Preferred Label : Gibbs energy of photoinduced electron transfer;
IUPAC definition : For photoinduced electron transfer between an acceptor (A) and a donor (D) (either
one of them may be the electronically excited molecular entity) of any charge type,
z(A) and z(D), the change in standard Gibbs energy can be approximated as (the notation
is for the case of neutral species D and A) \[Δ _{{ET}}G {{o}} N_{{A}}\left \{e\,
[E {{o}}({D} { \bullet }/{D})- E {{o}}({A}/{A} {-\bullet }) ] w({D} { \bullet }{A}
{-\bullet })-w({DA})\right \} - Δ E_{0,0}\] where e 1.602176487 x 10E-19 C is the
elementary charge, NA 6.022 141 79 x 10E23 mol-1 is the Avogadro constant, Eo(D
•/D)/V is the standard electrode potential of the donor cation radical resulting from
the electron transfer, Eo(A/A-•)/V is the standard electrode potential of the acceptor
(both relative to the same reference electrode) and ΔE0,0/J mol-1 is the vibrational
zero electronic energy of the excited partner (provided that a vibrationally equilibrated
excited state at energy E0,0 takes part in the reaction), all data referring to the
same solvent. w(D •A-•) and w(DA) are the electrostatic work terms that account for
the effect of Coulombic attraction in the products and reactants, respectively \[w({D}
{ \bullet }{A} {-\bullet })/J \frac{z({D} { \bullet })z({A} {-\bullet })e {2}}{4\pi
\epsilon _{0}\epsilon _{r}a}\] \[w({DA})/J \frac{z({D})z({A})e {2}}{4\pi \epsilon
_{0}\epsilon _{r}a}\] where a is the distance of the charged species after electron
transfer, ɛr is the relative medium static permittivity (formerly called dielectric
constant), ɛ0 8.854 x 10E-12 C2 J-1 m-1 is the electric constant (vacuum permittivity),
and z(X) the charge of the species X. In SI units the factor e2.4π.ɛ0 2.307 x 10E-28
J m. For the case of neutral species A and D, z(D) z(A) 0.;
Scope note : the equation used for the calculation of the gibbs energy of photoinduced electron-transfer
processes should not be called the rehm-weller equation.; the standard emfs of oxidation and reduction are often called, respectively, oxidation
and reduction potential. these terms are intrinsically confusing and should be avoided
altogether, because they conflate the chemical concept of reaction with the physical
concept of electrical potential.; in the above definitions, the iupac recommendations for the sign and symbols of standard
potentials are used. although not complying with the iupac-recommended nomenclature
for the standard electrode potentials, traditionally the equation has been written
as: detg o na e
eoxo eredo za zd 1
e2 4p ¿0 ¿ r a de0,0
with eoxo the standard electrode potential at which the oxidation occurs, and
eredo the standard electrode potential at which the reduction occurs. this form
of the first term within the brackets is misleading and not recommended.; several approximations are in use for the calculation of the term w
d •a-• , depending on the nature of the species formed such as contact or solvent-separated
radical ion pairs or extended and/or linkeddanda molecular entities. in the latter
case, the stabilization of a dipole µ in a cavity of radius ? could
be an appropriate model and w d •a-•
na µ2 4p ¿0 ?3 ¿ r 1
2¿ r 1;
Origin ID : GT07388;
See also
For photoinduced electron transfer between an acceptor (A) and a donor (D) (either
one of them may be the electronically excited molecular entity) of any charge type,
z(A) and z(D), the change in standard Gibbs energy can be approximated as (the notation
is for the case of neutral species D and A) \[Δ _{{ET}}G {{o}} N_{{A}}\left \{e\,
[E {{o}}({D} { \bullet }/{D})- E {{o}}({A}/{A} {-\bullet }) ] w({D} { \bullet }{A}
{-\bullet })-w({DA})\right \} - Δ E_{0,0}\] where e 1.602176487 x 10E-19 C is the
elementary charge, NA 6.022 141 79 x 10E23 mol-1 is the Avogadro constant, Eo(D
•/D)/V is the standard electrode potential of the donor cation radical resulting from
the electron transfer, Eo(A/A-•)/V is the standard electrode potential of the acceptor
(both relative to the same reference electrode) and ΔE0,0/J mol-1 is the vibrational
zero electronic energy of the excited partner (provided that a vibrationally equilibrated
excited state at energy E0,0 takes part in the reaction), all data referring to the
same solvent. w(D •A-•) and w(DA) are the electrostatic work terms that account for
the effect of Coulombic attraction in the products and reactants, respectively \[w({D}
{ \bullet }{A} {-\bullet })/J \frac{z({D} { \bullet })z({A} {-\bullet })e {2}}{4\pi
\epsilon _{0}\epsilon _{r}a}\] \[w({DA})/J \frac{z({D})z({A})e {2}}{4\pi \epsilon
_{0}\epsilon _{r}a}\] where a is the distance of the charged species after electron
transfer, ɛr is the relative medium static permittivity (formerly called dielectric
constant), ɛ0 8.854 x 10E-12 C2 J-1 m-1 is the electric constant (vacuum permittivity),
and z(X) the charge of the species X. In SI units the factor e2.4π.ɛ0 2.307 x 10E-28
J m. For the case of neutral species A and D, z(D) z(A) 0.
