Viscosity Fluorescent Probes Based on Quinoline Group and Its Applications

As one of the important parameters of biological microenvironment, viscosity is closely related to many life activities, when diseases appear in the organism, such as pneumonia, diabetes, Alzheimer's disease, atherosclerosis, malignant tumors, etc., the cytoplasmic viscosity in the organelle also changes, the new crown pneumonia is becoming more and more serious, and it is urgent to detect the viscosity in the organism. Based on the fluorescence mechanism of twisted intramolecular charge transfer (TICT), a viscosity-mediated fluorescent probe QUI-VI is rationally designed and constructed, and its related properties are explored and applied to detect physiological viscosity changes in vivo to achieve the purpose of disease monitoring. The two conjugates were connected by the carbon-carbon double bond formed by the condensation of aminotrinitrobenzene and benzopyridine quaternary ammonium salts by methyl and aldehyde groups, forming a large conjugated system. This not only increases the free transfer of electrons in the conjugated system, so that the constructed probe molecules have a long emission wavelength, but also regulates the fluorescence signal of the probe molecules because the freely rotatable carbon-carbon double bond can respond to the change of viscosity. The regulation process is: when QUI-VI is in a high-viscosity environment, the free rotation of the carbon-carbon double bond is greatly limited, so that the two conjugated systems on the molecule are in the same plane, at this time, the probe molecule is the lowest energy state, when irradiated by 450 nm light, absorb one photon energy. The molecule is excited in the excited state, and can emit long-wavelength fluorescence when transitioning back to the ground state. On the contrary, when it is in a medium with low viscosity, the free rotation of the carbon-carbon double bond is no longer hindered, and when the two conjugated systems rotate to the same plane perpendicularly, they are in the highest energy state, and the molecules emit shorter wavelengths of fluorescence when absorbing the energy of a photon and transitioning back to the ground state, that is, it is blue-shifted by 10 nm on the fluorescence spectrum. All in all, the fluorescence change of the probe QUI-VI constructed based on the TICT mechanism is controllable.