Design, Synthesis And Properties Of Novel Fluorescent Probes Based On Perylene Diimide And Naphthalimide

Fluorescent probes for sensing and monitoring chemical analytes are a topical and attractive field for chemistry, biology and environmental science due to their high sensitivity and simplicity. Developing highly effective fluorescent probes is thus a fundamental task for organic and analytical chemists.Perylene tetracarboxylic diimides (PDIs) are attractive molecular building blocks that are currently being extensively investigated for use in a variety of photoactive organic materials, such as organic field-effect transistor (OFET), light-harvesting solar cells, light emitting diodes. These dyes have recently generated great interest in the field of photonic materials, because of their excellent thermal and photo stability, high luminescence efficiency, easy modification on the molecular structure,, and desirable optical and redox characteristics. PDIs are good electron acceptors with low reduction potential. Therefore PDIs are promising candidates for the application as fluorophores in fluorescent probes based on photoinduced electron transfer (PET).In the first part of our research, two novel "turn-on" fluorescent probes with PDI as the fluorophore and two different di-(2-picolyl)-amine (DPA) groups as the metal ion receptor (PDI-1 and PDI-2) were successfully synthesized with satisfactory yields. PDI-1 exhibited high selectivity toward Ni2+ in the presence of various other metal cations including Zn2+, Cd2+ and Cu2+ which were expected to interfere significantly. A 1:2 stoichiometry was found for the complex formed by PDI-1 and Ni2+ by a Job's plot and by non-linear least square fitting of the fluorescence titration curves. The binding constant Ka was determined to be 2.7×109 M-2 through the Benesi-Hildebrand analysis. By introducing an extra diamino ethylene group between DPA and the phenyl bridge, the receptor was modified and the high selectivity of the PDI-based fluorescent chemosensor shifted to Fe3+ from Ni2+. The enhancement factor of fluorescence response of PDI-2 to Fe3+was as high as 138. The results of ESI MS showed that the stoichiometry of the complex between PDI-2 and Fe3+ in N, N-dimethylformamide (DMF) was 1:2. The binding behavior of the receptors in these two compounds is affected significantly by the PDI fluorophores. Most interestingly, both Ni2+ and Fe3+ are paramagnetic metal ions, which are known as fluorescence quenchers and are rarely targeted with turn-on fluorescence probes. This result suggests that PDTs are favorable fluorophores for a "turn-on" fluorescence probe for paramagnetic transition metal ions because of the high oxidation potential.4-amino-1,8-naphthalimide derivatives are also excellent fluorescence dyes like PDIs. Due to their remarkable luminiscent properties, they have found increasing applications in a number of areas including colouration of polymers, fluorescent solar energy collectors, liquid-crystal additives, electro-optically sensitive materials, fluorescent markers in medicine and biology and ion probes. Especially, they absorb and emit in the visible range with large Stokes'shift, high fluorescence quantum yield, and they have the advantages of high photostability, simple structure and easy approaches to modification, which are favorable properties for the design of fluorescent chemosensors.In the second part of our research, based on the strategy of intramolecuar charge transfer (ICT) two novel fluorescent probes using 4-amino-1,8-naphthalimide as fluorophore and dipicolylamine as receptor for metal cations were successfully synthesized and characterized through 1H NMR,13C NMR, ESI-MS and MALDITOF-MS. Both of them showed high selectivity towards Cu2+ in acetonitrile-aqueous (8:2) mixture at room temperature. Addition of Cu2+ to Nal-1 or NaI-2, a 80 nm blue shift of the absorption maximum produced because of complexation between probes and copper ions, which resulted in the reduced ICT effect. The fluorescence of fluorophore was almost quenched in stark contrast to other metal ions. The results of DFT calculation based on B3LYP/6-31G* level indicated the charge transfer from the excited naphthalimide moiety to Cu2+ center was responsible for the remarkable fluorescence quench. Via Job's plots and non-linear least square fitting of the absorption titration curves,1:1 and 1:2 stoichiometry were found for the complex formed by Nal-1 and Cu2+, Nal-l and Cu2+, respectively. The binding constant Ka and Ka' were determined to be 4.5×104 M-1 and 3.12×109 M-2, respectively through Benesi-Hildebrand analysis. Based on the results of part 2, new compound N-p-(N'-2-(N",N"-di(2-pyridylmethyl) amino-ethylene) aniline)-4-N"'-di (2-pyridylmethyl) amino-1,8-naphthalimide (NaI-3) was successfully synthesized and characterized through 'H NMR,13C NMR and ESI MS. Addition of Zn2+ to NaI-3 in acetonitrile produced a 50 nm blue shift of absorption maximum, while the fluorescence quantum yieldΦduring the titration of zinc ions was remarkablely increased from 0.09 to 0.60. Both of them attributed to the formation of a NaI-3/Zn2+ complex, which resulted in a decreasing ICT effect and the inhibited PET process. On the other hand, addition of Cu2+ to NaI-3 in acetonitrile produced an 80 nm hypsochromic shift of absorption maximum, while the fluorescence quantum yieldΦwas dramastically decreased from 0.09 to 0.01, which was caused by the reduced ICT effect and ligand to metal charge transfer (LMCT) process, respectively. While addition of the equal equivalence of Cu2+ to the NaI-3/Zn2+ complex system, the quantum yield of fluorescence decreased from 0.6 to 0.2. Compound NaI-3 described here could be considered to perform an integrated circuit function with one AND and one NOT, which could be interpreted by a two-input INHIBIT logic gate. The present results demonstrated an efficient way for elaborating and transmitting information at a single molecular level and will be useful for further molecular design to mimic the function of the complex logic gates.