  Conjugated polymers are observed to aggregate in solution. To account for
this observation we propose a inter-chain binding mechanism based on the
intermolecular tunneling of the delocalized $\pi$-electrons occurring at points
where the polymers cross. This tunneling mechanism predicts specific bound
structures of chain that depend on whether they are semiconducting or metallic.
Semiconducting chains should form polyacene-like states exhibiting binding at
every other site, while (doped) metallic chains can bind at each site. We also
show that solitons co-localize with the intermolecular binding sites thereby
strengthening the binding effect and investigate the conformational statistics
of the resulting bimolecular aggregates.
