Temperature effects fluorescence

Attention should be paid to possible problems in the measurement of fluorescence quantum yields (some of which are discussed Section 6.1.5) inner filter effects, possible wavelength effects on Op, refractive index corrections, polarization effects, temperature effects, impurity effects, photochemical instability and Raman scattering. 

Using the temperature effect, it was proven that non-emitting exciplex intermediates were also involved in the cycloaddition. For example, in the reaction of naphthalene with diphenylacetylene, with increasing temperature both the quantum yields of photoaddition and the quenching of the naphthalene fluorescence by acetylene decrease by the same magnitude [65],... 

Temperature Effect on Fluorescence of the Ethidium Bromide-DNA Complex... 

Describe the temperature effects on fluorescence intensity, anisotropy, and lifetime. 

In addition to chemical reaction, weak fluorescence was detected from 50 at room temperature (acxc 460 nm, Xem 552 nm, cj)f = 0.04). Temperature effects on reaction and fluorescence from 77-310 K have been studied 68). A steady decrease in quantum yield for reaction (r) and a complementary increase in fluorescence quantum yield (< )f) were observed down to about 150K where a sharp increase in f occurred. Photochemical reaction was negligible at 77 K (436 nm). The fluorescence lifetime at 77 K was a few nanoseconds and the estimated value at room temperature is on the order of 60 ps. Detailed analysis of the data showed that two thermally-activated processes are involved (1) chemical reaction of the singlet state with an Arrhenius activation energy of 1.5 kcal/mol and (2) radiationless decay of the singlet with Eact =1.1 kcal/mol. Both processes would appear to be associated with certain vibrational modes of the excited state which become progressively less populated with decreasing temperature. 

Work on indole, tryptophan, etc. continues because of their relevance to the complex field of protein photophysics. Creed has produced reviews of the photophysics and photochemistry of near-u.v.-absorbing amino-acids, viz. tryptophan and its simple derivatives, tyrosine and its simple derivatives, and cysteine and its simple derivatives. The nature of the fluorescent state of methylated indole derivatives has been examined in detail by Meech et al. Another investigation on indole derivatives deals particularly with solvent and temperature effects. Fluorescence quenching of indole by dimethylfor-mamide has also been examined in detail. Fluorescence excitation spectra of indoles and van der Waals complexes by supersonic jets give microscopic solvent shifts of electronic origin and prominent vibrational excitation of L(, states. Conventional flash photolysis of 1-methylindole in water shows R, e p, and a triplet state to be formed. " Changes in the steady-state fluores-... 

The fluorescence intensity of quinoline derivatives has been found to increase dramatically with an increase in the molecular weight of the host polystyrene. " This is attributed to a decrease in the free volume in the polymer matrix restricting molecular rotation/motion of the fluorophore. Similar effects have been observed for juliodinemalononitrUe in different stereo-regular poly(methyl methacrylates), and temperature effects on the luminescence properties of indole and coumaric acid derivatives in different polymer matrices showed abrupt changes in emission intensity at temperatures which correspond to the onset of local relaxation processes in the polymer. ... 

The presence of oxygen is critical because the interaction of oxygen with the sample can cause serious errors, and its ability to quench not only the fluorescence but also phosphorescence makes deaeration necessary. Also, the photoluminescence intensity usually decreases when the temperature of the sample is increased this is attributed to the higher probability for other nonradiative deactivations in the excited state of the molecule. Therefore, to minimize such temperature effects, the photoluminescence spectra are often measured at liquid-nitrogen temperature and even liquid-helium temperature (33, 34, 36-38, 49-53). 

When the fluorescence method becomes more generally adopted, it will be necessary to study not only those factors (neutral salt, temperature) which alter the equilibrium relationships, but also those which influence fluorescence (deformation effect, influence of solvent, etc. cf. P. W. Danckwortt, Luminescence Analysis, 2 Ed., Leipzig 1929 F. Weigebt, Optical Methods in Chemistry, 1927). The interesting publication of L. J. Desha should be consulted regarding the quantitative aspects of fluorometry. In quantitative work it is best to use the filtered monochromatic ultraviolet radiation (X = 366 mm) from a quartz lamp. Con-... 

Here we report preliminary results on the multiple fluorescence emission of 1 and 2. From structure-property relationships, solvent effect and temperature effect studies, we are able to show that the multiple emission is from the emission of free squaraine in solution, the emission of the solute-solvent complex and the emission of a twisted relaxed excited state. Further solvent effect study using 2 as a model shows that squaraine forms strong solute-solvent complexes with alcoholic solvent molecules. Analogous complex-ation process is also detected between 1 and the hydroxy groups on the macromolecular chains of poly(vinyl formal). The Important role of this complexation process on the stabilization mechanism of particles of 1 in polymer solution is discussed. 

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