Circularly polarized fluorescence

Figure 9.29 Two-photon fluorescence excitation spectrum of 1,4-difluorobenzene. The upper and lower traces are obtained with plane and circularly polarized radiation, respectively, but the differences are not considered here. (Reproduced, with permission, Ifom Robey, M. J. and Schlag, E. W., Chem. Phys., 30, 9, 1978)...

H Shi, BM Conger, D Katsis, and SH Chen, Circularly polarized fluorescence from chiral nematic liquid crystalline films theory and experiment, Liq. Cryst., 24 163-172, 1998. 

AY Bobrovski, NI Boiko, VP Shibaev, and JH Wendorff, Cholesteric mixtures with photochemi-cally tunable, circularly polarized fluorescence, Adv. Mater., 15 282-287, 2003. 

M Voigt, M Chambers, and M Grell, On the circular polarization of fluorescence from dyes dissolved in chiral nematic liquid crystals, Chem. Phys. Lett., 347 173-177, 2001. 

Schippers and Dekkers reported on the CD and circularly polarized fluorescence of 4,4-dideuterio-adamantan-2-one (85)193. The CD of 85 originates in transitions to a totally symmetric n -+ n excited state with double minimum potential in the C=0 out-of-plane bending mode. 

The optically active 1,2-dioxetane of 2,4-adamantanedione (89) was synthesized. Thermal activation of 89 yielded chemiluminescence (Xmax = 420 nm characteristic of ketone fluorescence), pointing to intermediate 90 which is chiral only in its excited state due to the out-of-plane geometry of one of the two carbonyl groups. However, circular polarization of chemiluminescence measurement of 90 has not detected optical activity at the moment of emission. The authors have concluded that fast, relative to the lifetime of ketone singlet excited state, intramolecular n, it energy transfer caused racemization of 90196. 

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. 

Analogous g-values may be defined for the degree of circular polarization in emission [or circularly polarized photoluminescence (CPPL)] and circularly polarized electroluminescence (CPEL), eg. gCppL = 2(JL - 1R)/(1L + 1r), where IL and IR denote the intensity of left- and right-handed circularly polarized emission, respectively. CPPL should not be confused with fluorescence-detected CD. 

Fig. 2.6. Geometry for the calculation of the degree of circularity of fluorescence C at excitation by lefthanded circularly polarized light.

A similar analysis of expected signals can be performed in the case of circularly polarized excitation. If we observe the circularly polarized fluorescence in the xy plane, the righthanded Ir and lefthanded // polarized fluorescence components can be written in accordance with (2.24), and in... 

Fig. 5.4. Calculated fluorescence circularity rate under linear polarized excitation as dependent on squared electric field 2 for different absorption and fluorescence branches.

Schessinger, J., Steinberg, I. L., Givol, D., Hochmann, J., and Pecht, I., Antigen-induced conformational changes in antibodies and their Fab fragments studied by circular polarization of fluorescence. Proc. Natl. Acad. Sci. U.S.A. 72, 2775-2779 (1975). 

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)... 

Similarities between CD and absorbance extend to CD and fluorescence (FDCD) and circularly polarized luminescence (CDL) detection as well [13,14]. Chiral fluorophores can be both natural and induced. The former are considerably fewer in number because of the fact that three prerequisites are necessary to create CD fluorescence activity. Because CD signals are inherently small, and even smaller for induced forms, the higher emission signals normally associated with fluorescence are attractive to use for the... 

Scheme 2 is the simplest but not the only reaction scheme conceivable. The deactivation of, say, S may proceed via an excimer (SS) or a diastereomeric exciplex (SR). The same deactivation pattern holds, of course, for R, so that the deactivation in toto is nonasymmetric. If there were exciplex emission, circularly polarized fluorescence might be observed. Inoue discusses also a hot ground state path of deactivation [37]. 

The J sublevels of rare earths are split by ligand fields of low symmetry. These splittings may be observed in circularly polarized luminescence (CPL) but not in the fluorescence spectrum. Hence CPL spectra provide information on the rare earth ion and thus throw light on the binding site. The emission and CPL spectra of Tb3+ bound to transferrin and cobalbumin were found to be similar leading to the conclusion that the structure and... 

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