Synthesis And Properties Of Polythiophene Derivatives Containing Diamino Moieties In The Side Chain

Polythiophene derivatives were widely studied and applied for their good electro-optical properties and chemical stability. The design of new type of water-soluble polythiophene derivatives and research on their application as chemo-sensor and biosensor has a vital theoretical and practical significance.In this paper, poly{3-[(4-{[2-(dimethylamino)ethyl]amino}cyclohexylidene)methyl]-thiophene}(PTDA1), poly{3-[(4-{[3-(dimethylamino)propyl]amino}cyclohexylidene) methyl]thiophene}(PTDA2) and poly{3-{[4-(4-methylpiperazin-1-yl)cyclohexylidene] methyl}thiophene}(PTDA3) were synthesized from diethyl(thiophen-3-ylmethyl) phosphonate via several steps of Wittig-Horner reaction, hydrolysis, reductive amination and FeCl3 oxidative polymerization reaction. Based on this, poly{3-({4-[(2-hydrazino-2-oxoethyl)(methyl)amino]cyclohexylidene}methyl)thiophene}(PTHA1) and poly{3-({4-[(3-hydrazino-3-oxopropyl)(methyl)amino]cyclohexylidene}methyl)thiophene}(PTHA2) were synthesized from 4-(thiophen-3-ylmethylidene)cyclohexanone through reduction ammoniation, substitution or Michael addition, hydrazinolysis and FeCl3 oxidative polymerization reaction. In addition, poly{3-[2-(2-dimethylamino-ethylamino)ethoxy]-4-methyl-thiophene}(PTMA) was obtained from 3-bromo-4-methylthiophene via substitution, alcoholysis, amino substitution and FeCl3 oxidative polymerization reaction. The above six kinds of polythiophenes and reaction intermediates were characterized by nuclear magnetic resonance hydrogen spectrum(1H NMR), Fourier transform infrared spectroscopy(FTIR), mass spectrometry(MS), gel permeation chromatography(GPC). Also, their optical properties and applications were studied and analyzed through UV-vis spectroscopy and fluorescence emission spectrum. As these polymers have flexible side chains with polarity functional groups, they are soluble in methanol, chloroform, tetrahydrofuran, acetonitrile and other common solvents.The polythiophene derivatives with double aminos in their side chains exhibited excellent optical properties, and they were applied for the detection of heavy metal ions and amino acids, which is very important. Research on the reported water-soluble polythiophene poly[N,N,N-trimethyl-4-(thiophen-3-ylmethylene)cyclohexanaminium chloride](PTCA-Cl), poly[3-(1,1’-dimethyl-4-piperidinemethylene)thiophene-2,5-diyl chloride](PDPMT-Cl), poly{3-[1-(2-trimethylammonium acetyl)piperidine-4-methylene]thiophene-2,5-diyl chloride}(PTAPT-Cl) and poly{3-[1-(2-trimethylammonium butyryl)piperidine-4-methylene] thiophene-2,5-diyl chloride}(PTBPT-Cl) showed that these four polymers could selectively detect Hg2+ in methanol/water solution by fluorescence and colorimetric method, and showed good sensitivity(detection limit reached 10-9 M). PTDA1, PTDA2 and PTDA3 exhibited selective detection of Hg2+ in methanol/water(1:1) system, and PTDA1 showed well selectivity toward Cu2+ in THF/water(1:1) system. We found that the recognition of Hg2+ and Cu2+ in different aqueous solutions was based on electrostatic interactions and complexation, respectively. In addition, we found that the Cu2+ quenched fluorescence could be recovered with the help of amino acids. Thus, the resulting PTDA1-Cu2+ system could be used as a sensing platform for detecting amino acids.For PTHA1 and PTHA2, subtle structural differences of their side chains resulted in their different optical properties. PTHA1 could recognize Cu2+ with high sensitivity in buffer solution containing tetrahydrofuran(detection limit reached 10-10 M), accompanied with visible fluorescence quenching phenomenon. While PTHA2 showed no significant fluorescence responses to any metal ions. Further more, PTMA with tridentate N/O ligand on its side chain could recognize Co2+, Cu2+ and Cd2+ in buffer solution containing acetonitrile. The presence of Co2+ and Cu2+ could lead to fluorescence quenching of PTMA, along with a color change of the solution from yellow-green to colorless. An obvious red shift of UV-vis absorption could be observed in the presence of Cd2+, accompanied with color change of the PTMA solution from yellow to pink. At the same time, the fluorescence of PTMA could be selectively quenched by Cu2+ in tetrahydrofuran buffer solution, with detection limit of 10-9 M. The quenched PTMA-Cu2+ system could be used as fluorescence “turn-on” probe for detecting homocysteine and glutathione.