Synthesis And Application Of Novel Fluorescent Probes With Long Emission Wavelength Based On BODIPY Dyes

BODIPY derivatives are the kind of popular fluorescence dyes because they possess relatively large absorption coefficients, high fluorescence quantum yields, excellent chemical and photostability attributes and easy modification. The maximum absorption wavelength of BODIPY is about 500 nm. BODIPY emits green fluorescence. After modification, the maximum absorption wavelength usually can reach above 550 nm and emission maxima ranges from orange to red or even the near-infrared region. Fluorescent probes with long absorption and emission wavelength have prominent advantages in actual detection. We mainly finished several works as follows:Firstly, we modified the position of 3, 5 at the core of BODIPY by introducing phenol through carbon-carbon double bond in order to extend the conjugate structure. On one hand, the introducing of phenol which was an electron-donating group could make the absorption and emission wavelength red-shift, on other hand the oxygen atom of the hydroxyl groups that was the recognition group can complex with Fe3+. So, we designed a novel small molecule fluorescent probe(L) based on BODIPY for selective detection Fe3+ with the property of fluorescence turn on. L had a maximum absorption peak at 571 nm and emitted orange fluorescence(602 nm) in alcohol solution. After addition Fe3+ in L alcohol solution, a dramatic color changed from pink to yellow, allowing the colorimetric detection of Fe3+ by the naked eye. 27-fold increase in fluorescence intensity at 530 nm when it reached balanced titration. The sensing mechanism was Fe3+ formed complexes with L via coordination with the 4-hydroxystyryl moiety. The binding of Fe3+ with the lone pair on the oxygen atom in L resulted in a reduction of the electron donating ability of the oxygen atom of 4-hydroxystyryl group which was in conjugation to the BODIPY core. This suppressed the ICT process causing the blue shift of the absorption spectrum band and an enhancement of the fluorescence. Finally, the cellular imaging indicated that L was successfully endocytosed by cell lines and had good cell membrane permeability. What’s more, L can be explored for monitoring Fe3+ within living cells.In addition, the hydrogen atom of the hydroxyl groups were the recognition group can interact with F-. In the solution of acetonitrile, upon addition of F-, the phenol moiety was electron-rich via deprotonation and engaged in photoinduced electron transfer quenching of the BODIPY excited state. Upon interaction of L with F-, two new absorbance peaks emerged at 402 and 683 nm. Meanwhile, the absorbance peaks at 337, 528 and 565 nm were greatly decreased. At the same time, a visually detectable color change from pink to indigo, allowing the colorimetric detection of F- by the naked eye. The reversibility and reusability of L for sensing the F- had been demonstrated by sequential addition of F- followed by TFA over four cycles, indicating L could be used as a reversible and reusable probe for F-.Secondly, considering that the conjugated polymers have fluorescence signal amplification, high sensitivity, high selectivity, low detection limit, real-time monitoring and easy operation, the conjugated polymer(P1) containing alkynyl fluorene and BODIPY moieties was successfully synthesized by sonogashira coupling reaction. Due to extend the conjugate structure and the small steric hindrance, the emission maxima achieve deep red region. P1 could allow selective detection of F-and CN- simultaneously by distinct color and fluorescence changes among a series of ions. When P1 reacted with F-or CN-, a dramatic color changed from purple to orange and faint yellow, respectively, allowing the colorimetric detection of F- and CN- by the naked eye. 74.1 fold increase in fluorescence intensity at 579 nm to yield emission color change from red to yellow in presence of F-. On the other hand, the 43.6 and 104.2fold fluorescence enhancements at 514 and 563 nm resulted in emission color change from red to greenish yellow in presence of CN-. To gain further insight into the nature of P1–CN- and P1–F- interactions, we monitored the changes of 11 B, 19 F and 1H NMR spectra produced via the addition of CN- or F- to compound 3-4 solution. The mechanism was the hybridized boron center is prone to nucleophilic displacement. It is likely for fluoride and cyanide to disrupt the ring through complexation with the central boron atom. So, addition of fluoride and cyanide result in detachment of stable bridges, due to a nucleophilic displacement to break a B-N bond yielding some different compound and presenting a different spectral and color change. Finally, cellular imaging indicated that P1 was successfully endocytosed by cell lines and had good cell membrane permeability and could be utilized as a fluorescent probe for cells.In addition, cationic conjugated polymers both have traditional conjugated polymers optical and electronic functions and good water solubility of the polyelectrolyte. Considering that the importance of DNA, we got the cationic polymer P2 after ionizing the side chain of P1. P2 could allow selective and sensitive detection of DNA. The electrostatic interaction between P2 and negatively charged DNA formed the P2/ DNA aggregation. The maximum reductions of the absorption peak intensity were 27.2 % at 360 nm and 27.5 % at 574 nm for P2 with the DNA concentrations of 6×10-5 M. At the same time, the maximum reduction of the red fluorescence intensity was 66 % at 648 nm. DNA detection limit concentration for P2 was 1×10-13 M, which may have a potential application in the detection of DNA. Cellular imaging results indicated P2 could be utilized as a fluorescent probe for cellular imaging of cells.Thirdly, BODIPY is similar to porphyrin. Both of them have the structure of pyrrole and the synthetic methods are similar. On one hand, considering the porphyrin macrocyclic may have longer absorption and emission wavelength, on the other the detection sensitive of conjugated polymer, we designed and synthesized conjugated polymers(P6) containing porphyrin units. P6 could allow selective and sensitive detection of Con A by specific mannose/Con A binding. The distance between P6 was substantially shortened in the presence of Con A due to the specific mannose/Con A binding, leading to occur FRET that was energy transfer from poly(fluorene–phenylene)(energy donor) to porphyrin(energy acceptor) unit. In the presence of 10-6 M Con A, the 57% of blue poly(fluorene–phenylene) fluorescence at 456 nm is quenched, while 5.3 fold increase of red fluorescence of porphyrin segment at 625 nm is present. The selectivity of detection was also investigated using nonspecific proteins that could not occur FRET, pronounced selectivity was observed only for Con A. P6 showed slow cytotoxicity by CCK-8 assay, which made its potential application as fluorescent agent for cellular imaging.