What should the Rehm-Weller equation look like? The Rehm-Weller equation, which defines the energy change for photoinduced electron transfer according to Lakowicz &quot;Principles of Fluorescence Spectroscopy&quot; [1, p. 337] should look like:
$$\Delta G=E^\mathrm{red}(D^+/D)-E^\mathrm{red}(A/A^-)-\Delta G_{00} - \frac{e^2}{\epsilon d} \tag{1}$$
So you can see the first two components are reduction potentials of donor $D^+$ and acceptor $A$. But sometimes you can find another definition:
$$\Delta G=E^\mathrm{ox}(D/D^+)-E^\mathrm{red}(A/A^-)-\Delta G_{00} - \dfrac{e^2}{\epsilon d} \tag{2}$$
Which one is correct? I'm totally confused.
References

Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3rd ed.; Springer: New York, 2006. ISBN 978-0-387-31278-1.
Both expressions are identical. It's just juggling of the signs, since

$$E^{\mathrm{red}}(D^{\cdot+}/D) = - E^{\mathrm{ox}}(D/D^{\cdot+})$$

Relevant primary references would be:


Rehm, D.; Weller, A. H. Isr. J. Chem. 1970, 8, 259-271.
Rehm, D.; Weller, A. H. Ber. Bunsen-Ges. Phys. Chem. 1969, 73,
834-839.
Weller, A. H. Z. Phys. Chem. NF 1982, 133, 93-98.


A normative glossary of terms in photochemistry is available from the IUPAC.