We have investigated the influence of molecular arrangement on the transfer rates of photoexcitations along supramolecular assemblies of hydrogen-bonded oligo-p-phenylenevinylene (OPV) molecules for two different packing geometries. For well-defined, helical stacks of monofunctional OPVs fast (approximate to 50 ps) photoluminescence depolarization and excitation transfer to dopants was observed, in agreement with semi-coherent exciton diffusion. For disordered assemblies of bifunctional OPVs incorporating a spacer to link adjacent molecules, depolarization and energy transfer dynamics occur on a longer time scale (, nanosecond). This strongly suggests that such spacers need to be tuned carefully as they may otherwise interfere with the pi-stacking thereby reducing the intermolecular electronic coupling. (c) 2005 Elsevier B.V. All rights reserved.