Substituent Effect On Properties Of Fluorescence PH Probes Based On Hemicyanine

Chapter 1:In the chapter,the kinds,the effects on molecular properties and research methods of substituents were discussed.And the research progress of hemicyanine pH fluorescent probes with different substituent was reviewed.We presented our research content on the basis of the summary of previous work.Chapter 2:Spiropyran compounds,which are well known as an interest isomerization of systems,the closed spiropyran?SP?could be converted into the open merocyanine?MC?in the presence of an acid and form more stable protonated merocyanine?MCH?.In order to understand how the substituent affect the isomerization of spiropyran.A series of the chromene 7-subsituted spiropyran compounds were designed and synthesized.The photophysical properties of them were studied comparatively by UV-absoption and fluorescence spectra in different pH.The results demonstrated that the various substituents affected not only the photophysical properties of SP,MC and MCH forms,but also the pK_a of the MC-MCH transformation.There was good linearity relationship between the pK_a and the Hammett constant of substituent,the pK_a was smaller when the Hammett constant of substituent was larger.Chapter 3:Fluorescent probes?1 and 2?for pH based on semi-cyanine were synthesized from indole?benzo indole?derivatives and 4-hydroxybenzaldehyde using one-step condensation reaction.The probes have good water solubility and stable luminescence properties.They can be used to detect pH of acidic and alkaline solutions by the UV absorption spectra or ratiometric fluorescence spectra.The pK_adates of probe 1 are the 3.81 and 10.01,and the pK_adates of probe 2 are 4.03and 10.47.Both pH probes have some advantages,such as large Stokes shift,high sensitivity and good reversibility.Compared to the two probes,the 1 is more sensitive to the alkalinity,and the 2 is more sensitive to the acidity.Chapter 4:A series of fluorescent probes with different substituents?NH₂,OH,H,Br,NO₂?for pH based on semi-cyanine were synthesized from indole 4-Picoline and 4-R benzaldehyde using one-step condensation reaction.The absorbance and fluorescence spectra of these compounds in different pH environments were determined,and the experimental results showed that both absorbance and fluorescence spectra could detect the pH change in solution,and the detection range is wide.The pH detection range and pK_a value of the compound changed with the substituent push-pull electron ability.With the enhancement of the substituent pushing electronic capabilities,the maximum absorption and the emission peak of the probe red shift,at the same time the pK_a value becomes smaller.