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.