Controllable photo-physical and aggregating properties of D-π-A perylene diimide derivatives by introducing soft/hard substituent on the bay position

Comparative discussions on photo-physical and aggregating properties of D-π-A perylene diimide derivatives with soft n-octylamine (PDI-soft) and hard quinoidal (PDI-hard) substituents on the bay position were put forward to reveal structure-property relations. UV-vis spectrometer and fluorospectro photometer were used to characterize the absorption and emission properties of derivatives in various solutions. The PDI-hard aggregated in both Hexane and THF/water systems and showed an interesting time-dependent aggregation-induced enhanced emission (AIEE) phenomenon. PDI-soft also aggregated in poor solvents as Hexane or Acetonitrile and exhibited broad light absorption range making PDI-soft a candidate for photoelectric materials. Morphologies of solid aggregations formed from solutions were observed by means of scanning electron microscopy. Results showed that PDI-hard molecules aggregated to sheets structure after the evaporation of Hexane while PDI-soft obtained a wire-like structure through a slipped π-π stacking in the system of THF and water. The comparison of photo-physical properties and morphologies between PDI-hard and PDI-soft suggests that a subtle choice of the bay substituents makes the controllable photo-physical and aggregating properties possible.