Photo-induced hydrous organic aggregates for photoactivatable luminescence

Harnessing light to regulate molecular aggregation behavior has become an essential approach to confer useful properties for functional materials at the aggregate level. Current examples of photo-induced aggregation predominantly occur in solution, but the solvent—ubiquitous as it is—is often overlooked as a potential participant in the aggregation process. In this study, photo-induced hydrous organic aggregates (HOA) are reported based on a hydrophobic nitroaromatic compound (NPAC). NPAC is non-emissive in both the molecule and anhydrous organic aggregate (AOA) states. In the presence of water and upon photo-irradiation, excited state NPAC co-assemblies with water via strong electron donor-acceptor interactions to form HOA, exhibiting intense luminescence (quantum yield = 58.88%) with characteristic dual-emission features. Experimental and theoretical data reveal that the bond angle in the nitro group is the key factor for modulating the excited behaviors of NPAC, with dual emissions originating from the locally excited (LE) state and the charge transfer (CT) state during the excited-state protonation process. Additionally, the high-contrast photoactivation process can be successfully applied in bioimaging and photodynamic therapy. This work offers valuable insights into modulating molecular aggregation based on the excited states of molecules, facilitating the advancement of photoactivatable luminescent materials.