Study Of Purely Organic Room-temperature Phosphorescence Based On Heavy Atom Effect And Its Application

In recent years,phosphorescent materials have gradually become a hot spot of luminescent materials.Organic room temperature phosphorescent materials have attracted lots of researchers because of their advantages such as easy preparation,low cost and easy regulation of molecular structure.However,it is still a great challenge to design organic materials with high phosphorescent and long luminescence time because of the spin prohibition,the quenching of triplet exciton and the existence of non-radiative transition in the conversion between singlet and triplet states.In this paper,the phosphorescent emission changes,mechanism explanation and related application of heavy atoms in organic molecules are discussed through two studies.（1）Two pure organic room temperature phosphorescent probes（ICz VM and Cz VM）targeting mitochondria of cells were designed and synthesized,using carbazole derivatives with or without heavy atoms and 1,4-dimethylpyridine iodide.Both probes have carbon-carbon double bonds and therefore have viscosity response properties that enhance fluorescence emission with increasing glycerol volume fraction in the glycerol/water system.This viscosity response property is controlled by temperature.TMB colorimetric method was used to verify that the two phosphorecent probes could produce singlet oxygen（¹O₂）under light.The quantum yield of singlet oxygen of ICz VM and Cz VM were respectively calculated as 37.05%and 23.68%,with MB as the reference standard,by DPBF UV absorption method.Comparing the quantum yields of the two,it is verified that the introduction of heavy atoms can improve the formation capacity of the singlet oxygen.In addition,according to the apoptosis-inducing properties of ¹O₂,a photodynamic antibacterial application was introduced.（2）In this work,four kinds of heavy atom phosphorescent compounds were preliminarily screened and the best organic room temperature phosphorescent compound BFCz B was studied.This compound was white powder under ambient conditions,and can emit a bright yellow phosphorescence when the UV lamp was turned on.The maximum excitation at 366 nm and the corresponding maximum emission at 544 nm,and two shoulder peaks at 590 and 640 nm,respectively,were observed.The lifetime was fitted as 103.55 ms and the afterglow was close to 2 s.To explore the influence of heavy atom introduction on phosphorescence,a theoretical simulation was performed by（TD）DFT.The band gap of HOMO/LUMO was only0.02 e V,which indicated that the molecule was easily excited.Compared with similar halohaline-free compounds,It is proved that the introduction of heavy atoms is helpful to increase the rate of spin-orbit coupling（SOC）and intersystem crossing（ISC）between singlet and triplet states.XRD spectroscopy was performed,for further exploring the origin of BFCz B ultralong phosphorescence,to investigate the molecular packing model and the presence of interactions.In BFCz B molecules,three types of intramolecular interactions,including C-Br···π（3.3731?）halogen bond,C-Br···N（3.1705?）halogen bond and C-F···H-C（2.5877?）hydrogen bond were observed,which effectively limited the rotation and vibration of the molecules,thereby reducing the non-radiative energy attenuation.In addition,some intermolecular interactions between halogen atoms and adjacent molecules were found in BFCz B.C-F formed major interactions with the carbazole rings of neighboring molecules,C-F···H-C（2.5271?）hydrogen bond and C-F···π（2.9335 and 3.0494?）halogen bond.C-Br···H-C（2.8466?）hydrogen bond and C-Br···π（3.5314?）halogen bond were also observed between Br and its neighbors.π···πstacking（3.3992?）were found in the carbazole group of the neighboring molecule.All these intramolecular and intermolecular interactions worked together to inhibit molecular motion,thereby further reducing the nonradiative attenuation of triplet excitons and achieved ultra-long phosphorescence.Moreover,in this work,the production of singlet oxygen（¹O₂）during phosphorescence of BFCz B molecular quenching in water was verified by the TMB colorimetric method,therefore,the photodynamic antibacteria were carried out.