Fluorescence emission and absorption

The presence of metallic surfaces or particles in the vicinity of a fluorophore can dramatically alter the fluorescence emission and absorption properties of the fluorophore. The effect, which is associated with the surface plasmon resonance of the metallic surface, depends on parameters such as metal type, particle size, fluorophore type and fluorophore-particle separation. 

Ying, L., Huang, X., Huang, B., Xie, J., Zhao, J. and Zhao, X.S. (2002) Fluorescence emission and absorption spectra of single Anabaena sp strain PCC7120 cells. Photochem. Photobiol., 76, 310-313. 

Due to the overlap of the monomer fluorescence emission and absorption from the aggregates, a quenching process may occur by a resonance interaction. However, in other cases [85, 86] where we determine the extinction coefficients for ground-state monomers and dimers, by simply taking into account the fraction of the excitation radiation absorbed by the monomers (which are emissive species) and aggregates (from which we could not detect any fluorescence emission), a good superposition between the calculated and experimental fluorescence intensity curve was obtained. 

The ionic liquid viscosity change effect was obtained by the bipolar solvent (DMF). Influence of the ionic liquid viscosity has been detected by the fluorescence emission and absorption spectra. Important information is that the new electronic states of P-carotene were found in the mixture of RTIL and DMF (Bialek-Bylka, 2008). 

Subsequently, 8-nor-8-hydroxy-flavin compounds were synthetized by an analogous procedure and were shown to simulate the spectral parameters of the natural product at the riboflavin level as, for example, in the ESR (Fig. 3), the pH dependence of fluorescence emission and absorption spectra. Thus the structure of the orange chromophore was established as the 8-nor-8-hydroxy-derivative of FAD (18, R = Rib-( )-AMP). Alternatively, a hydroxy function can be introduced into position 8 of the flavin ring by hydrolysis of 8-nor-8-diazonium-flavin compounds 152). 

Poly[2,5-dialkoxy-l,4-phenylene) vinylenejs with long solubilizing alkoxy chains dissolve in conventional organic solvents such as chloroform, toluene, or tetrahydrofuran [21, 28, 32-36]. Their emission and absorption spectra are red-shifted relative to PPV itself, and the polymers fluorescence and electroluminescence quantum yields are greater than parent PPV. This benefit may be a consequence of the long alkyl chains isolating the polymer chains from each other. 

Polar or thermally labile compounds - many of the more modern pesticides fall into one or other of these categories - are not amenable to GC and therefore LC becomes the separation technique of choice. HPLC columns may be linked to a diode-array detector (DAD) or fluorescence detector if the target analyte(s) contain chromophores or fluorophores. When using a DAD, identification of the analyte(s) is based on the relative retention time and absorption wavelengths. Similarly, with fluorescence detection, retention time and emission and absorption wavelengths are used for identification purposes. Both can be subject to interference caused by co-extractives present in the sample extract(s) and therefore unequivocal confirmation of identity is seldom possible. 

Both emission and absorption spectra are affected in a complex way by variations in atomisation temperature. The means of excitation contributes to the complexity of the spectra. Thermal excitation by flames (1500-3000 K) only results in a limited number of lines and simple spectra. Higher temperatures increase the total atom population of the flame, and thus the sensitivity. With certain elements, however, the increase in atom population is more than offset by the loss of atoms as a result of ionisation. Temperature also determines the relative number of excited and unexcited atoms in a source. The number of unexcited atoms in a typical flame exceeds the number of excited ones by a factor of 103 to 1010 or more. At higher temperatures (up to 10 000 K), in plasmas and electrical discharges, more complex spectra result, owing to the excitation to more and higher levels, and contributions of ionised species. On the other hand, atomic absorption and atomic fluorescence spectrometry, which require excitation by absorption of UV/VIS radiation, mainly involve resonance transitions, and result in very simple spectra. 

FRET is a nonradiative process that is, the transfer takes place without the emission or absorption of a photon. And yet, the transition dipoles, which are central to the mechanism by which the ground and excited states are coupled, are conspicuously present in the expression for the rate of transfer. For instance, the fluorescence quantum yield and fluorescence spectrum of the donor and the absorption spectrum of the acceptor are part of the overlap integral in the Forster rate expression, Eq. (1.2). These spectroscopic transitions are usually associated with the emission and absorption of a photon. These dipole matrix elements in the quantum mechanical expression for the rate of FRET are the same matrix elements as found for the interaction of a propagating EM field with the chromophores. However, the origin of the EM perturbation driving the energy transfer and the spectroscopic transitions are quite different. The source of this interaction term... 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

The excitation spectrum of a fluorescent material, i.e., the incident radiation spectrum required for the induction of fluorescence, is determined by the absorption spectrum of the fluorescent material, which it often closely resembles, and by the efficiency with which the absorbed energy is transformed into fluorescence. Normally, the excitation spectrum is of higher photon energy (shorter wavelength) than that of the corresponding fluorescence emission, and in sensor schemes this has an effect in the choice of preferred fluorescent agent, compatible with appropriate optical detection devices. 

The Mossbauer effect involves the resonance fluorescence of nuclear gamma radiation and can be observed during recoilless emission and absorption of radiation in solids. It can be exploited as a spectroscopic method by observing chemically dependent hyperfine interactions. The recent determination of the nuclear radius term in the isomer shift equation for shows that the isomer shift becomes more positive with increasing s electron density at the nucleus. Detailed studies of the temperature dependence of the recoil-free fraction in and labeled Sn/ show that the characteristic Mossbauer temperatures Om, are different for the two atoms. These results are typical of the kind of chemical information which can be obtained from Mossbauer spectra. 

When the frequency of a laser falls fully into an absorption band, multiple phonon processes start to appear. Leite et al 2° ) observed /7 h order ( = 1, 2. 9) Raman scattering in CdS under conditions of resonance between the laser frequency and the band gap or the associated exciton states. The scattered light spectrum shows a mixture of fluorescent emission and Raman scattering. Klein and Porto 207) associated the multiphonon resonance Raman effect with the fluorescent emission spectrum, and suggested a possible theoretical approach to this effect. 

It is a remarkable fact that the contemporary history of absorption and emission spectroscopy began simultaneously, from the simultaneous discoveries that Bunsen and Kirchhoff made in the middle of the 19th century. They observed atomic emission and absorption lines whose wavelengths exactly coincided. Stokes and Kirchhoff applied this discovery to the explanation of the Fraunhofer spectra. Nearly at the same time approximately 150 years ago, Stokes explained the conversion of absorbed ultraviolet light into emitted blue light and introduced the term fluorescence. Apparently, the discovery of the Stokes shift marked the birth of luminescence as a science. 

Absorption, Fluorescence Emission, and Photophysics of Squaraines Kock-Yee Law... 

Figure 16.34. (a) Intensity of fluorescence emission as a function of concentration for samples without superimposition between emission and absorption spectra, (b) Intensity of fluorescence emission as a function of concentration for the case where the samples present absorption in the region of emission. 

Fig. 25. Angle between emission and absorption dipole in nanosecond fluorescence measurements versus solubilized water (w0 = IHjOJ/IAOT]). [J. Colloid Interface Sci. 65, 131 (1978)1...

Zhadin NN, Alfano RR. Correction of the internal absorption effect in fluorescence emission and excitation spectra from ahsorhing and highly scattering media theory and experiment. Journal of Biomedical Optics 1998, 3, 171-186. 

In concentrated systems obtained in a thin uniform shape, the simplest way to record X-ray absorption data is the transmission mode in which the incident and transmitted photons are directly measured by means of ionisation chambers. However, in dilute systems or for surface characterisations, data are usually recorded using secondary effects resulting from the creation of the core hole during the absorption process and from its subsequent relaxation by radiative or non-radiative decays. These processes are the X-ray fluorescence emission and the total electron yield (TEY) emission, respectively. In these detection modes, the linear absorption coefficient is proportional to the ratio of the fluorescence or TEY intensity to... 

Perylenediimides represent another class of photoactive dyes which are characterized by their strong fluorescence emission and facile electrochemical reduction. Recently, a supramolecular bis(phthalocyanine)-perylenediimide hetero-triad (compound 42) has been assembled through axial coordination [47]. Treatment of perylenediimide 43, which has two 4-pyridyl substituents at the imido positions, with 2.5 equiv. of ruthenium(II) phthalocyanine 44 in chloroform affords 42 in 68% yield (Scheme 3). This array shows remarkable stability in solution due to the robustness of the ruthenium-pyridyl bond. Its electronic absorption spectrum is essentially the sum of the spectra of its molecular components 43 and 44 in... 

---