Study On Synthesis And Fluorescent Property Of Hyperbranched Poly (Amino Ester)s

Nonconjugated AIEgens without phenyl rings possess unconventional chromophores such as aliphatic tertiary amine,carbonyl,ester,and amide.They exhibit high molecular flexibility,biocompatibility and environmental friendliness.They emit strong fluorescent upon aggregate formation,showing typical Aggregation-Induced Emission(AIE)effect,which conquer the Aggregation Cauesed Quenching(ACQ)problem caused by?-?stacking Compared with conjugated AIEgens,unconjugated systems have more advantages in areas of drug loading,gene transfection and cell imaging.However,several drawbacks for nonconjugated AIEgens are still remained,such as complicated synthetic process,low fluorescence intensity,narrow fluorescence range and unclear mechanism.To solve these problems,we have synthesized a novel hyperbranched poly(amino ester)s(HPAE)through one-pot A₂+B₃ polycondensation without any solvent.We carefully studied fluorescent property,latent mechanism of the as-prepared polymers luminescence.Effect of temperature,Fe³⁺and p H on fluorescence properties of HPAE were also investigated in this work.The main research contents of the paper are as follows:(1)A novel hyperbranched poly(amino ester)s containing both ester groups and tertiary amines were synthesized through one-pot A₂+B₃ polycondensation of malic acid(MA)and Triethanolamine(TEA)without any solvent.The structure of M-HPAE were characterized by FTIR,¹H NMR,¹³C NMR and GPC.PL intensity is enhanced as the concentration of M-HPAE rise up or the ethanol fraction goes up in the water-ethanol system,showing typical AIE property.Moreover,the M-HPAE shows excitation-dependent fluorescence.TEM and theoretical calculation studies show that,in concentrated solution,M-HPAE aggregates are formed through hydrogen bonding O-H···O and O-H···N,which results in clustering of ester groups and tertiary amines and the formation of space conjugate.Space conjugate helps the formation of the electron delocalization thus reducing bright blue fluorescence.PL intensity increases when decreasing the temperature of the M-HPAE solution.PL intensity of M-HPAE solution increased with the decreasing of the solvent polarity.In addition,the quenching effect of Fe³⁺on M-HPAE in metal ions is the most obvious,and it is expected to become an ion probe for detecting Fe³⁺in human body.PL intensity of M-HPAE presents a linear response to p H from4 to 10,so the resultant M-HPAE may be a potential candidate as a p H sensor.(2)A novel multicolor water-soluble poly(amino ester)s were synthesized by one-step A2+B3 melt polycondensation using citric acid(CA)and N-methyldiethanolamine(NMDEA).Similar to above fluorescence behavior,the as-prepared polymers have concentration and excitation-dependent behavior.The resulting HPAE exhibits tunable photoluminescence from blue,cyan,green to red irradiated by different wavelength UV light.In addition,the quantum yield of PAE at 40 mg/m L is 0.91%,2.70%,4.48%,1.03%excited at 350 nm,420 nm,470 nm and 550 nm,respectively.Density functional theory(DFT)is used to simulate its assembly structure.The DLS test and TEM result also show that HPAE aqueous solution can form self-assembly of different sizes and morphologies at the same concentration,which form different electronic delocalization and energy gap,resulting different luminescent species with different excitaion wavelength.Moreover,the fluorescence intensity of hyperbranched PAE is much higher than that of linear PAE under the same concentration,so hyperbranched structure plays a key role in light-emitting.The obtained polymers also have potential applications in Fe³⁺ detection.