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Triplet-triplet annihilation (TTA) is an energy transfer mechanism between two molecules in their
Triplet-triplet annihilation (TTA) is an energy transfer mechanism between two molecules in their triplet
A triplet is a set of three items, which may be in a specific order, or unordered. It may refer to:
Science
* A series of three nucleotide bases forming an element of the Genetic code
* J-coupling as part of Nuclear magnetic resonance spectrosc ...
state,Turro, Nicholas J., Ramamurthy, V., Scaiano, J.C. (2010) ''Modern Molecular Photochemistry of Organic Molecules'', University Science Books, and is related to the Dexter energy transfer mechanism. If triplet-triplet annihilation occurs between two molecules in their excited state
In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers to a ...
s one molecule transfers its excited state energy to the second molecule, resulting in one molecule returning to its ground state and the second molecule being promoted to a higher excited singlet, triplet
A triplet is a set of three items, which may be in a specific order, or unordered. It may refer to:
Science
* A series of three nucleotide bases forming an element of the Genetic code
* J-coupling as part of Nuclear magnetic resonance spectrosc ...
or quintet
A quintet is a group containing five members. It is commonly associated with musical groups, such as a string quintet, or a group of five singers, but can be applied to any situation where five similar or related objects are considered a single ...
state.
Triplet-triplet annihilation was first discovered in the 1960s to explain the observation of delayed fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
in anthracene
Anthracene is a solid polycyclic aromatic hydrocarbon (PAH) of formula C14H10, consisting of three fused benzene rings. It is a component of coal tar. Anthracene is used in the Economic production, production of the red dye alizarin and other dyes ...
derivatives.
Photon upconversion
As triplet-triplet annihilation combines the energy of two triplet excited molecules onto one molecule to produce a higher excited state it has been used to convert the energy of two photons into one photon of higher energy, a process known asphoton upconversion
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always m ...
.
To achieve photon upconversion through triplet-triplet annihilation two types of molecules are often combined: a sensitizer and an emitter (annihilator). The sensitizer absorbs the low energy photon and populates its first excited triplet state (T1) through intersystem crossing Intersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different spin multiplicity.
Excited Singlet and Triplet States
When an electron in a molecule with a singlet ground ...
. The sensitizer then transfers the excitation energy to the emitter, resulting in a triplet excited emitter and a ground state sensitizer. Two triplet excited emitters then can undergo triplet-triplet annihilation, and if a singlet excited state (S1) of the emitter is populated fluorescence results in an upconverted photon.
References
{{reflist Spectroscopy Atomic physics