Preparation And Performance Of Nitrogen-containing Porous Conjugated Polymers

Surface-enhanced Raman scattering（SERS）,as a high-sensitivity,non-destructive and rapid analysis technique,has broad applications in the fields of surface science,spectroscopy,chemical analysis and biological detection.The electromagnetic enhancement（noble metal nanostructures）and chemical enhancement effects（semiconductors）of the material enhance the Raman signals of probe molecules on the substrate.However,noble metal substrates still have many deficiencies and defects in chemical stability,"hot spot"construction,sensitivity under long-wavelength laser excitation,and recovery and recycling.Exploring new non-metallic substrates has always been one of the most important research directions in SERS technology.Semiconductors with the special physical and chemical properties can overcome many defects of noble metal substrates.The structure and properties of organic/polymer semiconductors can be easily chemically modified,which provides a possibility to obtain semiconductor SERS substrates with a high activity and high sensitivity.Conjugated porous polymers（CPPs）are a class of amorphous or crystalline polymer semiconductors linked by covalent bonds,with large specific surface area,good chemical,light and thermal stability,and the turnable energy bands controlled by designing aromatic monomers.The energy bands of CPPs can be adjusted by choosing appropriate conjugated structures via chemical modification to make charge transfer occur between CPPs and probe molecules.And then,the amplificating Raman signal of the probe molecules is realized based on chemical enhancement mechanism.In this paper,a series of nitrogen-containing CPPs have been synthesized and explored possiblity as SERS substrates and their SERS mechanism.In order to achieve this objective,the research work mainly contains the following aspects in this thesis:In the second chapter,the CPPs,PCMP-1 and PCMP-2,with pyridine cores have been synthesized in an autoclave based on the Chichibabin reaction.The structures and properties of PCMP-1 and PCMP-2 have been investigated by Fourier transform infrared（FT-IR）spectroscopy,X-ray diffraction（XRD）,scanning electron microscope（SEM）,Ultraviolet-visible（UV-vis）,and photoluminesence（PL）spectroscopy.The experimntal results indicate that the crystallinity and conjugation scale of polymers can be tuned by adjusting the reaction time,reaction method,and monomer structure.The Brunauer-Emmett-Teller（BET）surface areas of PCMP-1 and PCMP-2 have been tested by a nitrogen adsorption-desorption analysis test.The effect of metal ions on the fluorescence of PCMP-1 has been preliminarily explored and found that Fe³⁺had obvious fluorescence quenching effect.The iodine vapor can be adsorbed by PCMP-1,and its maximum adsorption capacity is 0.51 g/g.However,PCMP-1 and PCMP-2 cannot be used as Raman substrates due to their good fluorescence properties.In the third chapter,covalent triazine frameworks,CTF-Cz-1 and CTF-Cz-2,have been obtained by nitrile trimerization catalyzed with superacid.The structure and morphology of the polymers have been characterized by means of FT-IR,XRD and SEM.Due to the photoinduced electron transfer effect,the PL intensity of CTF-Cz-2 is decreased significantly,and the SERS spectrum of rhodamine 6G（R6G）absorbed on CTF-Cz-2 is obtained.The SERS mechanism of CTF-Cz-2 was preliminarily explored by analyszing the energy bands,PL spectra and time-resolved PL spectra of CTF-Cz-2 and R6G.In the fourth chapter,triazine-based conjugated porous polycarbazole（PCz-1）has been synthesized via Friedel-Crafts alkylation reaction.The structure and morphology of PCz-1 were characterized by FT-IR,XRD,SEM and other means.The BET surface area of PCz-1 is confirmed to be 80.52 m²/g by nitrogen adsorption and desorption analysis.The SERS ability of PCz-1 is optimized by adjusting catalyst dosage,reaction time and temperature.The experimental results show that PCz-1 with excellent SERS effect can be obtained by choosing the reaction condition of 1 m L of methanesulfonic acid for 12 h at 140°C.Using R6G as the probe molecule,the SERS enhancement factor is as high as 6.81×10⁵,and the detection limit is10^-7 M.The SERS mechanism of PCz-1 is fundamentally established by analyzing the SERS spectra of a series of probe molecules,the PL and time-resolved PL spectra.In chapter 5,a series of PCzs have been synthesized from indolocarbazole,bicarbazole and carbazole monomers with different alkyl-substituted carbazoles via Friedel-Crafts alkylation according to the optimized reaction conditions in the previous chapter.The structure and morphology of the polymer materials are characterized by means of FT-IR,NMR,XRD and SEM technologies.Spectral analysis and cyclic voltammetry test results indicate that the energy band of PCzs can be changed by 9-position substituent and conjugation of carbazole monomer.The polar groups in PCzs can improve their ability to adsorbing probe molecules.The SERS spectra of R6G are obtained by using PCzs as the SERS substrates.The SERS mechanism of PCzs is further verified and clarified by analyzing the relationship between the SERS intensity and energy bands,PL and time-resolved PL spectra.