An interesting self-assembled light-harvesting antenna system
based on a ruthenium complex and a Nd(III) emitter has been
reported by Balzaniet al.( 44 ). The three-component assembly
containing a dendrimeric 1,4,8,11-tetraazacyclotetadecane
(cyclam) core with appended 12 dimethoxybenzene and 16
naphthyl units able to harvest light in the UV region, (D), [Ru
(bpy) 2 (CN) 2 ] able to absorb light in the visible but also to coordi-
nate other metal ions, and Nd^3 þcations able to emit in the infra-
red region if suitably sensitized. The components were added in
equimolar amounts, to form the assembly {DNd^3 þ[Ru
(bpy) 2 (CN) 2 ]} ( 44 ). The cyclam core is able to coordinate the Nd
ions, but the dendrimerDis not able to directly sensitize the lan-
thanide ion located in its core. However, the organic
chromophores are able to efficiently transfer electronic energy
to the [Ru(bpy) 2 (CN) 2 ] complex, which is coordinated through
the cyano groups to the Nd. The excited Ru complex can then
emit or sensitize the line-like emission of the NdIII ion, as
observed by recording the IR emission spectrum.
Besides hydrophobic and coordinative interactions, hydrogen
bonds and electrostatic interactions have been used to assemble
luminescent metal complexes. In this context, Barigelletti and
coworkers ( 45 – 47 ) reported on the luminescent properties of
Ru(II) and Os(II) complexes containing bipyridines peripherally
functionalized with nucleotide bases, cytosine, and guanine,
OON N
N N
N NO
OΔEΔEOE in eV3.04.02.0
1.0
0.0(^1) Anth
(^3) Anth
Step c Step b^3 Os-ada
Step a
k= 1.8× 1010 s–1
(^1) Ru(a 2 b)
(^3) Ru(a 2 b)k= 0.9× 109 s–1
N
N
N N
N
N
Rull
hn
FIG. 4. Schematic formula of the multicomponent system and its
energy levels. Due to the energy cascade process, the electronic energy
can be transferred from the excited anthracene to the osmium acceptor
(green) via the ruthenium moiety ( 43 ).
PHOTOPHYSICS OF MOLECULAR ASSEMBLIES 57