Amine‐Triggered Azabenz‐Annulation of Cyclic Secondary Amine‐Functionalized Perylene Diimides for Dual‐Mode Sensing

Volatile amines are key indicators of food spoilage and industrial safety, yet many existing molecular probes are often limited by poor visual contrast, a lack of intuitive signalling, and restricted to solution-phase detection. Cyclic secondary amine perylene diimide (CyNHPDI) intermediates, accessible through the Pictet-Spengler reaction, are an attractive system because their conversion to azabenz-annulated PDIs (AzaBPDIs) can, in principle, deliver distinct green-to-yellow color changes and bright fluorescence turn-on. However, aldehyde-derived CyNHPDIs are reactive but air-sensitive, limiting controlled conversion, while ketone-derived analogues are stable but unreactive. Here, we resolve these issues by introducing N1, a ninhydrin-derived CyNHPDI that is both air-stable and chemically reactive, enabling triggered conversion to AzaBPDI upon exposure to volatile amines in both solution and films. N1 undergoes a green-to-yellow color change with a ∼330-fold fluorescence turn-on and a sterically and substituent controlled reactivity trend (primary >> secondary > tertiary amines). Large-area N1 films roll-coated from a nonhalogenated solvent extend these dual responses into a practical, visually intuitive green (safe) to yellow (warning) palette with high contrast. Mechanistic studies clarify the amine-triggered pathway from N1 to AzaBPDI, providing a connection between the molecular transformation and the observed visual outputs. This work establishes a design principle for volatile amine sensing and demonstrates a platform in both solution and large-area films, combining mechanistic insight with practical applicability.