Tuning Charge-Transfer and Excited-State Relaxation Pathways in Anthracene-Based Donor–Acceptor AIEgens through Substituent and Environmental Control

Precise control of charge-transfer (CT) and excited-state relaxation pathways is crucial for designing efficient donor–acceptor (D–A) fluorophores. Here, we investigate a series of novel anthracene-based imine-linked D–A chromophores bearing electron-donating and electron-withdrawing substituents at different positions to establish how substituent identity and the local environment impact the excited-state behavior. Spectroscopic studies reveal that solvent polarity shifts the population balance between locally excited (LE) and charge-transfer (CT) states, leading to a redistribution of excited-state populations rather than an alteration of the intrinsic decay kinetics. Nitro substitution induces ground-state polarity reflected by negative solvatochromism in the absorption spectrum, while emission in all derivatives arises from the stabilized CT state, exhibiting a systematic red shift with solvent polarity. Aggregation and metal ion coordination both suppress excited-state torsional relaxation, leading to enhanced emission and simplified decay dynamics, demonstrating that aggregation-induced emission and sensing responses originate from a common restriction of nonradiative pathways. Computational analysis supports the substituent-dependent orbital localization governing CT characteristics. A key finding of this study is that we turn the conventionally known fluorescence-quenching −NO 2 electron-withdrawing group into a functional advantage, enabling highly sensitive detection of biologically and environmentally relevant metal ions alongside pronounced aggregation-induced emission.