Conjugated Pi-Systems With PET Characteristics For Reaction-based Fluorescent Probes

There are a variety of species which play critical physiological roles in the living body,such as small molecules,free radicals,ions,peptides,enzymes,etc.Therefore,it is crucial to develop efficient detection protocols in clinic diagnosis and medicinal discovery.During the past decades,impressive progress in sensor-based detection systems with features of effectiveness,high sensitivity and high selectivity,such as capillary electrophoresis analysis(CE),high performance liquid chromatography(HPLC),UV-vis,fluorescence spectroscopy(FS)has been made.Compared to other imaging modalities,fluorescence imaging offers high spatiotemporal resolution as a largely non-invasive technique.It can probe the deeper layers of a specimen at ambient conditions and also enable spectroscopic diagnosis with chemical sensitivity.The core of fluorescence-based sensing methods is the fluorescence probes.It has been rationalized that the requirements for high performance fluorescence probes include the following characteristics: strong fluorescence signal,good biocompatibility and high sensitivity.Generally,the detection mechanism of the fluorescent probes include fluorescence enhancement(turn-on),fluorescence quenching(turn-off)and fluorescence resonance energy transfer(FRET)and so on.These mechanisms largely depend on the changes of fluorescence intensity and emission wavelength which caused by the targets quantity.However,in many cases,these methods are non-specific or underwent tedious bio-conjugation.Thus,it is urgent and of importance to develop new detection mechanisms utilizing special reactions to achieve high selectivity detection.After carefully scanning the literatures,we found that fluorescent emission from organic semiconductors with donor-acceptor(D-A)structure are very sensitive to the D-A pair due to intramolecular energy transfer impart high influence on their optical absorptions and emissions.However,this unique fluorescence properties of these D-A dyes are seldom used fluorescence sensing systems.In this end,we put our eyes on developing dyes with specific reaction group which can finely tune the ICT effect along the whole conjugated skeleton,finally leading to sensitive fluorescent signal changes.To evaluate our design principles,this paper intends to design three kinds of different conjugated organic molecule fluorescence probes toward nitric oxide(no),cysteine(Cys)and hydrogen peroxide(H2O2),respectively.It is expected that our results can open new opportunities for fluorescence imaging or sensing in future biological and medical research.This thesis mainly includes the following three sections:(1)Phthalate diamine-fluorene-based NO probe.This probe was synthesized via a straightforward strategy of Suzuki coupling with subsequent reduction of benzo[2,1,3-b]thiadiazole.All intermediates and dye are fully characterized.The photophysical properties of the probe were investigated with UV-vis and fluorescence.The probe exhibits specific and high-speed response to nitric oxide in aqueous and in cells.As predicted by the DFT calculation,the absorption maxima and emission maxima of the probe were both changed dramatically in wavelengths and intensities by reacting with NO.The rationality and feasibility of the design of the fluorescent probe were verified by the characterization of the time of flight mass spectrometry.Through molecular simulations confirm the this strategy the theoretical feasibility and accuracy: when faced with nitric oxide molecular probes,ortho aromatic diamine and no molecule occur intramolecular formation triazole structure,so that the electron rich aromatic amine transformation into a weak electron donating properties,the fluorescence enhanced.Therefore,it can recognition specificity of nitric oxide.Confocal fluorescence imaging on Hela cell lines were also studied.(2)PET dyes based on the reaction pair of maleimide and cysteine.Perylene,a five benzene-fing fused polycyclic aromatic hydrocarbon,always exhibits high fluorescence intensity.When maleimide group was introduced to the periphery of perylene,the probe itself shows illegible fluorescence emission.By after the “click” reaction with cysteine,Michael addition reaction happens between maleimide and cysteine,thus,the PET process is destructed,which leads to significant enhancement of fluorescence emission by 135 times.Both quantitative analysis and confocal fluorescence imaging in cells were studied.The results indicate this dye design strategy is effective and feasible.(3)hydrogen peroxide-targeted perylene monoimide dye with boric acid ester.To specifically detection hydrogen peroxide,a new near-infrared dye with perylene monoimde as the fluorogen was designed.Due the poor solubility in common solvents and the high polarity,it is failed to obtain this probe with sufficient magnitude and quality.After tried for many entries,only few of final product was obtained,and the chemical detection of H2O2 was not conducted at this moment.Although failed,it is helpful for us to propose new dyes for this project.