inorganic chemistry

When an excited state of a molecule undergoes strong elec-

tronic interaction with a nearby ground state molecule, new

chemical species originate, which are called excimers (from

excited dimers) or exciplexes (fromexcited complexes), depending

on whether the two interacting units have the same or different

chemical nature (Fig. 4a). It is important to notice that excimer

and exciplex formation is a reversible process and that both

excimers and exciplexes sometimes (but not always!) can give

luminescence (Fig. 4b). Compared with the“monomer”emission,

the emission of an excimer or exciplex is always displaced to

lower energy (longer wavelengths) and usually corresponds to a

broad and rather weak band.

Excimers are usually obtained when an excited state of an aro-

matic molecule interacts with the ground state of a molecule of

the same type. Exciplexes are obtained when an electron donor

(acceptor) excited state interacts with an electron acceptor

Exciplex

interaction

Excimer

interaction

B

(a)

(b)

A

*A

A-*A-B

A-A-B

hν′

hν

hν′′

*[A-A]-B

excimer

A-*[A-B]

exciplex

FIG. 4. Schematic (a) representation of excimer and exciplex forma-
tion in a dendrimer and (b) energy level diagram showing the three
types of emissions that can result.

112 VINCENZO BALZANIet al.