Strategies to reduce inter-chain aggregation and fluorescence quenching in alternated multilayers of a polythiophene

Electrostatically self-assembled multilayers of a fluorescent carboxyalkylsulfanyl polythiophene and poly(diallyldimethylammonium) were prepared using the layer-by-layer deposition approach and were structurally characterized by linear dichroism and atomic-force microscopy. Steady-state measurements revealed that fluorescence was quenched relative to the solution behaviour. The emission quantum yield was found to increase upon decreasing the polymer concentration in the dipping solution as well as by co-depositing polythiophene with another polyanion, poly(sodium-4-styrenesulfonate). Fluorescence quenching was therefore attributed to the formation of non-emitting inter-chain aggregate exciton traps. Intercalation of polythiophene layers with non-emitting polymers having larger energy gaps did not result in enhanced fluorescence, thus suggesting negligible polythiophene aggregation and exciton migration across different layers. At best, we could obtain quantum yields around 0.1–0.15, about half the solution value but almost two orders of magnitude larger than found with cast or spin-cast films.