| Recently,stimuli-responsive optical materials have attracted great attention for their potential applications in the displays,sensors and memories.Compared with the triggers such as light,temperature,pH and magnetic field,the electrical stimuli is more advantageous because it could be applied rapidly,environmental,locally,reversibly and remotely.So far,electrochromic and electrofluorescent materials are the mostly studied electro-responsive materials.Electrochromism have been studied thoroughly,and various electrochromic materials and their mechanism have been reported.Moreover,electrochromic smart window and energy-saving displays have been commercialized recently.By contrast,electrofluorescent materials are still in the laboratory stage due to their poor performance,which stimulate the development of high-performance materials with high stability and sensitivity.Fabrication stable electrochemistry/high quantum yield electroactive fluorophore based on electrochromic moieties will be an effective method to realize high-performance electrochromic/electrofluorescent dual-switching properties.For example,electro-rich triarylamine is ideal anodic electroactive unit,and electrochromic materials containing triarylamine possess many advantages including low trigger voltage,colorless normal state and excellent electrochemical stability.Based on molecular design,electrochromic/electrofluorescent dual-switching materials with high switching stability,high contrast and good processing properties could be obtained by the synthesis of high performance polymers with arylamine-fluorophores.In this paper,we designed and synthesized several series of electroactive and fluorescent polyamides/polyimides.We studied the relationship between the structures and properties through analyzing electro-switching properties affected by the structures of electroactive fluorephores,different linkage of polymers and copolymerization,which will greatly promote the development of bifunctional materials with high performance properties and easily processing properties.Our research work mainly included four parts listed as followed:First,we designed a novel electroactive fluorophore: dimethlyfluorene-diphenylamine,and we synthesized diamine and diacide containing this novel unit,respectively.We successfully prepared two series of polyimides(MeFPI)and polyamides(MeFPA)from the new diamine with commercial dianhydrides and diacides.The resulting polymers exhibited good electrochemical stability as the fluorene-diphenylamine could protect the para-position of the triphenylamine effectively.Compared with MeFPI,MeFPA possessed reduced oxidation potential and improved electrochemical stability,which could be attributed to the strong electron-withdrawing amide group in MeFPI backbone.MeFPI exhibited reversible electrochormic property with color changing from light yellow to green,and MeFPA exhibited reversible color changes from nearly colorless to light green.MeFPA exhibited more stable electrochromic switching properties in comparison to MeFPI,and its electroswitching was still revesible even after 500 cycles.Compared with aromatic polymers,semi-aromatic polymers revealed strong fluorescent emission in NMP solutions,which could be explained by the fact that the alicyclic structure effectively reduced the charge-transfer between the diphenylamine donor and amide/imide acceptor.Furthermore,the fluorescence of the semi-aromatic polymers could be modulated by the electrochemisty reversibly with a contrast ratio of 78 and 83;the relatively low contrast was attributed to the large quenching effect of polymer films by the π-π stacking.Additionally,we prepared a novel series of polyamide(MeFPA’)from the new diacide and commercial diamines.Compared with MeFPA,MeFPA’ exhibited much improved fluorescent properties in either solution state or film state due to their extended conjugation and low energy band gap,and thus,the electrofluorescence of MeFPA’ showed a high contrast up to 221.4.In addition,the electrochromic films of MeFPA’ revealed a reversible color changes from nearly colorless to green.However,the electrochemical stability of MeFPA’ was poor,due to the electron-withdrawing carbonyl group bonding to dimethylfluorene-diphenlyamine unit,which also led to the reduced electroswitching stabilities of electrochromic and elecfluorescent process.Second,for the full consideration of electrochemical stability and film quantum yield,we designed and synthesized two kinds of diamines with diphenyl/hexylfuorene-diphenylamine units,and prepared four semi-aromatic polymers from the two new diamines: PhFPA、HeFPA、PhFPI、HeFPI.Introduction of bulky phenyl and hexyl groups into the 9-position of fluorene could effectively prevent the π-π stacking of the polymer chains,and thus improved the contrast ratio of electrofluorescent process.PhFPA and HeFPA exhibited similar electrochromic properties with MeFPA,while PhFPI and HeFPI exhibited similar electrochromci properties with MeFPI,indicating that the introduction of substituent group on the 9-position of fluorene had less effect on the energy level structure of the resulting polymers.Similarly,PA exhibited more stable electrochemical properties with weak decay in the electroswitching process of electrochromism and electrofluorescence,realizing color/fluorescence dual-switching with high contrast and high stability.Third,to prevent the irreversibility of electroactivity by peroxidation and improve the switching stability,we designed and synthesized a new diamine with electron-donating methoxy substituted bisarylamine-fluorene unit,and prepared the corresponding polyamide(BFPA).BFPA exhibited two reversible redox couples with low oxidation potentials.The BFPA film showed excellent reversible stability of multicolor electrochromic characteristics(colorless-red-blue)after over 1000 cyclic switches.Semi-aromatic BFPA exhibited strong fluorescence with quantum yield up to 50.2% in NMP solution,and the fluorescence could be reversibly modulated by electrochemical redox with superior stability in continuous 100 cycles.In addition,we prepared a novel copolyamide(MFCOPA)from the new diamine mentioned above and “4,4-diamine-4-methoxyltriphenylamine”.Based on color mixture law,the MFCOPA exhibited “nearly colorless-red-black-bule” color changes,which achieved “transmittance-to-black” electrochromic process during the applied potential from 0 to 0.8 V.Moreover,the “transmittance-to-black” electrochromic MSCOPA exhibited high contrast and high stability.At last,considering the fluorescence quenching of polymer films with “arylamine-fuorene” units,we designed and synthesized AEE-active semi-aromatic polyamide with methylsulfonytriphenylamine(SPA).SPA exhibited AEE fluorescence with film-state fluorescent quantum yield up to 32.1%.In addition,we also prepared a novel copolyamide with the “4,4-diamine-4-methoxyltriphenylamine” as the copolymerization diamine(MSCOPA).MSCOPA also exhibited AEE fluorescence with film-state fluorescent quantum yield up to 22.8%.SPA showed reversible color changes from nearly colorless to purple,and MSCOPA showed multiple color changes(nearly colorless-bluish green-bluish purple).MSCOPA exhibited highly stable electrochromic switching over hundreds of cycles during the first redox process,which is similar to the polyamide MPA.Remarkably,the fluorescence of MSCOPA quenched upon the application potential from 0 V to 0.8 V with a high contrast,and the electrofluorescence process was very stable without obvious decay in 100 continuous cycles.Thus,MSCOPA could act as a high-performance electrochromic/electrofluorescent dual-switching material with high stability,high contrast and facile processability. |
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