Phosphorescence polarization

Fluorescence and phosphorescence spectra corrected for the instrumental sensitivity were measured with a spectrometer described previously (()). Corrected excitation spectra were obtained with constant excitation intensity controlled by a rhodamine B quantum counter. For phosphorescence polarization measurements the apparatus was set up in an "In Line" arrangement (j ) and equipped with a Glan-Thomson polarizer and a sheet polarizer (analyser) (10). 

In order to corroborate the existence of energy transfer we studied the phosphorescence polarization. While the directly excited phosphorescence of MBC in... 

Spectroscopic data of nitroaromatics have been reviewed D in addition, several papers on luminescence of nitroaromatic compounds have appeared recently. The phosphorescence polarization of several aromatic nitro compounds has been studied and recent triplet-triplet absorption data on 1- and 2-nitro-naphthalene have become available ). 

Experimentally, the direction of a transition moment in a molecule can he evaluated by four methods (i) polarized spectra of single crystals, (ii) fluorescence or phosphorescence polarization, (iii) spectra of molecules embedded in stretched Aims, and (iv) spectra of molecules oriented by external fields. Only relative directions of the transition moment can be determined by means of the last three methods, whereas the polarized spectra of single crystals give the absolute direction of the moments if the crystal structure is known. The first method has been applied to the study of the electronic structure and spectra of several pyrimidine bases of nucleic... 

The observed phosphorescence polarization direction may be accounted for by the fact that singlet-triplet transitions acquire their intensity by spin-orbit coupling of the Sg state with triplet states and particularly, of the T, state with singlet states. (Cf. Section 1.3.2.) Under usual conditions the phosphorescence is an unresolved superposition of emissions from the three components of the triplet state, which in the absence of an external magnetic field are described... 

The phosphorescence polarization direction is again perpendicular to the molecular plane and is modified by out-of-plane vibrations. 

Phosphorescence Polarization Measurements. The degree of polarization was determined as a function of temperature for the systems P/ACE, P/VN and P-Np (dispersed naphthalene probe). The excitation wavelength was 310 nm and that of analysis, 490 nm. The onset of depolarization was observed at ca. 210, 195 and 180K for P/ACE,... 

In the frame of CSTPM, the following dynamics parameters of the cascade system components can be experimentally measured the spin label rotation correlation time and spin relaxation parameters, the fluorescence and phosphorescence polarization correlation times, the singlet and triplet state quenching rate constants, the rate constant of photoisomerization, and the rate constant of the triplet-triplet energy transfer. This set of parameters is a cumulative characteristic of the dynamic state of biomembranes in the wide range of the probes amplitude and characteristic time. 

The most straightforward way to produce partially oriented solute molecules is to orient them in anisotropic solvents. Good solute orientation can be achieved in stretched polymer sheets [94, 95, 96]. Homogeneously oriented nematic liquid crystals are perfectly clear and are thus excellently suited as anisotropic solvents for optical polarization experiments. Moreover, the liquid crystal method allows the performance of polarization experiments in fluid media. This unique feature of the liquid crystal method can be exploited for polarization studies of metastable molecular species (e.g. excited complexes) formed by a diffusion-controlled process. The ordered glasses produced by rapid cooling of a uniformly aligned nematic phase can be used for phosphorescence polarization experiments. 

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