The influence of side chains, film thickness, and thermal treatment of .pi.-conjugated polymers on emission colors, was studied. The resp. thickness libraries of six alkoxy-substituted poly(p-phenylene ethynylene)-alt-poly(p-phenylene vinylene)s (PPE-PPVs) were prepd. by inkjet printing. The optical properties of the printed libraries were screened utilizing high-throughput methods. The emission colors of the studied polymers strongly depend on the inter-chain interactions which are increased with increasing film thickness and influenced by the side chains. Upon annealing at 70, white emission was obsd. from the printed films.