Viscosity-responsive Fluorescent Probes And Effect Of Molecular Structure On Their Photophysical Properties And Cell Targeting Ability

There are many physical and chemical factors affect the nonnal physiological activities of cells,for example:acidity(pH),viscosity,temperature,polarity,and concentration.Viscosity is an important factor in intracellular microenvironment,it plays an important role in maintaining cells normal life activities.Cells contain plasma membranes and cytoplasm,both of which are viscous.The change of plasma membrane viscosity is closely related to many physiological processes of cells,which can directly affect the activity of membrane binding proteins.The abnormal viscosity of plasma membrane even lead to a variety of diseases.For example,the excessive viscosity of red blood cell could cause liver function abnormality,the excessive viscosity of white cell membrane could cause accelerated aging,and the abnormal cytoplasmic viscosity will affect cardiopulmonary function.Abnormal lysosomal viscosity is associated with inflammation and even cancer.The abnormal viscosity of lipid droplets means that the distribution of lipid in cells is abnormal,which means that lipid is related to many diseases(obesity,fatty liver).The abnormal viscosity of mitochondrial(the abnormal viscosity of mitochondrial membrane)is related to Parkinson's disease and diabetes.Therefore,it is of great significance to monitor the viscosity changes of mitochondria?plasma membrane and other organelles for physiology and pathology.Owing to fluorescent probes with the advances of real-time,in situ and high signal-to-noise ratio imaging,they are obviously a very good carrier and tool for monitoring the microenvironment in cells.Molecular rotor probes are very sensitive to viscosity.When the intramolecular rotation of some probes with D-?-A structures is restricted,the fluorescence intensity increases dramatically.The rotor-type fluorescent probes can be designed to study intracellular viscosity changes using this property of the molecular rotor.We can design the probes by the charactertistic of molecular rotor-type.Then we can study the viscosity change of intracelluar.The practical significance of this paper is to develop a series of viscosity responsive fluorescent probes and to detect the effects of rigid structure,length of side alkyl chains and substituents on photophysical properties and cellular targeting.We selected 9-phenyl-carbazole and triphenylamine as precursors,and coupling with pyridine salt through Knoevenagel mechanism so as to increase the degree of conjugation.Based on the states above,we designed and synthesized two serious of probes named TAPI-n and PCPI-n.Then explored the optical properties of four probe molecules(TAPI-1,TAPI-6 and PCPI-1,PCPI-6).Through fluorescence spectrum experiment in different polar solvents,it can be found that TAPI-1 is sensitive to viscosity,and their fluorescence intensity are different in various solvents.The fluorescence intensity varies greatly.PCPI-1 also responded to viscosity and there is little change in fluorescence intensity.It is worth noting that the fluorescence quantum yield of PCPI-1 is much higher than that of TAPI-1.By testing the ultraviolet absorption spectrum and fluorescence emission spectrum of the probes in different polar solvents,it was found that through change the length of the side alkyl chain did not change the optical properties of the probes,such as the maximum absorption peak,maximum fluorescence emission peak and fluorescence quantum yield.Cell staining and fluorescence imaging revealed that TAPI-1,TAPI-6 and PCPI-1,PCPI-6 all preferentially target mitochondria due to electrostatic interactions with the negative mitochondrial membrane potential.TAPI-12,TAPI-16 and TAPI-18 fluorescence probes respectively imaging the mitochondria,lipid droplets and cell membranes,while PCPI-12,PCPI-16 and PCPI-18 fluoresence probes respectively imaging the mitochondria,cell membranes and cell membranes.HOPI-18,MOPI-18 and AOPI-18 were designed and synthesized by modification of hydroxyl functional groups.After cell staining and fluorescence imaging,it was found that HOPI-18 had serious internalization in addition to the target cell membrane.And probes MOPI-18 and AOPI-18 both target cell membranesFinally,red fluorescence probes has the advances of tissue penetration and lower light damage,and is more suitable for imaging in tissues.The TAPI-n series of red fluorescence probes designed by us has the potential to image tissueIn conclusion,we designed and developed three types of pyridine cationic salt fluorescent probes with D-?-A structure,and investigated the effects of rigid structure,side chain alkyl chain length,substituents and other factors on photophysical properties and cellular targeting.