Deep Red Emissive Aliphatic Oligomeric Polyphosphate Esters from the n –π Interaction Enhanced Spatial Electronic Delocalization

Unconventional fluorescent polymers have garnered increasing attention due to their unique optical properties and broad applications in bioimaging, chemical sensing, and security encryption. In this study, a series of aliphatic oligomeric polyphosphate esters were synthesized to explore the relationship between fluorescence behavior and molecular structure. These newly prepared polymers exhibit notable optical characteristics, including deep-red emission, excitation-dependent fluorescence, concentration-enhanced luminescence, and aggregation-induced red-shifted emission. Experimental data combined with theoretical calculations revealed that intermolecular and intramolecular interactions promote molecular aggregation and functional group clustering, leading to enhanced n –π interactions. These strengthened n –π interactions subsequently facilitate spatial electronic communication, resulting in a prominent red fluorescence. Studies showed that polymerization and aggregation induce concentrated negative Mulliken charges and centered electrostatic potential, resulting in enhanced electronic communication and emission. Moreover, these polymers were used in the preparation of fluorescent hydrogels. This work gains new insight into the study of the emission mechanism of unconventional fluorescent polymers.