Manipulating Host‐Guest Charge Transfer of a Water‐Soluble Double‐Cavity Cyclophane for NIR‐II Photothermal Therapy

Abstract

Water‐soluble small organic photothermal agents (PTAs) over NIR‐II biowindow (1000–1350 nm) are highly desirable, but the rarity greatly limits their applications. Based on a water‐soluble double‐cavity cyclophane GBox‐44+, we report a class of host–guest charge transfer (CT) complexes as structurally uniform PTAs for NIR‐II photothermal therapy. As a result of its high electron‐deficiency, GBox‐44+ can bind different electron‐rich planar guests with a 1 : 2 host/guest stoichiometry to readily tune the CT absorption band that extends to the NIR‐II region. When using a diaminofluorene guest substituted with an oligoethylene glycol chain, the host–guest system realized both good biocompatibility and enhanced photothermal conversion at 1064 nm, and was then exploited as a high‐efficiency NIR‐II PTA for cancer cell and bacterial ablation. This work broadens the potential applications of host–guest cyclophane systems and provides a new access to bio‐friendly NIR‐II photoabsorbers with well‐defined structures.

Preparation and characterization of NIR photothermal agents with high biocompatibility

“…7a). With the enhancement of the electrondonating ability from Guest 1 to Guest 3, the intensity of the absorption peak of PDI decreases and gradually redshifts, indicating that there are donor-acceptor π-π interactions between the guest molecules and GBox-1ꞏ4Cl [9]. In addition to the change of the UV-visible absorption peak, the fluorescence properties of GBox-1ꞏ4Cl solution also changed significantly after the addition of guest molecules, we further compared the binding force between Guest 1-3 and GBox-1ꞏ4Cl by fluorescence titration (Fig.…”