Construction of Through‐Space Charge‐Transfer Nanoparticles for Facilely Realizing High‐Performance NIR‐II Cancer Phototheranostics

Phototheranostics with second near‐infrared (NIR‐II) emissions show great potential for disease diagnosis and imaging‐guided phototherapy owing to deep tissue penetration, high imaging resolution, and excellent tumor eradication. Recently, molecular conjugation engineering and J‐aggregation have been used to construct organic NIR‐II materials. However, these molecules generally have extensive conjugation and large molecular weight in the range of 700–1700 g mol−1, requiring complicated molecular design and synthesis. Herein, a NIR‐II emissive through‐space charge‐transfer (TSCT) nanoparticle (NP) using short‐conjugated donor‐acceptor (D‐A) molecules (TTP) is reported for high‐performance bioimaging and cancer phototheranostics. Owing to the short conjugation of the TTP molecule with a small molecular weight of only 518 g mol−1, the TTP monomer possesses visible absorption and first near‐infrared (NIR‐I) emission. Upon forming NPs in water, the efficient TSCT between TTP monomers leads to significantly red‐shifted absorption to the NIR‐I and emission to the NIR‐II region with a tail that extends to 1400 nm. TTP NPs are employed in NIR‐II in vivo blood‐vessel bioimaging and cancer phototheranostics successfully. This work introduces a facile strategy to construct NIR‐II emissive NPs based on short‐conjugated D‐A molecules for high‐performance biomedical applications. NIR‐II emissive through‐space charge‐transfer (TSCT) nanoparticles (NPs) of small‐size TTP molecules are reported. Owing to the short conjugation of the TTP molecule with a small molecular weight of only 518 g mol‐1, it shows visible absorption and NIR‐I emission. After forming nanoaggregates, the efficient TSCT between monomers contributes to significantly red‐shifted optical properties in NP which are applied in NIR‐II bioimaging and cancer phototheranostics.