Design, Synthesis And Applications Of Benzoxazole-derived Fluorescent Probes Based On ESIPT Strategy

In recent years, fluorescence technique obtains a wide range of applications, for their simple operation, high sensitivity, good selectivity, wide linear range and real time detection. Fluorescent sensors based on excited-state intramolecular proton transfer(ESIPT) has recently received considerable attention due to its high fluorescence quantum yield, dual fluorescence intensity changes and large Stokes shift. These characteristics could be sufficient to avoid self-absorption and inner-filter effect. 2-(2’-Hydroxyphenyl)benzoxazole(HBO), a typical ESIPT molecule, has been widely used to design novel and promising fluorescence probes. In this thesis, HBO-based fluorescence probes for zinc ion, hydrazine and ATP detection were successfully designed and synthesized.Highly selective fluorescent probes for Zn2+ based on benzoxazole derivatives and ESIPT strategy have been readily synthesized. This is the first demonstration that introduction of substituent to fluorescent signal moiety rather than direct sensing unit enhances sensitivity and selectivity. Fluorescent molecules with different substituent modification on 5-position showing different extents of fluorescent response to Zn2+. Fluorescent probes with different substituent modification on 3’-O-substituted showing different fluorescent response to Zn2+ and Cd2+. Instead of sophisticated tuning of recognition units, simple substitution varied on fluorophore subunit provides a new strategy for design of metal ions fluorescent sensors.Adenosine 5’-triphosphate(ATP) is a functional molecule associated with many important biological processes. Detection of the ATP concentration level in vitro and in vivo is thus important for the study and understanding of these real-time biological processes. A novel Ga3+ self-assembled fluorescent sensor based on the ligand of 2-(2′,3′-dihydroxyphenyl)benzoxazole has been designed. It can selectively recognize ATP with fluorescence enhancement from ADP, AMP and other structurally similar nucleoside triphosphates(GTP, TTP, CTP and UTP) in vitro and in vivo. The detection limit for ATP was calculated to be 5.49×10-7 M, which is much lower than that of intracellular concentrations(1–10 mM). Inaddition, DHBO–Ga3+ can be applied to detect ATP-relevant enzyme activity.In this thesis, we present a novel and high selectivity hydrazine fluorescent probe, where its 5’-hydroxyl functions to activate aldehyde group for hydrazine addition and capture hydrazine through inter- and intramolecular hydrogen bonding to fasten response. The detection limit of probe to hydrazine was found to be 2.7 ppb, which falls below the 10 ppb limit set by EPA.This probe can detect hydrazine in both solution and gas state by color changes from readily prepared strips. Furthermore, it was found that the probe is able to detect hydrazine in Hela cells.