Design,Synthesis And Photophysical Properties Of Organic Small Molecular Room-temperature Phosphorescent Materials

Room-temperature phosphorescent?RTP?materials with easy structural functionalization and abundant species have attracted growing attention for researchers.Traditional RTP materials are mostly based on inorganic compounds,which possess many disadvantages,such as limited variety,high cost,poor processability,large brittleness,poor flexibility and easy damage and unsuitability for large area preparation.The application has been limited owing to the above shortcoming.The organic RTP materials are simple to synthesize,low in costs,and the luminescent lifetime is increased by several orders of magnitude compared with traditional RTP materials.They possess large stokes shifts,easily adjustable excited state and responsiveness to the environment,providing them as a promising class of materials in organic optoelectronics.So far,the field is still in the initial stage,and achieving efficient organic RTP emission at room temperature is necessary.Therefore,this thesis focuses on the design and synthesis of organic RTP materials,explores their luminescent mechanism and realizes their functional application,to develop organic RTP materials with excellent photophysical properties.The luminescent mechanism of organic RTP materials were explored to provide guide for their structural optimization and functional application.The major contents of the thesis include the following parts:1.Design and synthesis of different halogen substitution-based indole derivatives for room temperature phosphorescent materialsIn this chapter,based on the indole ring,the elements H,Cl,Br and I were introduced into the five positions of the indole benzene ring,and the compounds 5-H,5-Cl,5-Br,5-I,6-F,6-Cl,6-Br and 6-I were obtained.The structure of the compound was confirmed by NMR spectroscopy,and the crystals of five compounds were grown by recrystallization.Among them,5-Cl,6-F,6-Cl and6-Br possess long RTP emission lifetime with visible naked eye.Then,we measured the photoluminescence spectra,phosphorescence spectra and transient fluorescence spectra of the compounds.Combining with crystal data,the regulation of photophysical properties of compounds by the introduction of different halogens was analyzed.As the increasing of halogen atoms,heavy atom effect enhances spin orbit coupling,improving the inter-system crossing from the single state to the triplet state?S₁-T₁?,so as to promote the generation of triplet state and reduce the radiation transition of T₁-S₀.Thus,it improves the phosphor rate constant and phosphorescent quantum yield,showing that the phosphorescent efficiency of 5-I and 6-I was increased and the phosphorescent lifetime was reduced.Beside,the electronic effect of halogen atoms plays an important role in the tuning of photophysical properties.As compared with 6-Cl and 6-Br,the compound 6-F shows phosphorescent emission red-shifted,and fluorescence emission exhibits blue-shifted.This phenomenon shows that the electron withdrawing groups have different effects on stabilizing the triplet excited state and the single excited state for these compounds,in which the fluorine atom is benefit to stabilize the lowest triplet excited state.Finally,the digital encryption was realized through the different phosphorescence lifetime of compounds 6-Br and 6-I.After the introduction of halogen atoms,the phosphorescence spectra and fluorescence spectra of the eight compounds caused the phosphorescence emission red-shifted and the phosphorescence lifetime at room temperature was greatly reduced.By the introduction of different halogens,the fluorescence and phosphorescent emission spectra and wavelengths are also affected by their substitution in different positions.Due to the different electron cloud density distribution,5-substitutions and 6-substitutions of indole derivatives possess diffenent optical properities,the spectrum of 6-substitutions halogen compounds have a significant blue-shifted.In the end,the single crystal shows?-?stacking and C-H···?,the electron withdrawing effect of the F atom reduces the density of indoles ring electron cloud in compound 6-F and thus has a stronger C-H···?interaction.While,the presence of halogen bonds in compounds 5-Cl,5-Br and 6-Cl are benefit to the reduction of molecular vibration and the nonradiation transition process.Therefore,through introducing different halogen atoms at the 5 and 6 positions of the indole ring,a series of RTP materials were constructed,which can be served as guide for developing halogen substitution of organic long-lived luminescent materials.2.Design and exploration of chiral room temperature phosphorescent materials doped with host and guestIn chapter two of this thesis,we have designed and synthesized four chiral RTP materials including R-1S,R-2S,S-1S and S-2S,which acted as guest doped in amorphous hydroxylated steroid matrix ?-estradiol,achieving chiral RTP emission.After the introduction of the same group,we think that R-type and S-type naphthol have similar excited state in the photoluminescence and phosphorescent spectra.Furthermore,the chiral binafenol with a doping ratio of 3% had the best optical performance,single-substituted compounds R-1S and S-1S exhibit similar emission wavelength and the g value could reach 10^-3 orders of magnitude,different spatial configurations made R-1S exhibit longer room temperature phosphorescent lifetime,reaching 481 ms.No room temperature phosphorescent emission was observed in the doping system of disubstituted binaphthol,suggesting that the hydrogen bond formed between the exposed hydroxyl mono-substituted mononaphthol and?-estradiol had an important effect on enhancing the emission of phosphorescent at room temperature.So far,the application of small molecule CRTP materials are relatively low,and the study in this chapter provides valuable guidine for the development of room temperature phosphorescent materials.