Novel Tetraphenylporphyrin‐Modified Pyrazolylazobenzene Derivative as Photoswitch: Design, Synthesis, and Photoswitching Behavior Research Combined With Controllable Fluorescence Properties

ABSTRACT A novel photochromic azoporphyrin compound was designed and synthesized, featuring a covalent linkage through an amide bond. The compound, designated as 5,10,15‐triphenyl‐20‐{4‐[4‐(2‐(3,5‐dimethyl‐1 H ‐pyrazol‐4‐yl))diazenyl]benzamido}phenylporphyrin ( TPP‐AAP ), incorporates an azo‐functional group that confers photochromic properties. Its molecular structure and photochromic properties were characterized using NMR spectroscopy, UV–vis spectroscopy, and fluorescence spectroscopy. Upon the addition of a weak base (Na 2 CO 3 ), the azo unit of TPP‐AAP underwent trans→cis isomerization upon irradiation at 254 nm UV light; the reverse process ( cis→trans ) could be induced by subsequent irradiation with 450 nm visible light. The compound maintained stable antifatigue performance after multiple cycles. Fluorescence spectral analysis revealed that upon UV irradiation, the intense Q(0,0) emission band at 652 nm was significantly quenched. Concurrently, the Q(0,1) band at 718 nm underwent a blue shift to 706 nm, accompanied by an increase in intensity. These results demonstrate that the molecular conformational change significantly modulates the excited‐state relaxation pathway. Consequently, the corresponding fluorescence signal provides an effective mechanism for nondestructive readout.