| The aggregation-induced emission(AIE)phenomenon refers to a phenomenon in which organic molecular compounds do not emit light in solution but emit bright light in an aggregated state or solid state.Because the unique luminescence properties of aggregation-induced emission organic materials can effectively overcome the aggregation-induced quenching phenomenon(ACQ)of traditional organic fluorescent dyes,Therefore,they have good application prospects in many fields such as microenvironment monitoring and cell imaging.With the deepening of its research,the current development of aggregation-induced luminescent organic materials has made great progress,and the full-spectrum emission from visible to near infrared can be achieved through the structural design of the aggregation-induced emission(AIE)molecule.However,there are still some problems in current research.Most of the aggregation-induced emission organic molecules are only short-lived fluorescent molecules,so their applications in biological systems and other fields have been largely limited.At the same time,due to the limitation of the spin-forbidden law,the design of organic room-temperature phosphorescent materials also has great difficulties and challenges.In this context,combining the aggregation-induced emission and the organic room-temperature phosphorescence to achievelong-lived efficient room-temperature organic phosphorescence,and the development of aggregation-induced organic phosphorescence materials with long lifetimes will bring huge benefits to the field of luminescent organic materials.In this thesis we designed and synthesized a series of significant aggregation-induced emission organic materials using tetrafluoroterephthalonitrile and tetrachloroisophthalonitrilebased on the design rules of electron acceptor-donor modular organic phosphorescent materials.It was found that the change of the substituent position will greatly affect the luminous behavior of the substance,and it was also found that when 2,4,5,6-tetra(3-hydroxyphenylthio)-isophthalonitrile was irradiated with ultraviolet light,the molecule undergoes obvious photochromic phenomena.The following are the main contents of this study:(1)Compared with traditional organic fluorescent dyes,luminescent agents(AIEgens)with aggregation-induced emission(AIE)properties can emit bright light in the aggregated state or solid state,so they can fundamentally effectively compensates for the defect of aggregation-induced quenching(ACQ)of traditional organic fluorescent dyes.But so far,the research on the properties of aggregation-induced emission(AIE)has mainly focused on aggregation-induced fluorescence with a short lifetime.The research and application of aggregation-induced phosphorescence(AIP)is still scarce,and only a few.research and applications involved in aggregation induced phosphorescence(AIP)have been reported.In this chapter,we designed and synthesized a group with significantly different photophysical properties through the substitution reaction of 2,3,5,6-tetrafluorobenzene-1,4-dinitrile(TFBD)with three isomeric mercaptophenols.The introduction of three isomers of mercaptophenol surprisingly produced three luminescent molecules with aggregation-induced phosphorescence,aggregation-induced enhanced phosphorescence,and dual-state fluorescence.The results show that 2,3,4,5-tetrakis(3-hydroxyphenylthio)-benzene-1,4-dinitrile(m-THPT)and 2,3,4,5-tetrakis(4-hydroxybenzene)thio)-benzene-1,4-dinitrile(p-THPT)are typical aggregation-induced phosphorescent molecules,while benzo[5,6] oxathieno[3,2-b]benzothiazine-6,13-dicarbonitrile(BOPDC)is a typical dual-state emission molecule.Through theoretical calculations we found that the HOMO orbitals of 2,3,4,5-tetrakis(4-hydroxyphenylthio)-benzene-1,4-dinitrile(p-THPT)and2,3,4,5-tetrakis(3-hydroxy phenylthio)-benzene-1,4-dinitrile(m-THPT)are mainly located on two hydroxyphenyl units adjacent to the cyano groups,and their LUMO orbitals are contributed by the central phenyl unit.Such a structure promotes intersystem crossing process,which results in phosphorescence.The HOMO orbital of benzo[5,6] oxathieno [3,2-b]benzothia-6,13-dicarbonitrile(BOPDC)is composed of a central paraphthalonitrile and two adjacent mercaptophenol group contributes evenly,while its LUMO orbital is mainlycontributed by the atomic orbital constituent unit of phthalonitrile in the center.As a result,it does not participate in the transition process between systems,and then generates fluorescence.(2)Because most molecular switches need to be between two or more stable states to realize their functions,and they also need to continuously provide energy to work properly,there are many inconveniences in practical applications,and they also make them reduced repeat time.At the same time,traditional molecular switches often exhibit aggregation-induced quenching(ACQ)at high concentrations,which limits better development.Luminogens with aggregation-induced emission(AIE)can be used in the aggregated state or solid state,which effectively compensates for the defects induced by aggregation-induced quenching(ACQ).Based on this property,We used2,4,5,6-chloro-1,3-phthalonitrile(TBDB)and 3-hydroxythiophenol as raw materials to synthesize 2,4,5,6-tetrakis(3-hydroxyphenylthio))-isophthalonitrile(THPI),it was observed that the solid state of 2,4,5,6-tetrakis(3-hydroxyphenylthio)-isophthalonitrile(THPI)at room temperature emits a bright light with obvious aggregation-induced emission(AIE)properties.Through further observation,we found that when its tetrahydrofuran solution was irradiated with a 365 nm ultraviolet lamp,the solution emits orange-red light,but after a period of time,the orange-red light disappeared and the solution emited cyan.It can be verified by other characterization methods that the chemical structure of the molecule has not changed before and after the illumination,and it can be restored to its original state under certain conditions. |
