Polarization of luminescence

In addition to ORD and CD, the optical activity of a dissymmetric molecule is manifested in an additional spectroscopic property if the molecule is luminescent. Circular polarization of luminescence (CPL) 

The CPL of various cyclic dipeptides containing tryptophan residues has been studied (346). The optical rotatory power deduced from these measurements vanished upon electronic excitation in fluid media but is essentially the same in the ground and electronically excited states in highly viscous media. A change in conformation thus occurs upon excitation in fluid solution essentially before light emission takes place. The change responsible for the disappearance of the optical activity is faster than the rate of rotational relaxation as monitored by the 

In a preliminary communication Turner et al 409) reported that the signal-to-noise ratios in lysozyme CPL spectrum is several times larger than for L-tryptophan spectrum. This was not unexpected since one can find an analogous behaviour in the corresponding CD spectra. 

A CPL study indicated that the conformation of the indole side chain of the single tryptophan residue of staphyloccocal nuclease and its interaction with the environment is very similar in the ground state and in its first singlet excited state 381). Also the environment of the tryptophan residue is not affected noticeably by the binding of calcium ions that are known to be necessary for the activity of this enzyme. 

In marked contrast to the behaviour of staphylococcal nuclease and azurin, which also has its emission anisotropy factor nearly constant across the emission band, the CPL properties of human serum albumin reflect a heterogeneity in the population of the molecules of this protein, different molecules having different emission spectra and different dissymmetric environments for their single tryptophan residue 381). 

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Other methods150 involve isotopic dilution,151 kinetic resolution,152 13C nmr relaxation rates of diastereomeric complexes,153 and circular polarization of luminescence.154... 

Direct asymmetric cpl-induced photoreactions are only observed if there are two enantiomeric ground state reactants presgntthat absorb different amounts of light. Thus the asymmetry of the cpl source is transformed into a different concentration of excited-state enantiomeric species, which becomes obvious in emitting systems in the circular polarization of luminescence [7]. These in turn react in a nonchiral environment with the same rate constants for the different deactivation channels. Thus asymmetric photoreactions are dependent or independent parallel reactions of the enantiomers with different net rates. 

The results of the theoretical analysis in Sect. 1.2 show that in the study of relaxation processes in solutions of polymers containing luminescent markers (LM) much information is provided by the dependence of the reciprocal value of the polarization of luminescent light of the polymer solution, 1/p, on the viscosity of the solvent tj, 1/p =/(T/t ), measured at constant temperature T. Theoretical analysis of Eq. (1.2.10) shows that for macromolecules in solution in which all the relaxation processes occur at times Tj >Tf (t/ is the lifetime of luminescence) the following equation is valid for the average time r i (see Sect. 1.2) (Eq. 2.1) 1... 

The investigation of the intramolecular mobility (I MM) of macromolecules by the method of polarized luminescence (PL) is based on the study of the characteristics of luminescent light (polarization of luminescence and lifetime in the excited state) of luminescent groups bonded to the investigated macromolecules. 

It was necessary to carry out systematic investigations of the polarization of the luminescence of groups bonded to macromolecules and of its relationship to the peculiarities of the IMM of polymers of various structure. Hence, it was necessary to develop various methods for the synthesis of labeled polymers differing not only in the structure but also in the content and arrangement of LM in macromolecules (in side groups, in the main chain or at its end). Studies on the polarization of luminescence of LM with different locations in macromolecules permit to determine the dynamic characteristics of various parts of the polymer chain. 

Brace, J.L Dickins, R.S. Govenlock, L.J. Gunnlaugsson. T. Lopinski. S. Lowe. M.P. Parker. D. Peaeoek. R.D. Perry. J.J.B. Aime, S. Botta. M. The seleetivity of reversible oxy-anion binding in aqueous solution at a chiral europium and terbium center Signaling of earbonate chelation by changes in the form and eireular polarization of luminescence emission. J. Am. Chem. Soc. 2000, 122 (40), 9674-9684. 

Scharmann A, Schwabe D Polarization of luminescence of cubic ZnS Mn single crystals. Physica Status Solidi B-Basic Research 1974, 63(2) 535-544. 

The value of Pq is the limiting value of the polarization of luminescence observed when the Brownian motion is frozen, e.g. in very viscous media in which (r/i ) -> 0 (where t is the viscosity of the solvent and T the absolute temperature " . This value is determined by the chemical structure of the luminescent maaomolecule and the mutual arrangement of emitting and absorbii oscillators " ... 

Steinberg IZ, Gafui A. Sensitive Instrument for the Study of Circular Polarization of Luminescence. Rev Sci Instmm 1972 43 409 13. 

Rexwinkel RB, Schakel P, Meskers SCJ, Dekkers HPJM. Time-Resolved Polarization of Luminescence Spectroscopy an Accurate and Versatile Digital Instrument for the Sub-//s Time Domain. Appl Spectrosc 1993 47 (6) 731-740. 

Tinoco J, I., Ehrenberg B, Steinberg E. Eluorescence Detected Circular Dichroism and Circular Polarization of Luminescence in Rigid Media Direction Dependent Optical Activity Obtained by Photoselection. J Chem Phys 1977 66 916-920. 

Bruce JI, Dickins RS, Govenlock LJ, Gunnlaugsson T, Lopinski S, Lowe MP, et al. The Selectivity of Reversible Oxy-anion Binding in Aqueous Solution at a Chiral Europium and Terbium Center Signaling of Carbonate Chelation by Changes in the Form and Circular Polarization of Luminescence Emission. J Am Chem Soc 2000 122 9674-9684. 

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