Positional Isomerism Regulates ESIPT & TICT Balance in Rosin‐Based BioAIE Luminogens †

Comprehensive Summary Organic luminescent materials are highly structure‐sensitive, where subtle changes in skeleton or substituents can significantly modulate excited‐state routes toward luminescence, a feature of particular interest in rapidly developing bio‐based systems. In this work, a series of rosin‐based electron donor‐acceptor type biomass‐based aggregation‐induced emission luminogens is designed and synthesized to explore the effect of positional isomerism on luminescence. The rosin skeleton undergoes condensation with the salicylaldehyde motif, acting as a distinctive natural electron acceptor moiety. Both photophysical and theoretical results confirm that positional isomerism modulates the steric conformation and electronic coupling, thereby dynamically regulating the competitive interplay between excited‐state intramolecular proton transfer and twisted intramolecular charge transfer. Notably, the meta ‐substituted isomer DAMB‐SA‐ m ‐TPA, benefiting from moderate torsional freedom, undergoes a mild conformational evolution that gives rise to the most pronounced twisted intramolecular charge transfer‐induced red‐shift with the variation of polar solvents. Furthermore, these compounds demonstrate potential for multi‐stimuli responsive information security applications. This work not only demonstrates the effectiveness of using positional isomerism to regulate optical properties but also provides a strategy for converting renewable rosin into high‐value functional optical materials.