For photoinduced electron transfer between an acceptor ($\text{A}$) and a donor ($\text{D}$) (either one of them may be the electronically excited molecular entity) of any charge type, $z(\text{A})$ and $z(\text{D})$, the change in standard Gibbs energy can be approximated as (the notation is for the case of neutral species $\text{D}$ and $\text{A}$) $${\mathrm{\Delta }}_{\text{ET}}{G}^{\text{o}}=N_{\text{A}}\{e[E^{\text{o}}({\text{D}}^{+\bullet }/\text{D})-E^{\text{o}}(\text{A}/{\text{A}}^{-\bullet })]+w({\text{D}}^{+\bullet }{\text{A}}^{-\bullet })-w(\text{DA})\}-\mathrm{\Delta }{E}_{0,0}$$ where $e=1.602176487\times {10}^{-19}\text{C}$ is the elementary charge, $N_{\mathrm{A}}=6.02214076\times {10}^{23}{\mathrm{mol}}^{-1}$ is the Avogadro constant, $E^{\text{o}}({\text{D}}^{+\bullet }/\text{D})/\text{V}$ is the standard electrode potential of the donor cation radical resulting from the electron transfer, $E^{\text{o}}(\text{A}/{\text{A}}^{-\bullet })/\text{V}$ is the standard electrode potential of the acceptor (both relative to the same reference electrode) and $\mathrm{\Delta }{E}_{0,0}/\mathrm{J}{\mathrm{mol}}^{-1}$ is the vibrational zero electronic energy of the excited partner (provided that a vibrationally equilibrated excited state at energy $E_{0,0}$ takes part in the reaction), all data referring to the same solvent. $w({\text{D}}^{+\bullet }{\text{A}}^{-\bullet })$ and $w(\text{DA})$ are the electrostatic work terms that account for the effect of Coulombic attraction in the products and reactants, respectively $$w({\text{D}}^{+\bullet }{\text{A}}^{-\bullet })/J=\frac{z({\text{D}}^{+\bullet })z({\text{A}}^{-\bullet })e^2}{4\pi {ϵ}_0{ϵ}_{r}a}$$ $$w(\text{DA})/J=\frac{z(\text{D})z(\text{A})e^2}{4\pi {ϵ}_0{ϵ}_{r}a}$$ where $a$ is the distance of the charged species after electron transfer, ${\epsilon }_r$ is the relative medium static permittivity (formerly called dielectric constant), ${\epsilon }_0\approx 8.854\times {10}^{-12}{\text{C}}^2{\text{J}}^{-1}{\text{m}}^{-1}$ is the electric constant (vacuum permittivity), and $z(\text{X})$ the charge of the species $X$. In SI units the factor $\frac{e^2}{4\pi {\epsilon }_0}=2.307\times {10}^{-28}\text{J m}$. For the case of neutral species $\text{A}$ and $\text{D}$, $z(\text{D})=z(\text{A})=0$.