Simultaneous Increase in Brightness and Singlet Oxygen Generation of an Organic Photosensitizer by Nanocrystallization

Abstract Efficient organic photosensitizers are attractive for cancer cell ablation in photodynamic therapy. Bright fluorescent photosensitizers are highly desirable for simultaneous imaging and therapy. However, due to fundamental competition between emission and singlet oxygen generation, design attempts to increase singlet oxygen generation almost always leads to the loss of fluorescence. Herein, it is shown for the first time that nanocrystallization enables a simultaneous and significant increase in the brightness and singlet oxygen generation of an organic photosensitizer. Spectroscopic studies show simultaneous enhancement in the visible light absorption and fluorescence after nanocrystallization. The enhanced absorption of visible light in nanocrystals is found to translate directly to the enhanced singlet oxygen production, which shows a higher ability to kill HeLa cells as compared to their amorphous counterpart.