B. DENDRIMERS WITH ASINGLECOORDINATIONSITE
A much better defined coordination arrangement around a
metal ion is obtained when a dendrimer contains a precise coor-
dination site, for example, in the core.
Dendrimer 5 (Fig. 11) consists of a cyclam core appended with
12 dimethoxybenzene and 16 naphthyl units. Cyclam is one of
the most extensively investigated ligands in coordination chemis-
try ( 33 ). Both cyclam and its 1,4,8,11-tetramethyl derivative in
aqueous solution can be protonated and can coordinate metal
ions such as Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) with
high stability constants ( 34 ).
In acetonitrile–dichloromethane 1:1 (v/v) solution, the absorp-
tion spectrum of dendrimer 5 is dominated by naphthalene
absorption bands and the dendrimers exhibit three types of emis-
sion bands, assigned to naphthyl-localized excited states
(lmax¼337 nm), naphthyl excimers (lmax ca. 390 nm), and
naphthyl-amine exciplexes (lmax¼480 nm)( 35 ).
Extensive investigations have been performed on the interac-
tion of dendrimers of this class with metal ions( 36 ). Coordina-
tion of Zn^2 þ, a metal ion that is difficult to oxidize and reduce
and that exhibits a d^10 electronic configuration, leads to
FIG. 11. Formula of a dendrimer consisting of a cyclam core, capable
of coordinating a Zn^2 þion, and the corresponding scheme (Fig. 2c).
PHOTOCHEMISTRY & PHOTOPHYSICS OF METAL COMPLEXES 123