Self-Assembled Metal-Organic Framework Stabilized Organic Cocrystals for Biological Phototherapy.

Organic self-assembled co-crystals have garnered considerable attention due to their facile synthesis and intriguing properties, such as room temperature ferroelectricity and two-photon absorption ability. However, the supramolecular interactions of co-crystals restrict their stability in the aqueous solution phase, which is especially important for biological applications. Herein, we reported on the proof-of-concept biological application of self-assembled organic co-crystals via the construction of metal-organic framework (MOF) -stabilized co-crystals. In particular, we built an electron-deficient MOF with naphthalene diimide (NDI) as the ligand and biocompatible Ca 2+ as the metal nodes. An electron donor molecule, pyrene, was encapsulated to form the host-guest MOF self-assembled co-crystal. We observed that such MOF structure leads to uniquely high-density ordered arrangement and the close intermolecular distance (3.47 A) of the charge transfer pairs. Hence, the concomitant superior charge transfer interaction between pyrene/NDI can be enhanced and the resultant photothermal conversion efficiency of Py@Ca-NDI in aqueous solution can thus reach up to 41.8%, which, to the best of our knowledge, is the highest value among the reported organic co-crystal materials as well as most of the reported MOFs. Based on this realization, as a proof of concept, we demonstrated that such a self-assembled organic co-crystal platform can be used in biological applications that are exemplified via highly effective long wavelength light photothermal therapy. This conceptual work demonstrates the feasibility of using organic co-crystals in aqueous solution and should pave the way to a wide variety of photonic and biophotonic applications via such new platforms.