Synthesis And Properties Of Star-shaped Pure Organic Room Temperature Phosphorescence Materials

Room-temperature phosphorescence(RTP)materials have received considerable attention recently owing to their promising applications in varying fields,including sensing,imaging,information security,organic light-emitting diodes,etc.However,the non-radiative transition of triplet excitons in pure organic RTP materials is relatively serious,and the intermolecular interaction in the crystalline state can effectively suppress the non-radiative transition.Therefore,a lot of pure organic RTP materials reported so far can only emit phosphorescence in the crystalline state.However,the poor reproducibility,processability,and flexibility of these crystal-based materials will greatly hinder their further development.Especially,the preparation of their thin films is always a critical and challenging task,while thin films with desirable optical properties are highly desired for many important practical applications.In this thesis,star-shaped emitters were designed and synthesized,and the non-radiative transition can be effectively suppressed by the large steric hindrance of the emitters itself,so as to obtain materials that can emit RTP in the film state.The main contents are as follows:1.TPM-4CHO,TPM-2CHO and TPM-4Br were designed and synthesized using tetraphenylmethane as the skeleton of star-shaped emitters and modified with aldehyde groups and bromine atoms.TPM-4CHO and TPM-2CHO,which contain aldehyde groups and tetraphenylmethane skeleton,exhibit rare solution-state RTP emission.TPM-4Br and p-tolualdehyde(TA),the segment of TPM-4CHO,only exhibit fluorescent in solution.This indicates that the large sterically hindered tetraphenylmethane skeleton and aldehyde groups play a key role in the realization of RTP in solution.Meanwhile,TPM-4CHO,TPM-2CHO and TPM-4Br achieved RTP in both doped and neat film states.The TPM-4CHO in neat film state has the highest phosphorescence quantum efficiency,which is 2.2%.The TPM-2CHO in neat film state has the longest phosphorescence lifetime of 7.26 ms.At the same time,the luminescence properties of the three materials in the crystalline state has been researched.They all have room temperature phosphorescence emission in the crystalline state,and the crystal of TPM-2CHO exhibits the longest lifetime of 7.70 ms and the highest phosphorescence quantum efficiency of 2.4%.Theoretical calculation and single crystal structure analysis show that the tetraphenylmethane skeleton has a large steric hindrance effect,which can effectively inhibit the nonradiative transition process;the aldehyde group can enhance the spin-orbit coupling and promote the formation of triplet excitons,which play key roles for the realization of solution-state room temperature.The strong intermolecular interactions in TPM-2CHO crystals are result in the best crystalline phosphorescence properties.2.Three benzene-cored star-shaped materials containing both O,S and Se atoms and carbazolyl moieties(CzO,CzS and CzSe)were designed and synthesized,which not only exhibit persistent RTP in crystal states,but also in doped and neat film states.In PVA films,with the enhancement of the heavy atom effect,the phosphorescence lifetimes are continuously shortened to 626 ms(CzO),480 ms(CzS)and 142 ms(CzSe).Theoretical calculations show that the spin-orbit coupling constants between T1 and So increase in the order of oxygen,sulfur and selenium,respectively:0.92 cm-1(CzO),13.34 cm-1(CzS)and 106.16 cm-1(CzSe).The large spin-orbit coupling constants accelerate radiative transitions of the phosphorescent,which may be the reason for the shortening of the τp.Meanwhile,the three materials also exhibit RTP emission in neat film state with afterglow.The τP of CzO,CzS and CzSe neat films are 328 ms,356 ms and 150 ms.It is worth noting that CzS in neat film also exhibits a visible afterglow in air with the lifetime of 166 ms,meanwhile the τP of CzO,CzSe is 36 ms and 53 ms.3.Four benzene-cored star-shaped materials containing both carbonyl groups and sulfur atoms(BPSP,BPSP-CH3,BPSP-OCH3 and BPSP-CF3)were designed and synthesized,which not only exhibit persistent RTP in crystal states,but also in doped and neat film states.The ΦP of the four materials in the doped films are extremely low(less than 1%).However,ΦP in the crystalline state are up to 18.9%.In order to further suppress the nonradiative transition,fused planar molecules FBPSP and FBPSP-CH3 were obtained.They all have RTP in solution,doped film,neat film and crystalline state.The planar conjugated molecular structures are prone to compact π-π stacking,thus their phosphorescence emission in pure film and crystalline state is significantly low.However,due to the improvement of the rigidity of the molecule itself,the phosphorescence of FBPSP and FBPSP-CH3 is significantly enhanced in the doped film,and the ΦP of FBPSP is as high as 47.0%,and the τP is as long as 24.75 ms.