Luminescence solvent effects

Luminescence is often much more sensitive to molecular dynamics than other optical techniques where temperature, viscosity, pH and solvent effects can have a significant influence on the emission response. Analyte degradation for light sensitive fluors and photobleaching for static measurements also influence the emission signal. Because of the wide variety of potential matrix effects, a thorough investigation should be conducted or the sample matrix well understood in terms of its potential impact on emission response. A complete discussion on the fate of the excited states and other measurement risk considerations can be found elsewhere. ... 

The molecule is often represented as a polarizable point dipole. A few attempts have been performed with finite size models, such as dielectric spheres [64], To the best of our knowledge, the first model that joined a quantum mechanical description of the molecule with a continuum description of the metal was that by Hilton and Oxtoby [72], They considered an hydrogen atom in front of a perfect conductor plate, and they calculated the static polarizability aeff to demonstrate that the effect of the image potential on aeff could not justify SERS enhancement. In recent years, PCM has been extended to systems composed of a molecule, a metal specimen and possibly a solvent or a matrix embedding the metal-molecule system in a molecularly shaped cavity [62,73-78], In particular, the molecule was treated at the Hartree-Fock, DFT or ZINDO level, while for the metal different models have been explored for SERS and luminescence calculations, metal aggregates composed of several spherical particles, characterized by the experimental frequency-dependent dielectric constant. For luminescence, the effects of the surface roughness and the nonlocal response of the metal (at the Lindhard level) for planar metal surfaces have been also explored. The calculation of static and dynamic electrostatic interactions between the molecule, the complex shaped metal body and the solvent or matrix was done by using a BEM coupled, in some versions of the model, with an IEF approach. 

Theoretical calculations on the nature of solvent effects which affect the n-Jt blue shifts for pyrimidine, pyridazine, and pyrazine have been compared with the results of experimental observation . A theoretical study of electronic spectra and photophysics of uracil derivatives , the luminescence of 4-phenylpyridine and... 

A theoretical paper discusses the nature of solvent effects which affect the deactivation of A 02 . The effect of hydrostatic pressure on the radiationless deactivation of 03 in solution has also been reported . The perturbing effects of the solvents H2O, DjO, and QH5CH3 on the luminescence rate constant of O2 up to 100 atm provide evidence for pardcipation of complexes involving both the ground and excited states of molecular oxygen . The application of a collision complex model has been applied to the interpretation of photophysical quenching of 03 in liquids by 4-amino-TEMPO . 

A review (in German) has appeared concerned with the effects of microenvironment upon the luminescence properties of molecular species,480 and one in English also on solvent effects.481 Temperature effects on solvent parameters,481 a model for the ab initio calculation of solvent effects,482 and the reorientation of hydrogen-bonded solvents around a large dipole483 have been discussed. 

Luwang, M.N., Ningthoujam, R.S., Jagannath, Srivastava, S.K., Vatsa, R.K., 2010. Effects of Ce codoping and anneahng on phase transformation and luminescence of Eu -doped YPO4 nanorods D2O solvent effect. J. Am. Chem. Soc. 132, 2759—2768. 

Inorganic phosphors are potential labels for time-resolved luminescence staining and assays in aqueous environment [23, 52-55]. The lanthanide phosphors have essentially infinite shelf life, no toxicity, no photobleaching, and are unaffected by environmental conditions such as pH, temperature, enzymatic reactions, or solvent effects. Their major drawback is that the luminescence per lanthanide ion is significantly less than from the dye-doped or dye nanoparticles due to the weak absorption of individual ions partly compensated by their higher number. Inorganic nanoparticles, however, can be prepared readily in large quantities with relatively simple methods. The size of the nanoparticles can be controlled from low nanometer scale to several hundred nanometers with a narrow size distribution. 

Hsu et al. demonstrated the sensing property of an Na[Tb(OBA)2] (OBA = 4,4 -oxybis(benzoate)) MOF [29] the proposed MOF showed the ability to act as a stimuli responsive luminescent material towards a variety of solvents. The luminescence measurements of the MOF displayed that the D4 —> F4 emissions were the strongest intensities in BuOH and EtOH suspensions, but these intensities were significantly reduced in MeOH and H2O suspensions. The small molecules of H2O and MeOH get closer to the terbium ions of the framework that quenches the luminescence intensities effectively on the other hand, the alkyl sterical hindrance of EtOH and BuOH potentially protects the terbium ions from quenching by OH oscillators. 

It is well known, that in aqueous solutions the water molecules, which are in the inner coordination sphere of the complex, quench the lanthanide (Ln) luminescence in result of vibrations of the OH-groups (OH-oscillators). The use of D O instead of H O, the freezing of solution as well as the introduction of a second ligand to obtain a mixed-ligand complex leads to either partial or complete elimination of the H O influence. The same effect may be achieved by water molecules replacement from the inner and outer coordination sphere at the addition of organic solvents or when the molecule of Ln complex is introduced into the micelle of the surfactant. 

It was found that the effect of solvents and various surfactants Triton X-100, Twin-80, Brij-35 sodium laurylsulfate, sodium cetylsulfate, cetylpyridinium chloride, cetyltrimethylammonium bromide on the luminescence intensity is insignificant. 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

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