Aggregation-induced emission(AIE)luminescent materials are non-emissive in solution but highly emissive in aggregate state like crystal,powder and film.AIE materials can be divided into two categogries,fluorescent AIE system and phosphorescent AIE system,according to emission type.After over 20 years of development,AIE materials are widely recognized in photoelectronics,information sensing and bioimaging.Currently,the majority of AIE luminogens are aromatic organic molecules conjugated through bonds and the emission can cover visible and near infrared region with prominent properties.Meanwhile,the aromatic groups in AIE molecules can interact with each other through space so that effective through-space conjugation is formed.Though through-space conjugation has effect on the performance of luminescent materials due to the complicated excited state relaxation process,different multiplet emission system and weak through space electron communication,the impact of though-space conjugation on the performance of aromatic luminescent materials lacks of systematic research to study the mechanism.Therefore,the theme of this dissertation is to study the impact of through-space conjugation on the performance of aromtic organic solid-state luminescent materials.The details of this study are as follow:To confirm the influence of through-space conjugation on the performance of organic luminescent materials,two macrocyclic molecules 1a and 1b composed of tetraphenylethylene(TPE)units solely have been prepared through Suzuki reaction to study their photoluminescent properties.Because of the TPE units,both 1a and 1b exhibit excellent AIE properties.However,there’re subtle distinctions between the photoluminescence(PL)spectra of 1a and 1b due to the introduction of methyl in 1b.When the water volume fraction of the mixed solvent is above 60%,the PL peak of 1a red-shifts.The red-shift is the result of morphology of 1a aggregates changing from fibrous crystals to irregular particles.1a molelcules adopt a more through-sapce conjugated conformations in the irregular particles so that the energy gap decreases and the emission red-shifts.Nevertheless,the emission of 1b does not exhibit polymorphism-dependent red-shift due to the better solubility and increased steric hidrance.After confirming the influence of through-space conjugation on the fluorescent properties of organic solid-state materials,the study of the impact of through-space conjugation on the phosphorescent materials is conducted.Through-space conjugated phosphorescent materials XP2T,XP2F and XPC bridged by 9,9-dimethylxanthene have been prepared through Ullmann coupling reaction and Suzuki reaction.According to single crystal XRD analysis,the donor and acceptor are aligned cofacially with a distance short to 3.20(?).At room temperature,XP2T,XP2F and XPC crystals emits nearly pure phosphorescence with phosphorescence ratio of 97%,86%and 99%,respectively.On the basis of analysis and comparison of PL spectra and decay curves,the phosphorescence solely originates from phenothiazine group.Supplemented with spin-orbital coupling(SOC)matrix calculation and energy level calculation,a concept of through-space conjugation SOC is proposed.When S1 of donor and Tn of acceptor are degenerate in a through-space conjugated system,the through-space conjugation between the donor and acceptor can facilitate SOC,enhance the rate of intersystem crossing(k ISC)and phosphorescence-emitting performance.The k ISC of XPC is up to 1.2×109 s-1 owing to the highly efficient through-space conjugation SOC.The study of through-space heavy atom is carried out after demonstrating the facilitating effect of through-space conjugation on SOC and phosphorescence-emitting properties of organic materials.Hydrogen or halogen atom substituted phenothiazine derivatives XPH,XPF,XPCl,XPBr and XPI which are bridged by 9,9-dimethylxanthene were prepared to study the influence of through-space heavy-atom effect on the performance of luminescent materials.The substituted atom and the triplet exciton generating center phenothiazine group are bridged by 9,9-dimethylxanthene.Heavy-atom effect has a significant impact on PL properties of the crystal materials.The ratio of phosphorescence in steady-state PL spectra for XPBr crystal is 93%,while the ratio is 62%for XPCl and 75%for XPI.The phosphorescence lifetime of XPBr crystal is 5.8 ms,while the lifetime is 0.8 ms for XPCl and 0.1 ms for XPI.Heavy-atom effect is imposed on phenothiazine group by through-space p-πconjugation according to single crystal analysis.Br atoms in XPBr crystals can facilitate intersystem crossing of phenothiazine group and the through-space p-πconjugation between Br atom and phenothiazine group can stabilize triplet excitons and keep the rate of triplet exciton radiative transition(k P)and rate of non-radiative transition(k TS)lower than XPCl and XPI,while the strong through-space heavy-atom effect of I atom makes k ISC,k P and k TS of XPI one order of magnitude higher than XPBr.Therefore,PL quantum yield and phosphorescence lifetime of XPBr crystal increased significantly due to the synergistic effect of through-space p-πconjugation and through-space heavy atom effect.Naphthalene is chosen as bridge group to study the influence of shorter distance through-space conjugation and through-space heavy-atom effect on the perforamce of luminescent materials.It is proved that through-space heavy-atom effect can quench the fluorescence of phenothiazine group in NPBr and NPI while through-bond heavy atom effect reduces the phosphorescence lifetime of naphthalene group by comparing PL spectra and time-resovled decay curves of NPH,NPBr and NPI.As for the naphthalene bridged through-space conjugated structure,triplet excitons of phenothiazine groups can either emit phosphorescence or transfer the energy to naphthalene groups.Phenothiazine groups in NP2F tend to emit phosphorescence by themselves,while phenothiazine groups in NP4T tend to transfer most of its triplet energy to naphthalene groups and emits phosphorescence with long lifetime.Meanwhile,the afterglow of NPH@PVA is up 3.2 s at room temperature.By studying the influence of through-space conjugation effect on the performance of materials,the mechanisms of novel AIE materials were explored,laying a solid foundation for the development and application of solid organic photoluminecent materials. |