Time resolved fluorescence theoretical modeling studies

Time-resolved emission anisotropy experiments provide information not only on the fluidity via the correlation time rc, but also on the order of the medium via the ratio rco/ro. The theoretical aspects are presented in Section 5.5.2, with special attention to the wobble-in-cone model (Kinosita et al., 1977 Lipari and Szabo, 1980). Phospholipid vesicles and natural membranes have been extensively studied by time-resolved fluorescence anisotropy. An illustration is given in Box 8.3. 

The above described model sequences have been studied both as oligomers [7,8,11-13,19] and as polymers [9,11,20]. An increase in the size of the helix is known to reinforce its stability, as revealed by their melting curves [18] and attested by X-ray diffraction measurements in solution [21]. Therefore, in this chapter we focus on the polymeric duplexes poly(dGdC).poly(dGdC) [= 1000 base-pairs], poly(dAdT).poly(dAdT) [= 200-400 base-pairs] and poly(dA).poly(dT) [= 2000 base-pairs] studied by us. First we discuss the absorption spectra, which reflect the properties of Franck-Condon states, in connection with theoretical studies. Then we turn to fluorescence properties fluorescence intensity decays (hereafter called simply fluorescence decays ), fluorescence anisotropy decays and time-resolved fluorescence spectra. We... 

While useful as a simple, model case with which one can demonstrate many of the principles involved in vibrational coherence, IVR between two vibrational levels is clearly not a very general situation. In view of the expectation that vibrational coupling in molecules may involve any number of levels and that many such cases of multilevel IVR are amenable to study by picosecond spectroscopy, it is useful to have theoretical guidelines301 pertaining to the manifestations that a system of N coupled vibrational levels might exhibit in time-resolved fluorescence. Hence, we consider now the situation depicted in Fig. 2. 

The time and wavelength resolved fluorescence dynamics of bianthryl has been investigated by several groups [30, 82, 132, 133, 115, 116]. In addition, this molecule has been studied by picosecond absorption spectroscopy [115], electric field induced fluorescence anisotropy measurements [117] and optically induced dielectric absorption (microwave) measurements [118, 119]. The results are generally in accord with the theoretical model presented in Sections III.A and III.B. One of the challenges of studying the photodynamics of BA is that the LE and CT interconversion is so rapid (i.e., on the time scale of solvation) that it is necessary to employ ultraviolet subpicosecond and even femtosecond fluorescence spectroscopy which has only recently become available [30, 82, 132, 133]. 

---