Synthesis And Properties Of Luminescent Materials Based On Thiadiazole Quinoxaline

In the rapidly developing 21 st century,Organic light-emitting diodes(OLEDs)technology is rapidly replacing liquid crystal displays(LCDs)display technology,leading the development of today’s lighting display field,as OLEDs are thinner,lighter,and brighter than any glassbased displays,and offer better contrast,wider color range,viewing angles,and faster response times(higher refresh rates)compared to LCDs and plasma displays.The lack of a backlight system,which is a basic component of LCDs,simplifies the design structure and significantly reduces the size.However,OLEDs technology still face significant challenges.Firstly,a key factor in achieving high-performance OLEDs is the design and synthesis of advanced polymer and small molecule emissive materials with appropriate electrical and optical properties to fully harness the energy conversion capabilities of singlet and triplet excitons.Secondly,the utilization of charges is also affected by the charge injection processes,which are primarily determined by the electrical properties of the transport materials and device structure.Furthermore,the device structure simultaneously impacts the operating voltage and luminous efficiency of OLEDs,posing another major challenge in designing suitable structures.In the field of fingerprint recognition,organic fluorescent powder materials with simple molecular structures,strong fluorescence emission,long emission wavelength,and large Stokes shift are highly beneficial for visualizing latent fingerprints(LFPs).These materials greatly aid forensic investigations in confirming the identity of potential suspects.The electron-deficient and planar π-conjugated properties of the thiadiazole quinoxaline unit make it an ideal material for constructing low-bandgap small molecule and polymer semiconductors.Combining the above properties with the advantages of easy preparation and structural diversity,thiadiazole quinoxaline is considered an attractive chromophore for use in fluorescent probes,bioimaging,organic photovoltaic cells,organic field-effect transistors,and OLEDs.In the first part,two thiadiazole quinoxaline derivatives,TQ-TRZ and TQ-2Cz,were designed and synthesized through Suzuki coupling.The correctness of the structures of TQTRZ and TQ-2Cz was verified by proton nuclear magnetic resonance,carbon nuclear magnetic resonance,and high-resolution mass spectrometry.Then,the photophysical properties,electrochemical properties,and thermal stability of TQ-TRZ and TQ-2Cz were tested.TQ-TRZ emits orange-yellow light in dichloromethane solution with a fluorescence quantum yield of99%,and red light in solid films with a fluorescence quantum yield of 7%;TQ-2Cz emits red light in solution with a fluorescence quantum yield of 12%.In addition,both TQ-TRZ and TQ-2Cz have good thermal stability,and their thermal decomposition temperatures at 5% weight loss are 375 and 385 ℃,respectively.LFPs visualization experiments were carried out with TQ-TRZ,and the first and second features of fingerprints as well as the 1-3 level structural characteristics of LFPs were clearly observed on various non-porous surfaces,indicating that TQ-TRZ is an excellent material for preparing LFPs images.Therefore,TQ-TRZ and TQ-2Cz have certain research significance and development prospects in the fields of OLEDs,fluorescent probes,fingerprint recognition,and photosensitizers.In the second part,two thiadiazole quinoxaline derivatives,TQ-NIt Bu and TQ-NIMe,were designed and synthesized through Suzuki coupling.The structures of TQ-NIt Bu and TQNIMe were verified by nuclear magnetic resonance(NMR)spectroscopy,high-resolution mass spectrometry(HRMS)and NMR carbon spectroscopy.Subsequently,the photophysical properties,electrochemical properties,and thermal stability of the compounds were tested.TQNIt Bu emits orange-yellow light in dichloromethane solution and solid film,with fluorescence quantum yields of 8% and 5%,respectively;TQ-NIMe emits orange-yellow light in solution,with a fluorescence quantum yield of 62%,and emits orange-red light in solid film,with a fluorescence quantum yield of 0.1%.In addition,both TQ-NIt Bu and TQ-NIMe exhibit good thermal stability,with thermal decomposition temperatures at 5% weight loss of 384 and 403 ℃,respectively.LFPs visualization experiments were conducted on TQ-NIMe,which showed that the first and second level features of fingerprints could be clearly observed on various nonporous materials,and the 1-3 level structural features of LFPs could be clearly seen.Therefore,both TQ-NIt Bu and TQ-NIMe have certain research significance and development prospects in the fields of OLEDs and fingerprint recognition.In the third part,two thiadiazole quinoxaline derivatives,TQ-PPM and TQ-PM,were designed and synthesized by Suzuki coupling.The structures of compounds TQ-PPM and TQPM were characterized and verified by proton nuclear magnetic resonance,carbon nuclear magnetic resonance,and high-resolution mass spectrometry.Subsequently,their photophysical properties,electrochemical properties and thermal stability were tested.Both TQ-PPM and TQPM emitted orange-yellow light in dichloromethane solution and orange-red light in solid thin films.In addition,both TQ-PPM and TQ-PM exhibit good thermal stability,with thermal decomposition temperatures at 5% weight loss of 406 and 375 ℃,respectively.LFPs visualization experiments were carried out using TQ-PM,and clear first and second-level fingerprint features as well as 1-3 level structure features of LFPs could be observed on various non-porous surfaces.Therefore,both TQ-PPM and TQ-PM have certain research significance and development prospects in the fields of OLEDs and fingerprint recognition.