Interplay of Molecular Twisting and π‐Spacer Conjugation of Donor‐π‐Acceptor Molecules in Governing Charge Transfer and Stimuli‐Responsive Luminescence

We report the design, synthesis, and photophysical characterization of a series of twisted donor‐π‐acceptor (D‐π‐A) molecules that exhibit diverse stimuli‐responsive luminescence behaviors. By systematically varying the π‐spacer, we elucidate how molecular twisting modulates intramolecular charge transfer (CT), aggregation‐induced emission enhancement (AIEE), and external stimuli responses. Structural analyses and density functional theory calculations reveal that increasing dihedral distortion between donor and acceptor units disrupts π‐conjugation, leading to reduced CT stabilization and altered excited‐state relaxation pathways. All compounds display pronounced positive solvatochromism, consistent with CT‐dominated excited states. Lippert–Mataga analysis establishes a direct correlation between excited‐state dipole moments and molecular twisting, with less‐twisted frameworks exhibiting stronger CT stabilization. The molecules also show distinct AIEE behavior and reversible acid/base‐responsive fluorescence switching, while the highly twisted P3A demonstrates reversible mechanochromic luminescence accompanied by crystal‐to‐amorphous phase transitions. Collectively, these results underscore the critical role of π‐spacer conjugation and molecular geometry in directing photophysical processes and provide mechanistic insights for designing next‐generation, stimuli‐responsive luminescent materials for sensing applications.