Design, Synthesis And Fluorescent Properties Of Novel Fluorescent Probes Based On Bodipy And Porphyrin Dyes

Owing to the excellent characteristics such as high sensitivity, better selectivity, as well as the ease of signal transmission nature, fluorescent probes have been widely applied to the fields of chemistry, biology, materials, medicine and so on. Among multitudinous chromophores, Bodipy and porphyrin have been revealed as the more attractive fluorescent signaling unit, associated with their favorable characteristics such as pronounced photostability, high extinction coefficient, narrow emission band, high fluorescence quantum yield. Taking this into accounts, a series of fluorescent probes with the excellent Bodipy or/and porphyrin signaling units and the efficient 8-HQ or/and DPA receptor have been designed and synthesized, and their recognizing functions for different tested targets have been systemically investigated through the optical measures. Our research work has been focused on the following respects:1. The study of Bodipy derivates based on 8-hydroxyquinoline moiety:OFF-ON-OFF type of pH fluorescent sensorsThe construction for high efficient fluorescent sensor is to conjugate a suitable fluorescent signaling unit with a receptor for targets to be detected. Bodipy, as an excellent signal unit, has been widely employed in constructing fluorescent sensors towards heavy-metal ions, pH, solvent polarity, and small molecules. As for the recognizing group, the 8-hydroxyquinoline moiety (8-HQ) with unique pyridyl N and-OH structural nature can be employed not only as functional receptor for metal ions, but also as the pH indicator for both acidic and basic systems due to its weak acid or base character under protonated or deprotonated form, respectively. Thus, four novel 8-hydroxyquinoline-substituted boron-dipyrromethene derivatives, namely 4,4-difluoro-8-(5-(8-hydroxyquinoline))-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (1),4,4-difluoro-8-(5-(8-hydroxyquinoline))-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (2),4,4-difluoro-8-(5-aza-styryl-(8-hydroxyquinoline))-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (3), and 4,4-difluoro-8-(5-aza-styryl-(8-hydroxyquinoline))-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (4), were designed and synthesized. As expected, the intense fluorescence of compounds 1,2, and 4 has been revealed to change depending on the pH value, which gradually gets diminished along with either decreasing or increasing the pH value of their solution in mixed solvent of H2O and acetonitrile (1:9) due to the protonated quinolinium NH+～-OH form and deprotonated quinolinate N～-O- form of the 8-HQ moiety under acidic and basic conditions, respectively. This in turn leads to a photo-induced electron transfer from excited Bodipy moiety to 8-HQ unit under acidic condition and just a reverse electron transfer process under basic condition responsible for the gradual fluorescent quenching in the acidic and basic systems. As a consequence, these compounds seem to represent the first example of novel OFF-ON-OFF type of pH fluorescent sensors, which will be helpful for developing novel versatile fluorescent pH sensors with potential applications in chemical and biological fields.2. Porphyrin derivate with DPA recognizing group:the versatile fluorescent sensors for Cu2+ and Pb2+.Porphyrin derivates are provided with the excellent optical properties including high fluorescence quantum yield, large Stokes'shift, relative long excitation and emission wavelengths (> 400 nm and 600 nm, respectively), as well as the facile modification on the twelve replaceable positions of porphyrin ring, which give birth to a wide variety of porphyrin derivates with different function. As a result, porphyrin unit, as an excellent signal unit, have been used in detecting for metal ions, anions and neutral molecules. Based on porphyrin signal unit, we synthesized one novel fluorescent probe with DPA recognizing unit, namely Porphyrin-DPA. Among all tested metal ions, only when Cu2+was added, the intense fluorescence from the porphyrin subunit was revealed to get remarkably diminished, even completely disappeared. Reversely, the absorption spectra of this compound only show favorable response to the addition of Pb+:along with the addition of Pb2+, the absorbency at the 418 nm gets decreased and the new emerging absorption of porphyrin-Pb2+ at 468 nm gradually gets increased. This reverse absorbency change and large wavelength shift between these two absorptions endow porphyrin-DPA the excellent detecting potential for Pb2+. Metal selective experiments indicate that Porphyrin-DPA still shows preferable selectivity for Cu2+/Pb2+ despite the coexistence of Cu2+/Pb2+ with the other metal ions. Thus, porphyrin-DPA can be utilized as both the ratio sensor for Pb2+ and "ON-OFF" fluorescent sensor for Cu2+, respectively. 3.8-Hydroxyquinoline-benzoate-linked Boron-dipyrromethene and porphyrin dyad: versatile fluorescence resonance energy transfer ratiometric sensor for Hg2+ and Fe2+Boron-dipyrromethene (Bodipy) and porphyrin moieties have been utilized not only as a singly fluorescent signal unit, but also synchronously as the energy donor and acceptor in the dyad systems due to their favorable overlap between the Bodipy emission and the porphyrin absorption spectra. Moreover, the flexible 8-hydroxyquinoline-benzoate (8-HQ-B), which not only facilitates the energy transfer process, but also exhibits the better binding affinity for cations, can be employed as a bridge receptor. Thus, in the third section of this paper, a flexible 8-hydroxyquinoline-benzoate(8-HQ-B)-linked Bodipy and porphyrin dyad, namely Bodipy-(8-HQ-B)-porphyrin has been designed, synthesized, and characterized by 1H NMR, 13C NMR, and mass spectroscopy in addition to elemental analysis. As expected, in this compound, the energy is efficiently transferred from the Bodipy unit to the porphyrin group, and the energy transfer efficiency between Bodipy and porphyrin moieties is dependent on the combination of 8-HQ-B with different metal ions:the combination with Fe2+ inhibits intramolecular energy transfer, leading to the increase of Bodipy emission (516 nm) and the decrease of porphyrin emission (650 nm), as well as the corresponding increase in F516/F650 signal ratio; by contrary, the combination with Hg+ promotes intramolecular energy transfer, giving the decrease in F516/F650 signal ratio. The present result appears to represent the first example of versatile FRETRMS for various cations, which will be helpful for the design and synthesis of novel fluorescence resonance energy transfer ratiometric sensor with potential applications in chemical and biological fields.