Insights into the Photodynamics of the Fluorescence Emission and Singlet Oxygen Generation of Fluorogen Activating Protein-Malachite Green System.

The self-assembled fluorogen activating protein (FAP)- malachite green (MG) complex is a well-established protein-ligand system, which can realize binding-caused fluorescence turn-on of MG and singlet oxygen ( 1 O 2 ) generation by MG iodination. To clarify the mechanism of fluorescence activation and the 1 O 2 generation, the photodynamics of different halogen-substituted MG derivatives and their corresponding MG-FAP complexes were studied by femtosecond transient absorption spectroscopy and theoretical computation. The results show that the rotation of MG was restricted by FAP binding, which preventing the rapid internal conversion and allowing a long lifetime for the excited MG to undergo fluorescence emission and intersystem crossing. Moreover, these MG-FAP complexes exhibit obviously varied fluorescence quantum yields ( Φ FL ) and 1 O 2 yields. The study on the decay pathways indicates that such an anti-heavy atom effect predominately stems from the lifetimes of the excited-state species. The photodynamic mechanism study here will lead to more advanced FAP-MG systems with high spatiotemporal resolution.