Synthesis Of Rhodamine-Naphthalimide Derivatives And Photophysical Properties Of Fluorescent Probes

In recent years, the ratiometric fluorescent probe based on fluorescence resonance energy transfer (FRET) has become a research focus. In this paper, based on the design principle and information transmission mechanism of the ratiometric fluorescent probe, a series of rhodamine-naphthalimide ratiometric probe RNAM, RENA and RENO were designed and synthesized, in which the naphthalimide has superior aggregation-induced emission (AIE) behavior and the rhodamine has the sensitive "off-on" process. The fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET) have been design to the same molecule. The rhodamine-naphthalimide dye exhibited the significant enhancement of aggregation-induced emission (AIEE) properties. At the same time, the silica nanoparticles loaded with the AIE fluorescent dyes were prepared and their spectral properties were studied preliminarily. The selective recognition toward metal ions and the response to pH was investigated in the rhodamine-naphthalimide probe. While a possible duel-site recognition mechanism was proposed. In addition, the double-channel fluorescence images of Hg2+ ions in living cells further certified the potential value of the rhodamine-naphthalimide dye. The specific contents were as follows:1.1,8-naphthalimide and rhodamine B were selected as fluorophores. A series of rhodamine-naphthalimide ratiometric probe RNAM, RENA and RENO were designed and synthesized, in which hydrazine hydrate or ethylenediamine was selected as the spacer between the two fluorophores. N, N-dimethylethylenediamino and O-methylethoxy were selected respectively as the 4-position terminal structures of naphthalimide to achieve dual-switch states. All compounds were well characterized by melting point,1HNMR,13C NMR, MS and HRMS techniques.2. The enhancement of aggregation-induced emission of rhodamine-naphthalimide dye RNAM, RENA and RENO were measured. Dye RNAM, RENA and RENO in solid state emitted strong fluorescence and the emission peaks were 576,549 and 550 nm, respectively. In different water contents of the ethanol/water mixture solution, the fluorescence intensity first decreased and then increased with the increase of water content and the emission wavelength exhibited red-shift. The maximum emission wavelengths at 90% of water content were 559,542 and 560 nm, respectively. The fluorescence intensity of dye RNAM at 90%of water content is 12 times that of 70%. The effect of the different spacer and 4-position terminal structures on AIEE properties was discussed.Then, the silica nanoparticles RNAM/SiO2, RENA/SiO2 and RENO/SiO2 loaded with the AIE fluorescent dye were prepared. Transmission electron microscopy images showed that these nanoparticles had good solubility and stability in water, and the spherical diameter is about 60 nm. The fluorescence emission wavelengths of these nanoparticles in water were 495,500 and 419 nm, respectively.3. The selective recognition toward metal ions and the response to pH value of the rhodamine-naphthalimide probe RNAM, RENA and RENO were investigated by fluorescence spectroscopy. The probe RNAM and RENA showed the high sensitivity and selective recognition of Hg2+ ions; probe RENO had the response to Sn4+, Sn2+ and Zr4+ multiple metal ions. The results indicated that the 4-site substituted groups had a great influence on the selectivity and fluorescence properties. Binding of Hg2+to the dye RNAM inhibition the photoinduced electron transfer process of naphthlimide moiety and induced the intramolecular fluorescence resonance energy transfer from the donor naphthalimide to the acceptor rhodamine. This provided a new effective platform for the design of the ratiometric fluorescent probe. And the dual-switch states and the possible mechanism in the identification process were discussed. In addition, the response to H+ of the rhodamine-naphthalimide probe was found.4. In addition, the double-channel fluorescence images of rhodamine-naphthalimide dye RNAM, RENA and RENO toward Hg2+ ions were studied in living cells. The rhodamine-naphthalimide dye was successfully applied to the recognition of metal ions in living cells, which further certified the potential application prospect of the rhodamine-naphthalimide dye.