Self-assembly, protonation-dependent morphology, and photophysical properties of perylene bisimide with tertiary amine groups

It is crucial to tune the morphology of aggregates to obtain functional photoelectric properties in perylene bisimide (PBI). The associated properties can be controlled by appropriate molecular design and by tuning the self-assembly conditions. However, many studies only focused on the modification with easily-protonated groups at the bay positions of perylene bisimide, which greatly limited their potential applications. In this work, four PBI derivates bearing tertiary amine groups at the imide positions were synthesized and their self-assembly with different concentrations of hydrochloric acid were performed. The final morphology and the properties of the aggregates were tuned by modifying the charge interaction in addition to π-π stacking and hydrophobic interactions. The evolution of the specific morphology with the acidity of the self-assembly conditions was discussed and the molecular structure was optimized. The photophysical properties of the aggregates were characterized by UV–visible and fluorescence spectroscopy . The shapes of the spectra varied with the molecular structures and the acid concentration. Moreover, the emission spectra of the aggregates experienced a large Stokes shift. The color of the aggregates formed from the three derivates (MDI-PBI, EDI-PBI, and AEP-PBI) changed from red to blue upon protonation. These derivatives may have potential applications in organic photoelectric functional devices where a strict morphology or size is needed. The protonation-dependent morphology, the color change, and the large Stokes shift makes the aggregates potential candidate for fluorescent probes or pH sensors.