Synthesis And Properties Of Heterocyclohexylidenemethyl Substituted Polythiophene Derivatives

In recent years, the polythiophene derivatives have desirable electrochemical activities,good environment stability, easy processibility and so on. Therefore, they have attached greatattention in photovotatic cells, light-emitting diodes, fieid-effect transistors and so on. Theystill need to improve their photoelectric properties for practical applications.In this paper, we used3-thienylmethanol as starting materials, undergoing bromination,esterification, Witting-Horner reaction, deprotection reaction. We abtained four monomerscontaining3-(cyclohexylidenemethyl)thiophene,4-(thiophen-3-ylmethlidene)tetrahydro-2H-pyron,4-(thiophen-3-ylmethlidene)tetrahydro-2H-thiopyron,4-(thiophen-3-ylmethlidene)piper-idine. The polymers were synthesized by chemical polymerization using FeCl3as the oxidizingagent at0℃. The structure of polymers and monomers were characterized by1H NMR and IR.Molecular weight of polymers was performed with gel permeation chromatography (GPC). Westudied basic properties of the polymers, the results exhibit that they have good solubility,good film-forming ability and good thermal stability. The UV-vis spectra of these polymersdemonstrated that absorption wavelength of the polymers were dependent on polarity andsteric hindrance of the side chains. Interestingly, maximum absorption of the polymers did notexhibit any significant red or blue shift from solution to film except thatpoly(3-(4-pyranylidenemethyl)thiophene) films are red shifted by32nm. The effects ofvarious solvents in changing the conformation of main chains of these polymers are alsostudied by means of UV-vis absorption spectroscopy. All these polythiophene derivativesshow strong photoluminescence in a region of500-600nm. The results indicate that theemission color of the polythiophene derivatives can be tuned from orange to green bychanging heterocyclohexylidenemethyl group of the side chains. Meanwhile, the energy gapsof these polymers were calculated from the optical measurements(about2.0eV). We alsostudied the electrochemical properties of the polymers and calculated the polymer HOMOlevel. Finally, the morphologies of the films were homogeneous with micro/nanostructures.Meanwhile, poly(3-(4-piperidylidenemethyl)thiophene) modifying derivatives,poly(3-(1-benzyl-4-piperidylidenemethyl)thiophene), poly(3-(1-phenylcarbony-4-piperidylidenemethyl)thiophene), poly(3-(1-mesyl-4-piperidylidenemethyl)thiophene), poly(3-(1-((4-Met hylphenyl)sulfonyl)-4-piperidylidenemethyl)thiophene), Poly(3-(1-octyl-4-piperidylideneme-thyl)thiophene), Poly(3-(1-decyl-4-piperidylidenemethyl)thiophene), Poly(3-(1-octanoyl-4-pi-peridylidenemethyl)thiophene) and Poly(3-(1-decanoyl-4-piperidylidenemethyl)thiophene)were also synthesized and characterized to further study the influences of different moieties ofthe4-piperdylidenemethyl side-chain on the properties of the polymers. The structures of thepolymers were characterized by1H NMR and IR. We also studied the molecular weight byGPC and thermal stability by TGA. The results indicate that the polymers have good goodthermal stability and low molecular weight which was due to steric hindrance of the sidechains. The absorption spectra of all polymers are in the scope of the visible light. Furthermore, the absorption spectra studied the effects of side chains with different lengths anddifferent end groups in changing the conformation of the polymer main chains. The results ofphotoluminescence indicate that the emission color of the polythiophene derivatives is yellow.The optical bandgap energy of the polymers is about2.0eV, which is advantageous inapplication of photoelectrical materials. The electrochemical properties of the polymers aredetermined by three-electrode system and calculate the polymer HOMO level. TheSEM images of polymer films show that the films are composed of micro/nano-sphericalparticles.