Synthesis And Properties Of Fluorescent Polyamic Acid Based On Oligoanilines

As a classic conducting polymer,polyaniline has recently been the center of great attention due to its high conductivity,good stability and wide application.However,the practical applications of polyaniline are hindered by its low solubility,poor processability and mechanical brittleness,attributed to its high rigid molecular structure,and numerous hydrogen bonds.In this regard,it is of great interest to exploit and prepare novel polyaniline-type polymers with enhanced solubility and processability.As the model compounds of polyaniline,oligoanilines have gained much exposure because of their well-defined molecular structure,good solubility and exciting photoelectron performance.Undoubtedly,incorporating oligoanilines into the polymer architecture would be a feasible tactic to improve the processability and flexibility.Meanwhile,the oligoaniline units would maintain its pristine electrochemistry and photoelectron characteristics.Recently,large amounts of novel polymers bearing oligoaniline segments have been designed and fabricated.These resultant polymers exhibit great application potential for anticorrosion,electrochromism,biomedicine and sensors.For further exploration of new architectures,novel features and intelligent applications,more oligoaniline-containing polymers need to be designed and synthesized.Electrofluorochromic materials have gained much exposure in recent years due to their reversible switching of fluorescence intensity upon electrical potentials.The electrofluorochromic property can be generated from the interplay between electroactive unit and fluorescence emission unit.For better understanding of electrofluorochromic mechanism and expansion of practical applicability,electrofluorochromic polymers need to be further explored.Here,we synthesized a series of electrofluorochromic polymers bearing oligoaniline as electroactive units.Firstly,we designed and prepared an electrofluorochromic polyamic acid bearing tetraaniline and fluorene groups through condensation polymerization coupled with postpolymerization functionalization.The tetraaniline served as electroactive unit,while fluorene groups are using as fluorescence emission unit.The fluorescence intensity underwent an obvious decrease with the increase of applied potential,due to the fluorescence quenching effect of quinoid rings from oligoaniline segments.Secondly,a novel electrofluorochromic polymer(POCP)bearing oligoaniline,carbazole and polyhedral oligomeric silsesquioxane(POSS)pendants was designed and synthesized by condensation polymerization coupled with postpolymerization functionalization,which exhibits excellent solubility,and interesting spectroscopic properties.The POSS pendants could improve the electroactivity of POCP due to the rapid electrolyte migration through the polymer film under the potentials,resulting in an enhancement of switching rate in electrofluorochromic performance.Moreover,its fluorescence intensity has also been improved,again due to these huge pendant POSS groups.Finally,we have synthesized a novel electrofluorochromic polyamic acid(POT)bearing oligoaniline and fluorescent triphenylamine segments.The resulting POT revealed a good and reversible electroactivity in a wide potential range of 0.0-1.6 V.An interesting electrofluorochromic behavior was observed,ascribed to the fluorescence quenching effect of quinoid rings and triphenylamine radical cations,respectively.Stimuli-responsive fluorescent materials have gained much exposure in recent years due to their potential applications as sensors,bioimaging,memory media and displays.Chemical substances,temperature,light,pH,electricity and mechanical force are the typical stimuli utilized to change the fluorescent behaviors of these materials.To explore the mechanism of fluorescent switching and impart more functionality,many multiple stimuli-responsive fluorescent materials have been reported.Although great efforts have recently been made to prepare multiple stimuli-responsive fluorescent materials,it still a challenge to reveal the fluorescent switching behavior.Here,we synthesized two multiple stimuli-responsive fluorescent polymers with oligoaniline serving as sensitive units.Firstly,we have demonstrated a successful design and synthesis of multistimuli polyamic acid bearing oligoaniline,triphenylamine and fluorene groups(PAAOTF).The generated fluorescence showed a clear multiple stimuli-responsive behavior against redox species,pH,electricity and pressure,contributed by the sensitive oligoaniline and triphenylamine groups.Significantly,via various triggered stimuli,fluorescence modulation and switching of PAAOTF in both solution and film states was realized easily.The interactions between sensitive units and fluorene groups are responsible for the fluorescent switching behavior.Secondly,we design and synthesize a multifunctional polymer bearing oligoaniline,azobenzene and fluorene units.In this intelligent stimuli-responsive fluorescent system,oligoaniline and azobenzene groups are served as sensitive units,and fluorene groups are responsible for fluorescence emission.The as-synthesized multifunctional polymer displays fascinating multi-stimuli-responsive fluorescence switching performance through structure transition of these sensitive groups upon multiple external stimuli,such as pH value,redox species,potentials and UV/vis light.This delicate molecular design represents an alternative avenue towards a new class of smart,adaptive and responsive polymers.Future work will pay particular attention to molecular architecture design,performance enhancement,and intelligent applications exploration.