Fluorescent Sensors Based On Diketopyrrolopyrrole And Quinacridone Derivatives

Fluorescent chemosensors, regarded as a low-cost and high sensitivity device, is receiving more and more attention from chemists and biochemists. Simple chemosensors comprise of a signal output subunit and several recognized units. Recently, most studies of fluorescent sensors have focus on designing and constructing different recognized units, but there have been relatively few studies on finding new signaling units. Diketopyrrolopyrrole (DPP) and quinacridone (QA), also known as two high performance dyes, have been extensively studied because of their outstanding photoelectric properties as well as light and thermal stabilities. However, the DPP and QA derivatives were seldom reported as signal output subunits in the fluorescent chemosensor devices.In this thesis, we describe rational design of series of DPP and QA derivatives as new fluorescent chemosensors. Four DPP-based compounds, DPP 1～4, were studied as ratiometric sensors for fluoride ion and two QA-based chemodosimeters, TQA1-2, were worked in turn-on manner for the sensing of mercury ion. Furthermore, two series of conjugated polymers as PDPP1 and PTQA1～5 were synthesized through Suzuki couple reaction. The triphenylamine-based sensors, TPA1 and PTEPA2, were also designed and synthesized for sensing cyanide and mercury ions, respectively. All of the sensors above were characterized by 1H NMR,13C NMR, HRMS spectra while the photophysical and sensing properties were also studied. The main contents and results are summarized as follows:In charpter 1, major sensing principles of optical chemosensors and the designing of two-photon sensor are introduced, and the recent process of fluorescent chemosensors is reviewed. Then the research strategy of the dissertation is presented.In charpter 2, the hydrogen bond receptor for detecting fluoride ion was introduced and three new diketopyrrolopyrrole (DPP) compounds DPP 1-3 are shown to be colorimetric and ratiometric fluorescent sensors for fluoride anions with high sensitivity and selectivity. The recognition mechanism is attributed to the intermolecular proton transfer between a hydrogen atom on the lactam N positions of the DPP moiety and the fluoride anion. For DPP 1-3 in DCM, the addition of fluoride results in vivid orange-to-red absorption color change and yellow-to-red emission color change due to deprotonation, in which DPP3 exhibits the best sensitive property and detects fluoride concentrations in a range of 0-10μM at visible region wavelengths.In charpter 3, in order to modulate the ICT process of DPP molecule, a new red-emission diketopyrrolopyrrole (DPP)-based fluoride ion chemosensor (DPP4) with two strong electron-donating triphenylamine groups was designed and synthesized. The sensing properties of DPP4 for F-were extensively investigated in dichloromethane (DCM), acetone and acetonitrile solutions. Deprotonation of the N-H groups on DPP4 provided rapid and selective detection of F-, in which an apparent color change from red to purple with large red shift in ambient light can be observed by the naked-eye indicating a similar ratiometric way in all three solvents. However, very distinct sensing behaviours were obtained in the fluorescent changes exhibiting solvent-dependent ternary mode approaches, i.e. "turn off", ratiometric and "turn on" modes in DCM, acetone and acetonitrile, respectively. In DCM, a "turn off" response with 27 nm red shift from 608 nm to 635 nm can be found upon addition of n-Bu4NF. In acetone, ratiometric channel was activated and 51 nm red shift from 590 nm to 641 nm was obtained and accompanied with emission color from orange to purple red. In acetonitrile, a "turn on" response with red emission at 631 nm can be easily recognized, and more than 50-fold enhancement were obtained. Interestingly, using fluoride and HSO4- anions as two chemical inputs and absorption or fluorescence as output, compound DPP4 is demonstrated to be a parallel double-INH logic gate in acetonitrile solutions.In charpter 4, a new DPP-based conjugated polymer PDPP1 was designed and synthesized through Suzuki couple reaction. Upon addition of 2μM fluoride ion, noticeable quenching response can be detected in THF solution of PDPP1. The formation of a small number of local band gap traps upon deprotonation reaction with fluoride ion provided an ultraquenching fluorescence sensory methodology. The peak at 570 nm was absolutely disappeared with 200μM fluoride ion, and a new emission band centered at 656 nm was emerged, which assigned to the deprotonated derivatives. In absorption spectra, the band of PDPP1 centered at 516 nm was decreased and the deprotonated peak emerged at 625 nm while the solution colour changed from red to purple.In chapter 5, two new thiocarbonyl quinacridone compounds (TQA1 and TQA2) were designed and synthesized, and their sensing properties were investigated. The measurements of sensing behavior to various metal ions reveal that both of them are excellent "turn on" fluorescent chemosensors for mercury ion. Addition of Hg2+ to the chloroform solution of TQA2 gave the lowest detection limit at 4.7 nM. In addition, colorimetric changes from green to red of sensors interacted with Hg2+ are also successfully demonstrated. The recognition is attributed to Hg2+-induced conversion of green thiocarbonyl quinacridones into their red carbonyl analogues.In chapter 6, based on small molecular quinacridone analogues, five conjugated polymers PTQA1～PTQA5 were synthesized with different sulphidation conversion rate. PTQA1～PTQA5 were characterized by H NMR and IR spectra. Fluorescence quenching process is determined by the sulphidation conversion rate of carbonyl groups in quinacridone. The absorption titration experiment of PTQA3 proved the conversion process among dithioquinacridone, monothioquinacridone and quinacridone with color changes from green through purple to red. Furthermore, the fluorescence intensity at 566 nm showed an approximate 40-fold emission enhancement after addition of Hg2+ ion.In chapter 7, triphenylamine-based two-photon fluorescent sensor TPAl was designed as an activated Michael acceptor type of chemodosimeter for cyanide in 100% water. Two pyridine groups were attached to triphenylamine moiety through Suzuki reaction to improve the water solubility. Cyanide ion can attack theα-site of vinylidene cyanide, leading to decrease ICT process of TPA1 and give dramatic changes in both absorption and fluorescence spectra. Under two-photon excitation at 800 nm, TPA1 also showed quenching response with addition of 0～14μM cyanide ion. And the two photon absorption (2PA) cross sections were determined to be 24 GM and 134 GM in water and DCM solutions, respectively. Laser Scanning Confocal Microscope (LSCM) was employed to track cyanide ion in Hela cells with this chemodosimeter.In chapter 8, a new hyperbranched polyyne (PTEPA2) with polytris(4-ethynylphenyl)amine as the core, benzoyl thioureanaphthalimide as Hg2+ detected unit was designed and synthesized. The addition of Hg2+ transforms the thiourea unit of the chemodosimeter under THF conditions into an imidazoline moiety that is a much less electron-donating group, and hence results in a reduction in electron delocalization within the fluorophore. The emission maximum exhibits blue-shift and increase of fluorescent intensity. To confirm selectivity of the sensor towards mercury ions, it was also titrated with other divalent metal ions. No significant change was observed in the fluorescence spectra.