Design,synthesis,and Photochemical Reaction Of Twisted A-D-A Structure Organic Luminescent Molecules Based On Triphenylamine

The photochemical reaction has the characteristics of fast reaction speed,simple operation,environmentally-friendly,etc,which was widely used in the fields of drug research and development and natural product total synthesis.And in recent years,the photochemical reaction has also shown good application potential in the field of organic optoelectronic functional materials such as fluorescent switches and fluorescent sensors.Organic luminescent molecules with D-A structure have easy-to-control CT excited state,and exhibit high luminous efficiency and high exciton utilization;at the same time,the CT excited state will also have a greater impact on the photochemical reaction rate,yield and other properties of the D-A molecule,which in turn affects the photoelectric performance and application of the molecule.Therefore,it is of great significance to investigate the photochemical reaction of CT excited luminescent molecules with D-A structure.Triphenylamine is one of the most important donor groups for the construction of D-A molecules with high luminescent properties due to its strong electron-donating ability and three-dimensional spatial structure.By connecting two acceptor groups capable of photochemical reaction to triphenylamine,a class of twisted A-D-A organic molecules with photochemical reaction phenomenon can be obtained.Such molecules not only have a strong CT excited state and excellent photophysical properties,but also may have a more complicated and variable photochemical reaction process,which bring more applications for this type of molecules and their photochemical reactions in the field of organic optoelectronic functional materials.Thus,in this paper,using triphenylamine as the donor group,and the CN-PPV capable of photo-induced E/Z isomerization and the phenylimidazole structure capable of photooxidationand as the acceptor groups to design and synthesize a series of twisted A-D-A structure organic luminescent molecules.And their photophysical properties,photochemical reaction process and possible applications were investigated in depth and meticulously.Chapter 2 designed and synthesized three E/Z isomers Z,Z-TPDCF,Z,E-TPDCF and E,E-TPDCF with twisted A-D-A structure based on triphenylamine（D）and CN-PPV（A）groups.And the specific E/Z isomerization reaction process of organic molecules containing two CN-PPV groups was studied under ultraviolet light through these three isomers.Through the characterization of basic photophysical properties,it was found that all the three isomers showed the obvious CT excited state properties and high AIE activity.And the in situ UV,¹H NMR and HPLC spectra under UV-irradiation clearly showed that both Z,Z-TPDCF and E,E-TPDCF are firstly isomerized into Z,E-TPDCF under UV-irradiation;and the Z,E-TPDCF was almost simultaneously turned into more E,E-TPDCF and less Z,Z-TPDCF due to the calculated lowest unoccupied molecular orbitals of Z,E-TPDCF on the cyanostilbene arm with the Z-configuration.In addition,although all the three isomers in highly polar solvents showed a better configuration stability under UV-irradiation,overall,the configuration stability of Z,E-TPDCF was better than Z,Z-TPDCF and E,E-TPDCF.Chapter 3 designed and synthesized three triphenylamine-imidazole derivative molecules TDBBM,PMTPBM and TPDPM with twisted A-D-A structure based on triphenylamine（D）and phenylimidazole（A）groups,and further investigated the origin of their unusual red-shifted emission in the film state and the photooxidation reaction on the imidazole ring.Comparing with the dilute solutions,the PL spectra of TDBBM,PMTPBM and TPDPM films all exhibited a significantly unusual red-shifted emission peak around 520 nm.Taking TPDBM as an example,a series of studies were carried out on the absorption and emission behaviors of it in the dilute solutions and films under different conditions,and finally confirmed that the aggregation-state red-shifted emission phenomenon actually originated from the photooxidation reaction on the imidazole ring of the molecule,rather than from the formation of excimer in the molecule reported in the literature.In addition,the results of TPDBM’s UV light experiment and in situ UV-vis spectra showed that TPDBM’s photooxidation reaction could generate two products,TPBMZ and TPDYZ,of which TPBMZ was the main product;and the in situ ¹H NMR of TPBMZ indicated that TPBMZ could be further oxidized to TPDYZ.Surprisingly,both the photooxidation products TPBMZ and TPDYZ showed good CT emission characteristics and AIE activity.And finnally,the photochemical reaction of TPDBM doped into PMMA film was suitably applied as a fluorescent probe for oxygen with a lowest detectable oxygen volume ratio of 0.1%.Chapter 4 fixed one A in the molecule as a triphenylimidazole group,and introduced benzothiadiazole and phenylquinazoline groups into the molecule as A’respectively to design and synthesiz two novel triphenylamine-imidazole derivative molecules BMTPBZP and BMTPNKL with twisted A-D-A’structure.And we further investigated their metal ion detection performance to develop a series of excellent Fe³⁺fluorescent probe materials.Response results of the PL and UV-vis spectra of BMTPBZP and BMTPNKL in the presence of different metal ions showed that they could both specifically identify Fe³⁺,and show a blue-shifted enhanced recognition effect.Through a series of experiments,we further studied the recognition mechanism of probe molecules BMTPBZP and BMTPNKL to Fe³⁺,and found that their recognition of Fe³⁺was caused by the electron-rich N atom on the imidazole ring of the acceptor group（A）binding to Fe³⁺in a 1:1 ratio,which caused the molecular CT excited state to recombine and showed a new and stronger CT emission.Similar to BMTPBZP and BMTPNKL,their imidazolyl unit structure PIM and TPA-BM could also specifically recognize Fe³⁺,and have excellent sensitivity and anti-interference.The difference is that the probe molecules PIM and TPA-BM showed a fluorescence quenching recognition effect in the presence of Fe³⁺,in which the fluorescence of TPA-BM was greatly attenuated and a new relatively weak CT emission peak was generated in the red-shifted direction.This result probably because that in the traditional D-A structure TPA-BM molecule,the imidazole unit acts as an acceptor group,but the introduction of the twisted A-D-A’structure change the D-A component in BMTPBZP and BMTPNKL,at this time,the imidazole unit mainly plays a role as a part of the donor group together with triphenylamine.