Chemistry Reference
In-Depth Information
2
before
(solid circles) and after successive additions of 1 equiv. of Zn(CF
3
SO
3
)
2
(open triangles) and 1
equiv. of
D
(open squares) in acetonitrile/dichloromethane 1:1 (v/v) solution at 298 K.
l
ex
ΒΌ
355 nm [35].
Steady-state anisotropy of a 3.5
10
6
M solution of clip
C
FIGURE 11.5
11.6 CONCLUSIONS
The dendritic systems presented in this paper, based on various luminophores located
in selected positions of the dendritic architecture, provide representative examples of
different mechanisms of fluorescent depolarization.
In the case of a single fluorophore located at the dendritic core, fluorescence
depolarization may be due to global rotation of the dendrimer in solution or to
interdendrimer energy migration in the powder. By examining rotational relaxation
times in solution, information on the hydrodynamic volume of the dendrimers and
influence of the solvent on dendron back folding are obtained.
In the case of multiple fluorescent units located at the periphery or in the branching
points of the dendrimer, mechanisms of fluorescence depolarization are: global
rotation of the macromolecule, local motion of the luminescent subunits, and energy
migration between identical chromophores. The last path should be considered or not
depending on the distance and nature of the fluorescent units. It is worth noting that
energy migration cannot be evidenced by conventional fluorescence intensity decay
since it does not lead to a quenching of the emitting excited state. Therefore,
fluorescence depolarization offers a handle to study the rate and the mechanism
(coherent or incoherent hopping) of energy migration and the average number of
chromophoric units involved in this process. This feature is particularly important in
view of studying signal amplification in dendritic luminescent sensors.
