Optical properties, spectroscopy phosphorescence

Spectroscopies such as UV-visible absorption and phosphorescence and fluorescence detection are routinely used to probe electronic transitions in bulk materials, but they are seldom used to look at the properties of surfaces [72]. As with other optical techniques, one of the main problems here is the lack of surface discrimination, a problem that has sometime been b q)assed by either using thin films of the materials of interest [73, 74], or by using a reflection detection scheme. Modulation of a parameter, such as electric or magnetic fields, stress, or temperature, which affects the optical properties of the sample and detection of the AC component of the signal induced by such periodic changes, can also be used to achieve good surface sensitivity [75]. This latter approach is the basis for techniques such as surface reflectance spectroscopy, reflectance difference spectroscopy/reflectance anisotropy spectroscopy, surface photoadsorption... 

The optical and PL spectroscopies have been undertaken to understand the structure-property correlations of this important family of triplet-emitting polymers. The red shift in the absorption features upon coordination of the metal groups is consistent with there being an increase in conjugation length over the molecule through the metal center. The trade-olf relationship between the phosphorescence parameters (such as emission wavelength, quantum yield, rates of radiative and nonradiative decay) and the optical gap will be formulated. For systems with third-row transition metal chromophores in which the ISC efficiency is close to 100%,76-78 the phosphorescence radiative (kr)y, and nonradiative (/cm)p decay rates are related to the measured lifetime of triplet emission (tp) and the phosphorescence quantum yield ([Pg.300]

During the past five years two research disciplines of optical spectroscopy and magnetic resonance have merged when it became evident that at low temperatures, microwave radiation of resonance frequencies with the zero-field (zf) transitions of the lowest triplet state could have observable effects on the phosphorescence intensity as well as the spectrum. Quantitative information can then be obtained from these phosphorescence-microwave multiple-resonance experiments from which the magnetic, the radiative, and the nonradiative as well as the structural properties of the triplet state can be determined. 

The most investigated thioketones have found applications in the pharmaceutical, polymer, pesticide, and herbicide industries. However, there is increasing interest in their photophysic and non-linear electric properties, which make them interesting molecules for fluorescence and phosphorescence spectroscopy, and promising building blocks for non-linear optical materials. Studies concerning the addition of a hydrogen atom to C=S, the environment" and the C NMR for thioketones and selenoketones have been also carried out. 

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