Chemistry Reference
In-Depth Information
increases with dendrimer generation (Table 11.3), but the corresponding values are
quite close and too small for the larger dendrimers. For example, in the case of G4
a
radius of 1.6 nm is estimated by the corresponding hydrodynamic volume, while
molecular model suggest a more expanded structure (radius about 2 nm) [21]. These
results indicate that this family of dendrimers may not be considered as simple
spherical rotors. Indeed, as evidenced by steady-state measurements, the local motion
is an additional process that contributes to depolarize fluorescence and shorten
rotational relaxation times.
Time-dependent data are not presented in dichloromethane/propylene glycol
mixtures since in this solvent mixture a biexponential decay of fluorescence intensity
is observed, which prevents fitting of the corresponding anisotropy decays.
D
11.3.2 Dendrimer with Stilbenyl Units at the Periphery
SimilarlytotheGn
D
family, the poly(propylene amine) dendrimer G2
S
contains
identical fluorescent units (in this case, stilbenyl units
S
) appended in the periphery
(Scheme 11.6) [24]. Therefore, also for G2
depolarization can in principle occur
by (i) global rotation of the dendrimer, (ii) local motions of the peripheral
S
SO
2
SO
2
N
N
SO
2
N
N
N
N
O
2
NN
O
2
S
N
N
N
N
O
2
S
N
SO
2
N
N
O
2
S
O
2
S
S
G2
S
SCHEME 11.6
Second-generation poly(propylene amine) dendrimer with stilbenyl
S
peripheral units.
