Controlled Generation of Singlet Oxygen in Living Cells with Tunable Ratios of the Photochromic Switch in Metal-Organic Frameworks.

Development of a photosensitizing system that can reversibly control the generation of singlet oxygen ((1) O2 ) is of great interest for photodynamic therapy (PDT). Recently several photosensitizer-photochromic-switch dyads were reported as a potential means of the (1) O2 control in PDT. However, the delivery of such a homogeneous molecular dyad as designed (e.g., optimal molar ratio) is extremely challenging in living systems. Herein we show a Zr-MOF nanoplatform, demonstrating energy transfer-based (1) O2 controlled PDT. Our strategy allows for tuning the ratios between photosensitizer and the switch molecule, enabling maximum control of (1) O2 generation. Meanwhile, the MOF provides proximal placement of the functional entities for efficient intermolecular energy transfer. As a result, the MOF nanoparticle formulation showed enhanced PDT efficacy with superior (1) O2 control compared to that of homogeneous molecular analogues.