Engineered Design of a Photothermal NIR‐II Fluorescent Probe for Efficient Tumor Theranostics

Abstract Near‐infrared (NIR) fluorescent emitters are promising for biomedical use as photothermal transducers, but balancing photothermal conversion efficiency (PCE) and fluorescence imaging is challenging. A “fused ring” molecular design is employed to enhance photothermal agents, transforming the linear “Donor‐Acceptor‐Donor” structure into planar star‐shaped molecules. 4,4′,4″,4‴‐(dibenzo[a,c][1,2,5]thiadiazolo[3,4‐i]phenazine‐2,7,10,14‐tetrayl)tetrakis(N,N‐diphenylaniline) (DTP‐27) and 4,4′,4″,4‴‐(dibenzo[a,c][1,2,5]thiadiazolo[3,4‐i]phenazine‐3,6,10,14‐tetrayl)tetrakis(N,N‐diphenylaniline) (DTP‐36) is synthesized. Simulations indicates the primary electron cloud distribution at the 10,14‐position triphenylamine and receptor. Adding 2,7‐ and 3,6‐position triphenylamines further reduces the bandgap and enhances photothermal conversion. The nanoparticles shows high NIR‐II fluorescence quantum yields, excellent PCE, and biocompatibility, effectively eradicating tumors in 4T1‐bearing mice under fluorescence imaging guidance.