| Red-emitting AIE(Aggregation- induced emission)-active fluorescent moleculars are desirable materials in bio-sensing. On the one hand, AIE moleculars overcome the aggregation-caused quenching(ACQ) phenomenons of traditional probes and enhances the sensing sensitivity. O n the other hand, red-emitting moleculars possess deep tissue penetration and minimal photo-damage to living cells. Therefore, it’s of significance to develop red-emitting AIE-active fluorescent probes. In this study, a series of AIE-active red-emitting moleculars and polymers based on d iketopyrrolopyrrole are synthesized and characterized. Moreover, their photophysical properties as well as application in bio-sensing are investigated.Firstly, conjugates DPP1 and D PP2 are synthesized based on anthracenone and diketopyrrolopyrrole.The introduction of anthracenone favors the red emission of moleculars and successfully converts d iketopyrrolopyrrole from ACQ to AIE property. The emission intensity of DPP1 containing two diethylamino groups in side chian in H2O/THF mixture(9:1, v/v) is 13.7 times higher than that in pure THF. Making ues of the AIE property of D PP1 and the protonization or deprotonization of diethylamino groups, DPP1 can serve as a p H probe in THF/H2O(7:3,v/v). In acid solution, D PP1 is protonized and has enhanced water solubility. As the result, the DPP1 moleculars readily disperse in the solution and the emission is weak. While in basic solution, D PP1 is deprotonized and the water solubility of DPP1 decreases, which leads to the rapidly aggregation of the moleculars. Owing to the AIE property of DPP1, the emssion becomes stronger after aggregation. At a p H of 12.36, the emission intensity of DPP1 is 6.67-fold compared to that at p H 2.53. On the other hand, DPP2 is an ammonium-salt containing compound and has no AIE phenomenon in solution, but shows emission enhancement in solid state and in the increasing viscosity system. BSA has a negative charge(the isoelec-tric point is about 4.7) in water medium at neutral p H and its structure contains many hydrophobic cavities. Consequently, due to electrostatic and hydrophobic interaction, positive D PP2 can form aggregates with BSA to amplify its emission with 7.65- fold fluorescence enhancement in presence of 100 μM BSA. Therefore, DPP2 is a fluorescent “turn on” biological probe for BSA detection. In addition, D PP2 can be utilized as a fluorescent probe of low cytotoxicity for cellular imaging of He La cells, where red fluorescence is observed in the cytoplasm.Based on the last work, a novel AIE-active diketopyrrolopyrrole(DPP) derivative containing anthranone and para-iodophenyl units(Monomer 1) is synthesized. Monomer 1 can be polymerized with 2,7-diethynyl-9,9-bis[6’-(N,N-diethylamino)-octyl]fluorine through Sonogashira reaction and ionized to yield cationic polymer P1, where AIE-acitve DPP and ACQ-active fluorene units are linked together with a flexible alkyl spacer. P1 emits purple fluorescence with two emission peaks at 440 and 625 nm in DMSO and is AIE- inactive due to its amphiphilic performance and the presence of ACQ-active fluorene unit. The introduction of fluorene and the formation of polymer significantly improve the sensing selectivity of BSA. The recognition of BSA is conducted in DMSO/PBS buffer(v/v = 1/1). P1 aggregates in DMSO/PBS buffer(v/v = 1/1) and generates strong π-stacking interactions,thus give rises to the redder and weaker emission of P1. In presence of BSA, owing to the special structure of BSA and the presence of flexible alkyl chain, the fluorine and DPP units in P1 can respectively react with the hydrophobic cavities of BSA. As a result, the π-π stack between fluorine and DPP is relieved and P1 is disaggregated with enhanced emission Therefore, P1 can realize the turn on dectetion of BSA. The fluorescence intensity of P1 at 450 and 645 nm is increased by 2.94 and 2.11- fold when the concentration of BSA increased to 70 μM. The particular structure of BSA and the hydrophobic interaction play critical roles in the process of recognition, thus P1 show excellent selectivity for BSA. Other anions, negative ATP, DNA or proteins such as Con A and Pep do not have significant effect on the emission of P1.In addition, P1 possess low cytotoxicity and can be utilized as a fluorescent probe for cellular imaging.Though Suzuki reaction, a red-emitting electron donor-acceptor polymer(N2) containing diketopyrrolopyrrole as electron acceptor and triphenylamine as electron donor has been designed and synthesized. Due to ICT process, N2 is shown to possess the remarkable solvatochromism property and the spectral behavior vary with the solvent. N2 exhibit typical AIE property with 7-fold fluorescence enhancement in DMF/H2O(1/9, v/v) compared to that in pure DMF. Additionally, N2 is extremely sensitive to water in THF。The fluorescent intensity of N2 decreased dramatically when the water content was below 2.00%(v/v): the reduction in relative fluorescence intensity reached nearly 53%. Particularly, the fluorescent intensity of N2 as a function of water content showed a good linear relationship below 2.00%(v/v), and the detection limit of N2 for water is determined as 0.005%. So, N2 is able to serve as a sensitive fluorescent indicator for the qualitative and quantitative detection of low-level water in THF. Moreover, the quaternization of N2 by C H3 I gives ammonium- salt P2. The emission intensity of P2 in glycerol/DMSO mixture(9:1, v/v) is about 1.15- fold higher than that in DMSO. Similarly, the intrinsic weak fluorescence of P2 in DMSO/PBS(1:1, v/v) increases to 1.9- fold after addition of 100 μM BSA through electrostatic complexation and hydrophobic interaction.Finally, a Schiff base D PP3 based on diketopyrrolopyrrole and 1-naphthylamine is designed and synthesized. DPP3 works as a difuctional probe which realizes the sequence detection of HSO4-and Fe3+ via a fluorescence “off-on-off” mechanism for the first time. The introduction of 1- naphthylamine extenst the conjucgation and favors the red emission. Moreover, the formation og C=N favors the photoinduced electro n transfer process, which lead to the weak emission of D PP3. In presence of HSO4-, DPP3 hydrolysizes to generate emissive compound 5-1, companied with color changing from red to orange and 10.6 fold fluorescence enhancement. Therefore, DPP3 serves as a “turn-on” chemodosimeter for HSO4-. The in situ system generated from D PP3+HSO4- contains of several binding sites and thus be able to further interact with Fe3+ to form weak fluorescent complex with color change from orange to colorless. Hence, DPP3+HSO4- works as a “turn-on” chemodosimeter for Fe3+. Moreover, other anions or metal ions fail to generate distinct response, which indicats that DPP3 has desirable selectivity for relay recognition of HSO4-and Fe3+. DPP3 also functions when supported by silica, indicating that probe DPP3 has the potential for working as optical solid sensors. |
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