Thermally assisted fluorescence

Thermally assisted fluorescence is the converse of stepwise line fluorescence. It occurs as a result of a stepwise absorption of energy by... 

In the case of the stepwise line fluorescence, the effect is divided into Stokes and anti-Stokes stepwise fluorescence depending on the wavelength (energy) relationships. A thermally assisted process may take place, if after radiation excitation, further collisional excitation occurs. 

Other techniques that have been used to determine polycyclic aromatic hydrocarbons in soil extracts include ELISA field screening [86], micellar elec-tr okinetic capillary chromatography [ 87], supersonic jet laser-induced fluorescence [88,89], fluorescence quenching [90], thermal desorption gas chromatography-mass spectrometry [81,90,100], microwave-assisted extraction [91], thermal desorption [92], immunochemical methods [93,94], electrophoresis [96], thin layer chromatography [95], and pyrolysis gas chromatography [35]. 

Abbreviations AOD, Acousto-optical deflection BCB, bisbenzyocyclobutadiene CCD, indirect contact conductivity detection CL, chemiluminescence ECD, electron capture detector FCS, fluorescence correlation spectroscopy FRET, fluorescence resonance energy transfer ICCD, integrated contact conductivity detection GMR, giant magnetoresistive LED-CFD, light emitting diode confocal fluorescence detector LIF, laser-induced fluorescence LOD, limit of detection MALDI, matrix-assisted laser desorption ionization PDMS, poly(dimethylsiloxane) PMMA, poly(methylmetha-crylate) SPR, surface plasmon resonance SVD, sinusoidal voltammetric detection TLS, thermal lens spectroscopy. 

The de-excitation path available to conjugated organic molecules is controlled by quantum-mechanical rules which are complex. Some molecules will relax spontaneously, other will not (within a reasonable time) without assistance from another material/mechanism. The presence of Oxygen is a special case. Resonant conjugated molecules with two Oxygen atoms will not fluoresce and there only means of de-excitation is by means of a direct transition that is not allowed because of the presence of the triplet state. The nonresonant conjugates normally de-excite thermally via a two-step process. 

A. Electron-Phonon Interaction Parameterization Scheme. In observing the fluorescence decay rate from a given J-manifold, it is generally found that the decay rate is independent of both the crystal-field level used to excite the system and the level used to monitor the fluorescence decay. This observation indicates that the crystal-field levels within a manifold attain thermal equilibrium within a time short compared to the fluorescence decay time. To obtain this equilibrium, the electronic states must interact with the host lattice which induces transitions between the various crystal-field levels. The interaction responsible for such transitions is the electron-phonon interaction. This interaction produces phonon-induced electric-dipole transitions, phonon side-band structure, and temperature-dependent line widths and fluorescence decay rates. It is also responsible for non-resonant, or more specifically, phonon-assisted energy transfer between both similar and different ions. Studies of these and other dynamic processes have been the focus of most of the spectroscopic studies of the transition metal and lanthanide ions over the past decade. An introduction to the lanthanide work is given by Hiifner (39). 

Continuous emission from NOa 359 and single vibronic level fluorescence from NOa 360 have been reported. The lifetimes of the 2Bl K > 0) states were measured, and the interesting result was obtained that the lifetime of the K = 4, N = 16 1 level was 36 [xs, substantially greater than that of the K = 0 levels. The increase in lifetime is attributed to Renner interaction of the and 2AX components of the linear 2 state. Rotational excitation has been shown to assist in the dissociation of NOa in the 249.1 nm system, but this is minor in extent compared with that observed in the 397.9 nm system. Yields of 0(4)) were reported.361 The photolysis of NOa has been further studied.362 In the report by Harteck et al., a two-photon excitation process was observed when a pulsed ruby laser was used for excitation. Thermal and photochemical reactions of NOa with butyraldehyde,363 other aldehyde-NO systems,364 and methylperoxyl radical-NOx reactions 365 have been discussed. 

The control of inverse transition temperatures by sequence manipulation and biocompatibility of ELPs make them useful polymers for drug delivery. Cultured cancer cells and solid tumors in animal models uptake fluorescently labeled ELPs in a thermally responsive manner (48,49). Two major limitations in cancer therapy have been the inability of therapeutic molecules to cross the cell membrane and the target-specificity of the compounds. To overcome these limitations cell-penetrating, peptides (CPP) have been fused with ELPs (CPP-ELP) to develop thermally responsive therapeutics with the ability to translocate the cell membrane (Figure 3B). CPPs can assist in the transportation of hydrophilic compounds (small molecules, oglionucleotides and peptides) across the cell membrane (50). Fusing ELPs to a variety of CPPs have revealed that the peptide sequence of penetratin demonstrates the most efficient cellular uptake (51). Further, these CPP-ELPs have been fused to a c-Myc inhibitory peptide known to target and inhibit cancer. As proof of principle, these fusion proteins inhibits proliferation of cultured cancer cell lines in a thermally responsive manner (52). 

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