Synthesis and Properties of Dual-state Light-emitting Polythiophene Electrochromic Materials

Author:Wu Jing Chuan

Supervisor:xu chun ye


Degree Year:2019





Electrochromism(EC)refers to the phenomena that the optical properties(transmittance and absorption)of the materials undergo a stable and reversible change under an external electric field.This optical phenomena are mainly caused by the oxidation-reduction reactions of the materials themselves,and the doping and de-doping processes with charged ions,resulting in macroscopic changes in absorbance and color.Because of this unique optical changes,electrochromic materials have been widely used in various fields,such as glare-proof mirrors,sunglasses,and e-books.At the same time,due to its short material synthetic cycle,easy preparation,rich color expression,high optical contrast and fast response time,it has attracted the much attention and research by many researchers.Among the different kinds of electrochromic materials,polythiophene shows great commercial application prospects owing to it has simple chemical structure,many kinds of derivatives,high stability to air and humidity,rich color and the ability of tuning easily its electrochromic properties.This dissertation mainly focuses on the research of polythiophene electrochromic materials.By changing its chemical structure and introducing functional groups,a series of polythiophene electrochromic materials with different colors and functions have been synthesized.The research work mainly concentrates on the optimization of color,solubility and electrofluochromic property of polythiophene electrochromic materials,including the following three portions:In the first part of our work,we mainly have prepared a new type of soluble green to transmissive polythiophene electrochromic material.Compared with the traditional green electrochromic material,the material contains the novel donor-acceptor-donor conjugated main chain structure,which could help to reduce the polymer energy gap and the external applied voltage.The redox voltage of polymer are 0.60 V and 0.25 V,respectively.The color of polymer can switch from green to transparent with a high optical contrast of 53%,occurring at 650 nm,and the electrochemical response time is fast with reduction process of 1.19 s and oxidation process of 1.16 s.In addition,we introduced a dodecyloxy long chain on the side chain of the polymer to improve the solubility of the polymer,so that it can be dissolved in common organic solvents with lower boiling points such as propylene carbonate,acetonitrile and dimethyl sulfoxide.In order to change the method of polymer film prepared by the conventional electropolymerization,a more environmentally friendly spray coating method is used to realize the preparation of the polymer film.The device via using the polymer material can achieve green to transmissive with a driving voltage of±1.5 V and a maximum transmittance difference of 28.5%at a wavelength of 658 nm,and the reduction time and oxidation time are 2.0 s and 2.5 s,respectively.The lower redox voltage and the fast electrochemical response time of the green polymer film make it suitable for large-scale application in the field of electrochromic display.In the second part of our work,we have introduced the intermolecular force C—H…π bond into the polythiophene conjugated backbone,and successfully synthesized two novel electrochromic and electrofluorochromic bifunctional polymers P1(containing trans-stilbene)and P2(containing fumaronitrile).These two new polymers maintain excellent thermal stability at high temperatures,with thermal decomposition temperatures of polymers are 369℃ for P1 and 373℃ for P2,respectively.They also have good solubility in common organic solvents,and could emit strong fluorescence in solution and solid states.The polymer films P1 and P2 can achieve an electrochromic process at an applied voltage within ± 1 V,from yellow-green to sky blue and red to rufous,respectively.In synchronization with electrochromic processes,the sprayed polymer films can switch to non-fluorescent state from fluorescent state repeatedly.Besides,as manifested by the optimized dimers geometries of P1 and P2,intermolecular non-covalent C—H…π bonds existing in neighboring polymer backbones,restrict the intramolecular rotations and then attain fluorescence both in film and solution states.This unique property makes the polymers special candidates for optoelectronic applications.In the third part of the work,a series of π-conjugated polymers P1-P4 bearing 3,3-bis((2-ethylhexyloxy)methyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine and phenothiazine derivatives were synthesized via direct(hetero)arylation polymerization,exhibiting brown or yellow in their neutral states and green,gray or sky blue in their oxidized states,respectively.This four kinds of polymers exhibit excellent solubility in low-boiling solvents and can be spray coating to prepare films for rapid process.At the same time,the conjugated polymers P1-P4 are capable of maintaining excellent thermal stability at high temperatures,and the thermal decomposition temperatures are 365℃for P1,368℃ for P2,368℃ for P3 and 367℃ for P4,respectively.In the electrochromic process,all four types of polymer films exhibit lower redox voltages and faster electrochemical switching times.Compared with P1 affected by aggregation caused quenching effect,P2-P4 could all display strong green emission both in film and solution.This unique fluorescence phenomenon is derived from the different distance of π-π stacking of the polymer backbone.From P1 to P4,the distance of π-π stacking is increasing,which makes the polymers P2-P4 could restrict the aggregation caused quenching effect of π-π stacking and then emit bright green emission in dual states.In synchronization with electrochromic processes,the sprayed polymer films can switch to non-fluorescent state from fluorescent state repeatedly.These novel copolymers might be special candidates for electrofluorochromic and optoelectronic applications.