I attach some rough notes on Hush-Marcus electron transfer theory, which I have referred to in a few previous posts. I think contains very important concepts and equations that are very relevant to many biomolecular processes and issues in organic electronics and photonics.
A few points I stress:
This theoretical formalism does not just apply to electron transfer but also many other processes involving transitions between two weakly coupled quantum states which are strongly coupled to an environment which can be treated classically. (The result can be derived from a spin-boson model)
A key physical quantity is the reorganisation energy.
The Marcus inverted parabola shows that the process occurs at the greatest rate, not when the two states are at the same energy, but rather when their energy separation equals the reorganisation energy. (i.e, how much the energy of the environment changes as a result of the process).
The matrix element coupling the two states (e.g, donor and acceptor molecules) falls off exponentially with increasing spatial separation. As a result, I think charge transfer won't be fast enough for many desired processes (e.g, charge separation in organic bulk heterojunction solar cells) unless there is pi-stacking of molecules. Sulfur atoms (as in thiophenes) are also desirable for this reason.