Dexter electron transfer (also called Dexter electron exchange and Dexter energy transfer) is a

fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...

quenching mechanism in which an excited

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

is transferred from one

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

donor A donor in general is a person, organization or government which donates something voluntarily. The term is usually used to represent a form of pure altruism, but is sometimes used when the payment for a service is recognized by all parties as re ...

) to a second molecule (an

acceptor Acceptor may refer to: * Acceptor (accounting), the addressee of a bill of exchange * In the Indian Contract Act of 1872, the acceptor is the person to whom a proposal is made, and who has communicated his or her acceptance of the said proposal * ...

) via a non radiative path. This process requires a

wavefunction In quantum physics, a wave function (or wavefunction) is a mathematical description of the quantum state of an isolated quantum system. The most common symbols for a wave function are the Greek letters and (lower-case and capital psi (letter) ...

overlap between the donor and acceptor, which means it can only occur at short distances; typically within 10 Å (1 nm). The excited state may be exchanged in a single step, or in two separate charge exchange steps.

History

This short range energy transfer process was first theoretically proposed by D. L. Dexter in 1953.

Rate expression

The Dexter energy transfer rate,

k_

, is indicated by the formula: :

k_ = K J' \mathrm\left \frac \right

where

r

is the separation of the donor from the acceptor,

L

is the sum of the

Van der Waals radii The van der Waals radius, ''r'', of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom. It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, ...

of the donor and the acceptor, and

J'

is the normalized spectral overlap integral, where normalized means that both emission intensity and extinction coefficient have been adjusted to unit area. It is important noticed that

J'

, because it is normalized, does not depend on the actual magnitude of extinction coefficient nor on the donor fluorescence quantum yield. This difference is an important distinction from the situation for dipole-dipole energy transfer. The overlap integral

J'

simply derives from the density of degenerate states that couple donor and acceptor (from

Fermi's golden rule In quantum physics, Fermi's golden rule is a formula that describes the transition rate (the probability of a transition per unit time) from one energy eigenstate of a quantum system to a group of energy eigenstates in a continuum, as a result of a ...

), i.e. is a measure of the number of states that are capable of satisfying the resonance condition. Because

K

is a constant that is not related to any spectroscopic data, it is difficult to characterize the exchange mechanism experimentally.

References

Atomic physics Fluorescence {{spectroscopy-stub Energy transfer

History

Rate expression

See also

References