What is the Difference Between Excimer and Exciplex?

Excimers and exciplexes are both short-lived species generated in the excited state of certain chemical reactions in organic chemistry. They dissociate in the ground state. The key difference between an excimer and an exciplex is the number of species involved in their formation:

• Excimer: An excimer is a short-lived dimeric or heterodimeric molecule that forms from two species, at least one of which has a valence shell completely filled with electrons. If the two monomers are of the same species, the complex is called an excimer (excited dimer).
• Exciplex: An exciplex is a short-lived molecule in an excited state that is formed from more than two species. When the two monomers are different, the complex is known as an exciplex.

Both excimers and exciplexes are generally formed in solutions due to the high likelihood of collisions. In the solid state, excimers can be formed in crystalline form through stacking, while in amorphous solids, molecules can also form excimers or exciplexes. Exciplexes are useful as thermally activated delayed fluorescence (TADF) materials due to their small triplet-singlet energy difference, making them promising for use in high-efficiency third-generation organic light-emitting diodes (OLEDs).

Comparative Table: Excimer vs Exciplex

The main difference between an excimer and an exciplex is the number of species involved in their formation. Here is a summary of their differences:

Excimers and exciplexes are both excited states in chemical reactions in organic chemistry and are highly unstable with short lifetimes. They are generally of interest for their favorable light-emission properties, which can be understood through potential energy diagrams of exciplex-forming species.