  Photochromic molecular structures constitute a unique platform for
constructing molecular switches, sensors and memory devices. One of their most
promising applications is as light-switchable electron acceptor or donor units.
Here, we investigate a previously unexplored process that we postulate may
occur in such systems: an ultrafast electron transfer triggered by a
simultaneous photoisomerization of the donor or the acceptor moiety. We propose
a theoretical model for this phenomenon and, with the aid of DFT calculations,
apply it to the case of a dihydropyrene-type photochromic molecular donor. By
considering the wavepacket dynamics and the photoisomerization yield, we show
that the two processes involved, electron transfer and photoisomerization, are
in general inseparable and need to be treated in a unified manner. We finish by
discussing how the efficiency of photoisomerization-coupled electron transfer
can be controlled experimentally.
