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.