6 Excimers and Exciplexes
Excimers (and exciplexes) are emissive metastable species [65–67] (MSS) that are
electronically aggregated dimeric entities in the excited state whose chromophores
remain dissociated otherwise. Electronic interaction between an excited chromophore M
* and a ground-state chromophore M leads to an aggregated species
(M*. . .M), which is referred to as the excimer (E
* , Fig. 22). Homochemical
Acceptor
Donor
Biphenyl bipyridinium (BP)
A
D
D
A
D
D
2.34 eV
LE
0.00 eV
GS
1.92 eV TICT
0.28 eV
MSS
λ
abs
λ
em
λ
abs
λ
em
Fig. 20 (Top) Structure of the BP fluorophore. (Bottom) Conformational change between nearplanar LE and near-orthogonal TICT states and their relative energies. Details reproduced from
published work [64]
Fig. 21 Complexation equilibria of biphenyl/bipyridinium TICT fluorophores and difference in
their emissions controlled supramolecularly. The emission spectra are that for BP complexed to
CB8 (purple), CB7(blue), and β-CD (red), respectively. Structures and spectra reproduced from
published work [64]
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