Tuning the Formation of J and H Aggregates in Diketopyrrolopyrrole Materials

The aggregation of molecules in devices plays a central role in determining their functional properties. In the aggregated state, pi conjugated chromophores can exhibit enhanced emission in comparison to their dilute solution. Here we synthesize and characterize a diketopyrrolopyrrole (DPP) based donor-acceptor molecule in terms of its optical properties in solution and thin film. Temperature and concentration dependent photoluminescence studies reveal the presence of both H and J aggregates in thin film, which is corroborated by computational investigations of the coulombic coupling in the crystal structure of the DPP derivative. We find that the type of aggregate formed is extremely sensitive to the variation in the shearing angle between the monomers in the crystal structure geometry.