We designed two cruciform-structured oligo(phenylenethynylene) (OPE) molecular wires for probing the intra- and inter-molecular exciton migration pathways, and constructed highly ordered molecular assembly using Langmuir-Blodgett (LB) technique. Minor structural variation turns out to influence significantly exciton migration routes. Though the molecular structures are similar, these two molecules exhibit distinct exciton migration behaviors. Intermolecular exciton migration is observed in unmodified molecular wire OPE1; while only intramolecular exciton migration is allowed in the side-chain modified molecular wire OPE2. This work presents a facile strategy for controlling exciton migration in solid state, and provides useful insights for designing active components for opto-electronic devices. (C) 2011 Elsevier B.V. All rights reserved.