The Synthesis And Properties Of Based On The Benzimidazo [2,1-a] Benz [de] Isoquinoline-7-one Derivertives

In the paper,four fluorescent probes based on benzimidazo[2,1-a]benz[de]isoquinoline-7-one as a fluorophore via introducing different receptors were designed and synthesized,including benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12 carboxylic acid（L1）,ethyl（Z）-2-（hydroxyimino）-2-（2-（benzimidazo[2,1-α]benz[de]iso quinoline-7-one-12-carboxamido）thiazol-4-yl）acetate（L2）,（benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carbonyl）glutamic acid（L3）,（benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carbonyl）aspartic acid（L4）.These structures of compounds mentioned above and their intermediates were all characterized and verified by 1H NMR,13 C NMR,MS and FTIR spectrums.Moreover,the optical properties of four probes were all further investigated by UV-vis absorbance and fluorescence emission spectra.The four fluorescent probes exhibited good optical properties towards different metal ions and their metal complex acted as secondary sensors for PPi.L1 showed excellent selectivity to Hg2+ in fluorescence emission spectra in CH3CN/H2O（v/v=1:1,pH=7.2）aqueous solution,and was a “turn-on” fluorescent probe.L1 was confirmed to be reversible for Hg2+ though the mutual addition of Hg2+ and PPi to the solution of L1 for several times.Furthermore,the fluorescence intensity of L1 varied with the solution pH value.Under acid condition,the formation of one hydrogen bond prevented the PET process and L1 emitted remarkable fluorescence.Under basic condition,L1 was deprotonated and PET processrecovered,so there was no fluorescence.In addition,the 1:1 stoichiometry between L1 and Hg2+ was obtained by Job’s plot.L2 showed significant fluorescence enhancement towards Fe³⁺ in the presence of other competitive metal ions due to the group of ethyl（E）-2-（2-aminothiazol-4-yl）-2-（hydroxyimino）acetate.In CH3CN/H2O（v/v=9:1,pH=7.4）buffer aqueous solution,the detection limit of probe L2 to Fe³⁺ was up to 10-8 M.Correspondingly,the solution colour of L2 changed from pale green to bright green after Fe³⁺ was added.Besides,MS titration experiment of L2 to Fe³⁺ showed the 1:1 stoichiometry.In purely aqueous solution,L3 exhibited fluorescence decreasing towards Fe³⁺ and Al³⁺ at the same time.However,Fe³⁺ can be distinguished from Al³⁺ though further study.3 equivalents of Fe³⁺ induced the fluorescence emission quenching completely,but 5 equiv.of or more Al³⁺ only caused the emission intensity decreasing by 72 %.The result indicated the greater affinity between L3 towards Fe³⁺ than Al³⁺.What’s more interesting,the fluorescence intensity L3 increased gradually upon incremental addition of pH valuesfrom 2.0 to 7.4 and maintained relative stability in the pH range of 7.4-11.0.At pH > 11.0,the fluorescence intensity of L3 decreased rapidly and was almost equal to that at pH value 2.0.Based on the experimental results,three different existing formations L3、L3-and L32-were proposed.They were in accordance with acid condition,neutral condition and strongly basic condition,respectively.Under neutral condition,two hydrogen bonds formed in L3-and the maximum of fluorescence intensity was observed due to the inhibition of PET process.And DFT/TDDFT calculations also supported the experimental phenomenon.In addition,Job’s plot indicated the 1:1 binding stoichiometry between L3 and Fe³⁺ or Al³⁺.The optical properties of L4 to metal ions were similar to that of L3 due to the similarity in chemical structure of L4 and L3.However,the maximum in fluorescence intensity of probe L4 was higher than L3.