What is the Difference Between Excimer and Exciplex

Madhu

2 years ago

The key difference between excimer and exciplex is that excimer has two species, whereas exciplex has more than two species.

1. Overview and Key Difference
2. What is an Excimer
3. What is an Exciplex
4. Excimer vs Exciplex in Tabular Form
6. Summary – Excimer vs Exciplex

What is an Excimer?

An excimer can be described as a short-lived dimeric or heterodimeric molecule that forms from two species where at least one species has a valence shell with a completed electron configuration. The term excimer stands for “excited dimer.” Often, excimers are diatomic, and these consist of two atoms or molecules that do not bind if both species are in the ground state.

Typically, the lifetime of an excimer is very short, and it is measured on the nanoseconds scale. Moreover, if a large number of excited atoms are bonded, it forms Rydberg matter clusters, and its lifetime can increase by many seconds.

When considering the formation of this state, a typical ground-state molecule has electrons in the lowest possible energy level; at most, only two electrons occupy a given orbital where two electrons are of opposite spin states. HOMO is the highest occupied molecular orbital, while LUMO is the lowest unoccupied molecular orbital. These two orbitals have an energy gap, and the absorption of light with the same energy as of the energy gap can cause the formation of a molecule’s excited state. An excimer is formed when the dimer components are in the excited state.

What is an Exciplex?

Exciplex is a short-lived molecule in the excited state that is formed from more than two species. Therefore, it is an excited state complex that forms between a molecule that donates electrons and one that accepts electrons.

Generally, these complexes are of interest for the favorable light-emission properties they have. We can understand exciplex emission from potential energy diagrams of exciplex-forming species. An excimer is also a type of exciplex and contains only two species forming the complex molecule.

Since there are more than two monomers in an exciplex, it is highly unstable and has a very short-lived nature compared to other types of excited states such as excimers.

What is the Difference Between Excimer and Exciplex?

An excimer can be described as a short-lived dimeric or heterodimeric molecule that forms from two species where at least one species has a valence shell with a completed electron configuration. Exciplex is a short-lived molecule in the excited state that is formed from more than two species. The key difference between excimer and exciplex is that excimer has two species, whereas exciplex has more than two species.

The below infographic presents the differences between excimer and exciplex in tabular form for side-by-side comparison.

Summary – Excimer vs Exciplex

Exciplex and excimer are excited states of some chemical reactions in organic chemistry. An excimer is a short-lived dimeric or heterodimeric molecule that forms from two species where at least one species has a valence shell with a completed electron configuration. Exciplex is a short-lived molecule in an excited state that is formed from more than two species. The key difference between excimer and exciplex is that excimer has two species, whereas exciplex has more than two species.

Reference:

1. “Exciplex Formation.” An Overview | ScienceDirect Topics.
2. “What Is an Excimer Laser?” TWI.

Image Courtesy:

1. “Excimer energy diagram” By Excimer_energy-diagram.gif: The original uploader was Tomgally at English Wikipedia.derivative work: Rehua – This file was derived from: Excimer energy-diagram.gif: (Public Domain) via Commons Wikimedia
2. “LCU Spacetime Exciplex” By Copernicus01 – Drawn and redrawn over past year using Windows Paint program: Previously published: used in PowerPoint presentations etc. (CC BY-SA 3.0) via Commons Wikimedia

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