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

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.