  In a pair of coupled donor-acceptor conjugated polymer chains, it is possible
for an exciton photoexcited on either polymer to decay into a hole in the donor
polymer's valence band and an electron in the conduction band of the acceptor
polymer. We calculate the corresponding exciton decay rate and its dependence
on inter-polymer distance. For a pair of derivatives of poly(phenylene
vinylene), PPV, specifically poly[2-methoxy, 5-(2$^\prime$-ethyl-hexyloxy)-1, 4
PPV], MEH-PPV, and poly(2,5-hexyloxy $p$-phenylene cyanovinylene), CN-PPV, at a
separation of 6 \AA the characteristic decay time is 2.2 ps, whereas at 4 \AA
it is $\sim 50$ fs.
