Circularly polarized fluorescence spectroscopy

III. Chirality of excimers as observed with circularly polarized fluorescence spectroscopy, 203... 

III. CHIRALITY OF EXCIMERS AS OBSERVED WITH CIRCULARLY POLARIZED FLUORESCENCE SPECTROSCOPY... 

Since polypeptides are chiral polymers, the chromophore arrangement shows some chirality. Therefore, additional information on the chromophore arrangement in the ground state, as well as in the excited state, may be obtained from chiroptical spectroscopy, such as circular dichroism (CD), circularly polarized fluorescence (CPF) [43], and fluorescence-detected circular dichroism (FDCD) [44). 

One characteristic feature of excimers in the polypeptide I-O and 1-2 is that they emit circularly polarized light [43,51]. Circularly polarized fluorescence (CPF) spectroscopy measures the difference in fluorescence intensity of the left and right circularly polarized component. Usually the CPF spectrum is plotted with Kuhn s circular dissymmetry factor, as the... 

Maupin, C. L. Riehl, J. P. Circularly polarized luminescence and fluorescence detected circular dichroism. In Encyclopedia of Spectroscopy and Spectrometry, Lindon, J. C. Trantner, G. E. Holmes, J. L., Eds. Academic Press, 2000 pp 319-326. 

In FDCD spectroscopy one varies the polarization of the excitation (absorption) beam between right (r) and left (l) circular polarization while measuring the total emission intensity. When the excitation is right circularly polarized we denote the measured fluorescence intensity by Fr, and by F when the excitation is left circularly polarized. Once again, we will be concerned with the determination of the difference between these two quantities, which in this case we will denote as AF [6]. In a "steady state" experiment we may express this differential quantity as follows... 

In these equations, B is an instrumental constant <)> is the probability that an absorbed photon leads to fluorescence and A (X) and A (X) are, respectively, the absorbance of the fluorophore only, and the total absorbance under left circularly polarized excitation at wavelength X. Note that we have assumed that < > is independent of excitation polarization and wavelength. The form of eqs. (26) and (27) display one of the problems in simple interpretation of FDCD results in terms of ordinary CD spectroscopy. On the front surface of the sample cell the intensity of the alternating circular polarizations will be equal, but if Ar does not equal A then the intensities will change due to differential absorption. Just as in CPL measurements, one is concerned in this case with measurement of the differential signal and the total fluorescence intensity, F(X)... 

CPF spectroscopy measures a difference in intensities of left-and right-circularly polarized components of a fluorescence emitted from a chiral fluorophore and reflects the chirality of conformations and interactions in the excited state (2 ). Figure 1 shows CPF spectra of poly(l- and 2-napAla)s measured in DMF solution (12). The ordinate of the CPF spectra is the Kuhn s emission dissymmetry factor g, ... 

Many features of the emission spectrum can show time dependence, including the spectral shape (l,3 (v-9), the peak intensity, the linear polarization (10) and, in principle, the circular polarization (11). In extreme cases, the emission spectrum can actually have two separate fluorescence bands from two different isomers of the electronically excited molecules (12-15). For molecules with this behavior, it is possible to determine the kinetics of excited state isomerization by transient emission spectroscopy. 

There is an impressive battery of spectroscopic techniques available for probing interactions between metal complexes and DNA. The oldest of these, UV/vis spectroscopy, is still one of the most sensitive ways to analyze dye-DNA interactions. For chiral metal complexes, circular dichroism is an invaluable tool. Fluorescence spectroscopy has in particular made great strides in recent years with respect to these applications, and aside from the measurement of simple emission from an excited metal complex, one can utilize emission polarization, luminescence lifetimes, and differential fluorescence quenching to obtain still more information about the environment about a metal complex. The application of ruthenium complexes, in particular, to developing probes for DNA, has been initiated in our laboratory and we focus here on some of its applications. 

Biochemical Applications of Fluorescence Spectroscopy Biomacromolecular Applications of Circular Dichroism and ORD Biomacromolecular Applications of UV-Visible Absorption Spectroscopy Chemical Reactions Studied By Electronic Spectroscopy Circularly Polarized Luminescence and Fluorescence Detected Circular Dichroism Dyes and Indicators, Use of UV-Visible Absorption Spectroscopy... 

See also Chiroptical Spectroscopy, General Theory Chiroptical Spectroscopy, Oriented Molecules and Anisotropic Systems Circularly Polarized Luminescence and Fluorescence Detected Circular Dichr-oism Luminescence, Theory. 

Circularly Polarized Luminescence and Fluorescence Detected Circular Dichroism Induced Circular Dichr-oism Magnetic Circular Dichroism, Theory ORD and Polarimetry Instruments Rotational Spectroscopy, Theory Vibrational CD Spectrometers Vibrational CD, Applications Vibrational CD, Theory. 

The differential emission of left and right circularly polarized light from luminescent molecular systems is called circularly polarized luminescence (CPL), and is at the basis of the corresponding spectroscopic technique (CPL spectroscopy) [23-25]. CPL spectroscopy should not be confused with fluorescence detected circular dichroism (see Sect. 6.1.6) in the latter technique the differential absorption of the circularly polarized components is detected through fluorescence measurements, owing to the different extent of photoexcitation that left- and right-handed light can produce on a chiral molecule. 

Maupin CL, Riehl JP. Circularly Polarized Luminescence and Fluorescence Detected Circular Dichroism. In Lindon JC, Trantner GE, Holmes JL, editors. Encyclopedia of Spectroscopy and Spectrometry Academic Press, New York 2000, pp. 319-326. 

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