absorbance is not directly observable, and changes in diffnse reflectance after the laser flash are monitored instead. Wilkinson and Kelly have described details of the techniqne [157]. Hurrell et al. [151] used diffuse-reflectance laser-flash photolysis to stndy the behavior of several... 

JA Schmidt, C Heitner, GP Kelly, and F Wilkinson. Diffuse-Reflectance Laser-Flash Photolysis of Mechanical Pulp. Part 1. Detection and Identification of Transient Species in the Photolysis of Thermomechanical Pulp. J. Pulp Paper Sci. 16 1111-1117, 1990. 

F Wilkinson, A Goodwin, and DR Worrall. Diffuse Reflectance Laser Flash Photolysis of Thennomechanical Pulp. In C Heitner and 1C Scaiano, eds. Photochemistry of Ligrwcellulosic Materials, 531. Washington, DC American Chemical Society, 1993, pp. 86-98. 

FIGURE 2 - Schematic diagram of the apparatus used in diffuse reflectance laser flash photolysis... 

FIGURE 3 - A typical set of experimental traces obtained using Diffuse Reflectance Laser Flash Photolysis for a microcrystalline sample of benzil (excitation at 354 nm and analysis at 520 nm). 

F. Wilkinson and C.J. Willsher, Tetrahedron 43, (1987) 1197. F. Wilkinson and G.P. Kelly, Handbook of the Photochemistry of organic Compounds in Condensed Media Chapter on diffuse reflectance laser flash photolysis., Ed. J. Scaiano (CRC Press - Florida) (1988) in press. 

A bimolecular photoreaction between different reagents in a solid cyclodextrin phase occurred upon photolysis of crystalline ternary P-CD com[flexes (1 1 2 nitro/amine/p-CD) (Scheme 29) [56a]. Study by diffuse reflectance laser flash photolysis was performed and an observed transient was assigned to the radical anion of 4-nitroveratrole (X = Y = OMe) generated via photoiriduced... 

There has been very little work completed in reverse micelles. This may be due to the increased complexity of these systems, where probe migration and micelle clustering occurs on time scales similar to triplet decay. In addition, litde work has been carried out in vesicles or liposomes. With the advent of diffuse reflectance laser flash photolysis, the turbid solutions observed for large vesicles no longer represent a stumbling block [196-198]. Thus, we believe that, in the future, much more work will be available in vesicular systems that will be able to complement the studies already completed in micelles. 

In a diffuse-reflectance laser flash-photolysis experiment, the excited chro-mophores created by the laser excitation may exhibit a nonhomogeneous spatial distribution. Theoretical treatments (Kessler et al. [10b] and Oelkrug et al. [12]) have shown that two extreme types of concentration profiles can be produced. In the first type, the concentration of excited species decreases exponentially as a function of the penetration depth of the excitation radiation whereas, in the second type, the excited species are distributed in a homogeneous manner within a specific width, and then decrease ( plug profile) as in [lOf, lOg]. 

Wilkinson et al. developed, at the end of the 1980s, the diffuse reflectance laser flash-photolysis technique [1,10], which proved to be crucial for transient absorption and emission studies on surfaces, providing both spectroscopic and kinetical information. This technique for studying solid and opaque media became so important for surface studies as the conventional flash-photolysis was and still is for transparent media, after its discovery by G. Porter in the 1950s. 

The use of triplet excited states as probes to study the surface properties of many solids is particulary interesting, due to the fact that they usually exhibit long lifetimes which in most cases come closer to those obtained for rigid matrices. These long lifetimes increase in many cases the efficiency of several photochemical processes. Therefore spectroscopic and kinetic studies can be performed in a wide and interesting variety of situations. As we said before, the development of the diffuse reflectance laser flash photolysis technique [1,10] by Wilkinson et al. was crucial for the development of these studies on surfaces. 

Diffuse reflectance laser flash photolysis and laser-induced luminescence, hoth in time-resolved mode or ground-state absorption spectroscopy in the diffuse reflectance mode, are important techniques that have been used by several research groups to study opaque and crystalline systems [1—8]. These solid-state photochemical methods have been applied by us to study several organic compounds adsorbed onto different hosts such as microcrystalline cellulose [7, 8], p-tertbutylcalix[n]arenes (n = 4, 6, and 8) and their derivatives [10—12], silicalite, cyclodextrins [7, 12, 13], and silica [l4j. 

Laser-Induced Luminescence (LIL) and Diffuse Reflectance Laser Flash Photolysis (DRLFP) Systems... 

Time-resolved absorption spectra of samples of BZP/C12- 1700/EtOH and Cl 2-I5OO/H2O samples were obtained by the use of diffuse reflectance laser flash photolysis technique, developed by Wilkinson et al. [2-4]. In this study, the use of an intensified charge-coupled device as a detector allowed us to obtain time-resolved absorption spectra with nanometer spectral spacing (i.e., where the 200-900 scale is defined by the 512 pixels used for recording spectra in the array of the ICCD) [1,8-14]. 

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