protonated dansyl units; (vi) in the case of Yb^3 þ, the sensitization
of the near-infrared MC emission occurs via the intermediate for-
mation of a dansyl to Yb^3 þ electron-transfer excited state; at
77 K the electron-transfer excited state moves to higher energy,
thus preventing the population of the Yb^3 þ emitting excited
state; (vii) the small quenching effect observed for Tb^3 þis partly
caused by a direct energy transfer from the fluorescent (S 1 )
excited state of dansyl; on protonation of the dansyl units, a
strong Tb^3 þsensitized emission is observed at 77 K, originating
from theT 1 excited state of the protonated dansyl units.
An extension of the present work has recently been published
( 30 ), in which a supramolecular system constituted by five lumi-
nescent components, namely, one dendrimer 3 , two Nd^3 þ ions,
and two molecular clips, have been assembled in solution with
light-harvesting properties.
A.2. Amine coordinating units
Dendrimers of the poly(propylene amine) family can be easily
functionalized in the periphery with luminescent units such as
dansyl ( 31 ). The resulting dendrimersnD, where the generation
numberngoes from 1 to 5, comprise 2(nþ1)dansyl functions in
the periphery and 2(nþ1)2 tertiary amine units in the interior.
Gd3+(^6) P7/2
Eu3+
(^5) D 0
Tb3+ Nd3+
(^5) D 4
(^8) S
(^7) Fj^4 Ij^7 Fj
(^4) F3/2
(^2) F5/2
(^2) F7/2
Yb3+
(^4) I15/2
(^4) I13/2
Er3+
T 1 (?)
S 1
15
10
5
20
E (10
3 cm
–1
)
30
25
0 S 0
3
FIG. 8. Energy level diagrams for the dansyl units of dendrimer 3
and the investigated lanthanide ions. The position of the triplet excited
state of 3 is uncertain because no phosphorescence can be observed.
120 VINCENZO BALZANIet al.