Energy continued excitation

During the course of these studies, it was found that fluorescence intensity from the polymeric films rapidly decreased on continued excitation in a fluorescence spectrophotometer (ca. 30% loss in 1 min for L). Herein, we (1) elaborate further upon the fluorescence loss studies, (2) provide direct evidence for RET from fluorescence lifetime measurements, and (3) present preliminary findings on the photochemistry of model compounds for polymer 1. The results support the conclusion, from previous studies, that the effectiveness of added stabilizer decreases with time due to formation of a photoproduct(s) from the polymer which competes in RET, and is less able to dissipate the resulting excitation energy.1... 

It is of some importance to note that on spectral plates taken using continuous excitation the emissions from the 5Z)1 level are extremely faint. As Bhaumik points out, the time-resolved spectral technique is of great value in energy-transfer studies and is also useful at times in obtaining spectra of short-lived states whose emissions would normally be obscured by other more intense fluorescences. Clearly, it is of value in ascertaining the particular state from which a group of lines originates. 

Elkana et al. [138] made a careful study of the transfer of energy from excited naphthalene donor molecules to anthranilic acid acceptor molecules by observing the acceptor and donor fluorescence intensities when the donor was excited with continuous radiation (A = 272nm). The solvents were changed from glycerol to increasingly more and more... 

Shortly thereafter, Bouteiller continued on this same line of reasoning and considered combination bands and intensities. The data in Table 3.69 represent transitions of some combination of the v(FH) and v(P-N) bands, as indicated. At both the SCF or MP2 levels, inclusion of BSSE corrections reduce the transition energies for excitation of the v(F N) mode from the ground state ]00> 0n>, as may be seen from the first four rows of Table... 

Fluorescence Polarization under continuous excitation are presently developed. But these experiments need the a priori choice of a model of motion to be interpreted, and such models do not exist so far for the local dynamics in bulk polymers. This limitation is very troublesome, since experiments carried out on polymers in solution have shown that varying the choice of the model used in data treatment could lead to important discrepancies in the derived correlation times or activation energies. In the following, we will show how Fluorescence Anisotropy Decay may help to overcome this difficulty, and we will give some examples of original information that can be obtained using this technique in conjunction with the powerful synchrotron light source. 

---