Diazocine Derivatives: A Family of Azobenzenes for Photochromism with Highly Enhanced Turn-On Fluorescence.

π-Conjugated azobenzene derivatives were reported to couple azo moieties with aryl fluorophore. Using the photochemistry of the C-bridged azobenzene, we have accomplished two diazocine-based photoswitching molecules (cAz1 and cAz2). In addition to remarkable photochromic properties, they show a turn-on fluorescence, and the emission was highly enhanced with quantum efficiency increasing up to 0.22 for cAz1. The emission remains persistent and can only be switched off via thermal deactivation. They display greater optical responses, compared with the linear analogues (Az1-Az4). This work may provide a new scaffold toward advanced light-emitting materials using photoswitchable systems.