Design,Synthesis And Optoelectronic Properties Of Organic Luminescent Materials With Spiro [Fluorene-9,2-Imidazole] As The Core

Organic solid-state luminescent materials have been being widely used in organic luminescent semiconductors,biological imaging,and ion detection due to the molecular flexibility,adjustable structure,low cost and wide color gamut.However,although traditional organic fluorophores have good luminescence properties in dilute solutions due to large?-conjugated systems,in the aggregation state,due to their overstrong ?-? stacking and thereafter intermolecular energy transfer,non-radiative energy conversion is caused,and fluorescence is weakened or disappeared totally,which seriously hinders the application of organic luminescent materials.Spirocyclic structures can enhance the rigidity and thermal stability of molecules,and reduce the interactionamong molecules due to the stereoscopic conformations.Previous reports showed that the vertical structure formed by sp3 hybridization of the carbon atoms at the center of the spirocycle could suppress the occurrence of aggregation-causing fluorescence quenching(ACQ)phenomenon and red shift of the emission spectra.This unique structure is conducive to the design of high-performance fluorescent materials.We synthesized a 4,5-(diphenyl)-spiro-[fluorene-9,2-imidazole]core via one-pot method,and modified it with various electron donors at the para positions of the imidazole's benzene ring and the meta positions of fluorenone in the spiro ring group,or used a spirocyclic as a substituent unit to replace with different positions of aromatic rings,and successfully synthesized a series of organic solid-state luminescent materials with spiro[fluorene-9,2-imidazole]as the core.Through various testing and characterization of the photoelectric properties of the molecules,the relationship between the molecular structure and properties of these molecules was studied,and the potential applications of these functional molecules in the fields of imaging,detection,and electroluminescent devices were explored.This thesis is divided into three systems.The main contents and conclusions are as follows:(1)Fluorescence properties and application of D-A-D spirocyclic molecules substituted with diphenylamineo group or carbazolyl group.In this section,a simple one-pot method was used to synthesize the compound 4,5-(diphenyl)-spiro[fluorene-9,2-imidazole].Diphenylamine and carbazole were used as donor units to modify the imidazole ring of the spirocyclic compound.And two simple D-A-D-structured V-shaped compounds S-DPA and S-CZ were successfully synthesized.Compounds S-DPA and S-CZ have obvious twisted intramolecular charge transfer(TICT)characteristic and aggregation-induced emission(AIE)behavior due to the introduction of the electron donors diphenylamine and carbazole.UV-visible absorption and photoluminescence spectra showed that S-DPA has a large molar absorption coefficient as high as 32,000 M-1·cm-1 and a wide solvatochromism emission range(440-560 nm).S-DPA can sensitively respond to trace water content(0-3 vol.%)in dioxane with a red-shift of 50 nm,indicating better solvatochromism and water sensitivity.It also possesses good trace water detection effect in other common organic solvents such as tetrahydrofuran,N,N-dimethylformamide and acetonitrile.Due to the rigid structure of the spirocyclic compounds,these two compounds have good thermal stability.The temperature corresponding to 5 wt.%loss of S-DPA is as high as 440?,and the temperature for that of S-CZ is above 300?.The fluorescence of S-DPA can be quenched after the solution of S-DPA is fumed in an acidic solvent atmosphere due to the presence of triphenylamine group,and the fluorescence can recover following triethylamine fuming.Based on the results,S-DPA is studied as a fluorescent probe to detect acid substances with high sensitivity.(2)Synthesis,photoelectric properties and application of spirocyclic molecules with aggregation-induced emission.Herein,the meta positions of fluorenone were substituted with carbazole groups to afford compound F-CZ.The photoluminescence measurement of F-CZ in THF/H2O mixtures showed that F-CZ have obvious AIE characteristic.Based on this,fluorenone was replaced with 4,5-(diphenyl)-spiro[fluorene-9,2-imidazole]and a series of spirocyclic compounds named as SP-CZ,SP-PZ and SP-TPE,separately containing substituents carbazole,phenothiazine and tetraphenylethylene were prepared.Compared with F-CZ,the UV-Visible absorption spectra of these three compounds were blue-shifted about 30 nm owing to the decreaed electron-withdrawing capability of the spirocyclic core.The compounds SP-CZ,SP-FZ and SP-TPE have good thermal stability due to the rigid spirocyclic structure.The fluorescence spectra of SP-TPE in THF-water mixture solutions showed obvious AIE phenomenon due to the presence of tetraphenylethylene AIE prototype.SP-TPE was applied to fingerprint display due to better solid-state luminescence performance.Fingerprints with different materials were treated with superglue and immersed in a THF/H2O mixture solution of SP-TPE,and all the treated glass,metal and plastic substrates showed obvious blue-green fluorescent fingerprints under the UV-lamp irridiation.It shows that SP-TPE has a good potential value in fingerprint imaging.(3)Synthesis and properties of organic luminescent molecules with bispirocyclic structure.In this part,bispirocyclic compounds P-SP and PSZ-SP in which the two para positions of central phenyl and 2,1,3-benzothiadiazolyl groups are connected to 4,5-(diphenyl)-spiro[fluoren-9,2-imidazole]structures were successfully synthesized using Pd-catalyzed Suzuki coupling reaction.PSZ-SP has a D-A-D structure with the central 2,1,3-benzothiadiazole group as strong electron-acceptor and the exterior spirocyclic part as electron donor.The UV-visible absorption spectrum showed that the maximum absorption peak locating at 407 nm was ascribed to the n-?*transition from intramolecular charge transfer(ICT).Fluorescence spectra showed that the two molecules showed good luminescence properties in both solid and solution states,and the orange fluorescence emission peak of PSZ-SP at 560 nm helped us to synthesize near-infrared fluorescence molecules.This bipirocyclic structure shows high potential value in many fields.