Modulation of Donor in Purely Organic Triplet Harvesting AIE‐TADF Photosensitizer for Image‐guided Photodynamic Therapy

Abstract Image‐guided photodynamic therapy is acknowledged as one of the most demonstrative therapeutic modalities for cancer treatment because of its high precision, non‐invasiveness, and improved imaging ability. A series of purely organic photosensitizers denoted as BTMCz, BTMPTZ, and BTMPXZ , have been designed and synthesized and are found to exhibit both thermally activated delayed fluorescence and aggregation‐induced emission simultaneously. Experimental and theoretical studies are combined to reveal that modulation of the donor of the photosensitizer enables distinct thermally activated delayed fluorescence via a second‐order spin‐orbit perturbation mechanism involving lowest singlet charge‐transfer and higher‐lying triplet locally excited states, respectively. Further, different donor strengths and unique aggregations (H‐, J‐ and X‐type packings) greatly influence their color‐tunable up‐converted luminescence and endow them with superb dispersibility in water. The confocal microscopy‐based cellular uptake study confirms the successful internalization of the nano‐probes, while BTMCz enables the generation of reactive oxygen species (singlet oxygen) under white‐light irradiation, enabling the efficient killing of cancer cells.