Push–Pull Bridged Stilbenes as Small Solvatochromic Aggregation‐Induced Emission Luminogen: Design and Excited‐state Deactivation Dynamics

ABSTRACT Aggregation‐induced emission luminogens (AIEgens) are typically large π‐conjugated molecules, but their low affinity and noninvasiveness toward analytes limit practical applications. To address this, smaller, more planar AIEgens are needed. Stilbene, though structurally suitable, lacks visible luminescence. Here, we report a minimally modified stilbene‐based AIEgen—4‐dipropylamino‐4’‐cyano‐bridged stilbene ( DpCBS[7] )—that exhibits fluorescence solvatochromism and efficient AIE across a broad polarity range in the visible region. DpCBS[7] exhibits low quantum yields ( Φ fl = 0.01–0.04) in solvents from nonpolar n ‐hexane to polar dimethyl sulfoxide, with large Stokes shifts, viscosity‐sensitive luminescence, and highly efficient solid‐state luminescence ( Φ fl = 0.70). To elucidate its dual solvatochromic and AIE behavior, femtosecond transient absorption spectroscopy was conducted. In solution, DpCBS[7] displays transient absorption with lifetimes of 21 ps (toluene) and 56 ps (acetonitrile) at 293 K, indicating ultrafast nonradiative decay leading to low Φ fl . Arrhenius analysis over the temperature range of 263–313 K revealed activation energies (Δ E a ) of 9.90 kJ/mol in toluene and 12.8 kJ/mol in acetonitrile for the S 1 → S 0 decay of DpCBS[7] . The Δ E a values show no clear systematic dependence on solvent polarity. In contrast, pre‐exponential factor A remains consistently high regardless of solvent polarity, indicating that the striking photophysical response is governed primarily by the pre‐exponential factor rather than by modulation of the activation energy. These findings highlight the fundamental importance of tailoring the distribution function through structural modification as a robust strategy to control AIE characteristics.