Preparation And Properties Of Amide-based Nonconventional Room Temperature Phosphorescence Materials

Pure organic room temperature phosphorescence(RTP)materials are receiving more and more attention due to their unique photophysical properties and wide applications,such as organic light-emitting diodes(OLED),chemical/biological probes,and biological imaging.Traditional pure organic luminescent materials usually contain a large number of conjugated units,such as benzene rings.However,these materials have some inherent shortcomings:firstly,conjugate extension is accompanied by more structural complexity usually,making some?-extended chromophores difficult to synthesize and expensive;secondly,the synthetic processes will generate a lot of waste,which harmful to the environment;finally,the benzene ring is toxic to human and is difficult to degrade in the natural environment.Therefore,nonconventional luminescent materials with RTP characteristics that do not contain aromatic groups have received sustained attention from researchers attributed to their environmental friendliness,easy preparation,and low cost,however,the researches on nonconventional luminescent materials are still in its infancy,and it is of great significance to further explore their luminescent mechanism and expand their types and applications.Polymerization engineering is an effective strategy to realize RTP of nonconventional luminescent materials.Photoluminescent polymers without aromatic groups obtained from nature or by polymerization are collectively known as nonconventional luminescent polymers(NLPs).This paper mainly studies on the luminescent mechanism of NLPs through theoretical calculations based on small molecules with simple structure as a model,then to guide related experiments;On this basis,the subject conducts experimental research on the photophysical properties and moisture resistance of amide NLPs with RTP characteristics,proposes strategies to realize and enhance phosphorescence emission of amide NLPs,and explores their applications in the field of time-resolved information encryption,which providing certain design ideas for people to build nonconventional luminescent materials with RTP characteristics and excellent moisture resistance.The main research contents and results of this paper are as follows:(1)Using acetamide and acetic acid as models,calculating the spin-orbit coupling(SOC)constants and energy gap(E_g)of acetamide-acetamide,acetic acid-acetic acid and acetic acid-acetamide,respectively.And calculating the hydrogen bond strength of acetamide-H₂O,acetic acid-H₂O,acetamide-acetamide,acetic acid-acetic acid,and acetic acid-acetamide;studying the photophysical properties of acetamide,acetic acid and acetic acid-acetamide under ambiance and 77 K;thereby analyzing the mechanism of luminescence of amide NLPs and proposing the methods to improve the moisture resistance of amide NLPs.The results show that strong hydrogen bonding can be formed between acetamide and acetic acid,and their intermolecular strong hydrogen bonds can inhibit non-radiative transitions,thereby promoting phosphorescence emission.(2)Three kinds of NLPs with RTP characteristics were prepared—polyacrylamide(PAM),polyacrylic acid(PAA)and blends of polyacrylamide-polyacrylic acid(PAM-PAA)basing the above results of theoretical calculation,and proposing strategies to realize and enhance phosphorescence emission of amide NLPs.The structures of PAM,PAA,and PAM-PAA were determined through structural characterization;Then studying their photophysical properties and moisture resistance at room temperature,the results showed that the RTP lifetime of PAM-PAA was the longest,reaching 20.87 ms;at the same time,the moisture resistance of PAM-PAA is the best among the three samples,which further verifies the results of the theoretical calculation—the hydrogen bonds played the key role for them.(3)The above results indicate that the RTP emission of the polymer can be enhanced by blending.However,there is phase separation between the blended components.In order to achieve molecular-level interaction and further enhance the hydrogen bond strength,the experiment has constructed four kinds of amide-based NLPs with RTP characteristics—P1,P2,P3 and P4 through free radical copolymerization.The structures of P1,P2,P3,and P4 were determined through structural characterization;then studying their photophysical properties and moisture resistance at room temperature,the results showed that they all had obvious RTP,and the RTP performance of P1 was the best,with phosphorescence lifetime of 0.83 ms and phosphorescence efficiency of 12.00%;at the same time,P1 showed excellent moisture resistance;the above provided an effective strategy for people to obtain nonconventional luminescent materials with RTP characteristics,good moisture resistance and time-resolved information encryption applications.In addition,in order to further enhance the RTP performance of NLPs,ionic bonds are introduced on the basis of P1 to further improve the intermolecular/intramolecular interaction,and chemical modification for P1 was used by adjusting the amount of alkali(Na OH),and three new amide NLPs with RTP characteristics—P1-M,P1-Y and P1-D were obtained.It shows that their RTP lifetimes were all over 100 ms,and P1-Y is the longest,reaching 134.66 ms;this chemical modification is convenient and efficient,and provides an effective strategy for people to obtain nonconventional luminescent materials with ultra-long RTP.(4)In order to further verify the feasibility of the RTP strategy for nonconventional luminescent materials provided in this article,on the basis of the amide group,a hydroxyl group that easily forms a hydrogen bond was introduced,and five new amide NLPs with RTP characteristics were constructed through the free radical copolymerization—P₁,P₂,P₃,P₄ and P₅ to further verify the feasibility of the RTP strategy for realizing nonconventional luminescent materials provided in this paper.The structures of P₁,P₂,P₃,P₄ and P₅ were determined through structural characterization;then studying their photophysical properties at room temperature,the results showed that they all have obvious RTP,and P₅ had the best phosphorescence performance;these showed that the achieving RTP strategy of nonconventional luminescent materials in the previous article is exact,efficient and convenient.The experimental results are of great significance for further understanding the luminescence mechanism of nonconventional luminescent materials and expanding their types.