fused-dihydropyridazine N-aryl aza[5]helicene derivatives” (PDH) with a helical structure inspires the demonstration of intrinsic photo-triggered multi-functional properties based on a Kekulé biradical and structural flexibility. Multiple functions, such as T-type photochromism, photo-excitation-mediated triplet biradical formation, and photoracemization, which are attributed to PDH, are revealed.