We have investigated the optical properties of a pi-conjugated poly(arylene-ethynylene) co-polymer, the poly-{[(2,5-dioctyloxy)-1,4-phenylene acetylene]-co-2,6-pyridylene acetylene}, in liquid solutions and blended films with nonconjugated polymers. The red-shifted emission from excimers strongly influences the photoluminescence of solid-state samples but it can be suppressed by using in-vacuum thermal ageing or photoirradiation. Experimental observations suggest this quenching is due to structural reorganization processes that still occur in blends within phase-separated regions of pure co-polymer. Significantly, the suppression of the excimer band does not affect the exciton blue emission in blends, which could help improve color purity for OLEDs and display applications. (c) 2005 Elsevier B.V. All rights reserved.