Click Architecture And Properties Of POSS-based Hybrid Light-emitting Materials

Organic light-emitting (OLE) materials have received considerable interest due to their low cost, large area preparation and easy modification via organic reactions for various demands. Because organic emission is molecular luminescence, OLE materials often possess rigid conjugated coplanar structures, and the rigid conjugated coplanax structures often result in molecular aggregation and luminescent quenching (ACQ) in solid state due to strong intermolecular π-π stacking interaction, which severely limits their practical applications. Wrapping is a simple physical method to conquer the aggregation effect of OLE molecules. Nevertheless, these resultant materials often suffer from their inherent reversibility during application due to the diffuse effect caused by molecular thermal motion, which further result in molecular aggregation. Hence, it is a great challenge to look for a highly efficient and stable controllable method to overcome the aggregation effect. In order to solve this problem, in this paper, we designed and prepared a series of POSS-based organic/inorganic hybrids (star-, tadpole-and dumbbell-type). And the disaggregation mechanism and optical/thermal stability enhancement mechanism of POSS was discussed in detail by experiment and theoretical calculation method.Click chemistry, based on Huisgen1,3-dipolar cycloaddition reaction between azide and alkyne, have attracted great attention owing to its high efficiency, good stereoselectivity, mild reaction conditions, insensitive to oxygen/water and so on. However, to the best of our knowledge, the triazole units as an electron-poor heterocycle conjugated bridges are utilized in D-π-A conjugated systems for investigating the influences of molecular structure on optical properties of resultant compounds, so far, are not understood. Hence, we designed and prepared four novel triazole bridge-linked fluorene derivatives with different terminal push/pull substituted groups. The influences of molecular structures and triazole moiety on intramolecular charge transfer in these optical materials, and the dependence of optical properties on molecular structure were investigated in detail by experimental and the theoretical simulation methods.In addition, preparation of organic white-light-emitting (WLE) materials is another research hotspots. WLE materials are desirable because of the potential applications in full-color displays and solid-state lighting sources. However, the organic white-light-emitting devices (WLEDs) contained multi component molecular emitters often show uneven color and color coordinates shift during actual use due to different degradation rate of each component. Utilization of a single white-light-emitting molecule will solve these problems. However, the design and preparation of single white-light-emitting molecules is still a big challenge.The main contents of this dissertation consist of the following points:1. The light emission, molecular aggregation and disaggregation mechanism of organic materials were systematically reviewed. The application of POSS and click chemistry in preparation of OLE materials and the development of WLE materials was also systematically reviewed.2. A novel eight-arm azido functional Q-type POSS precursor was designed and synthesized. From it a3D eight-arm star-type POSS-based organic/inorganic hybrid light-emitting nanoparticle was prepared through a controlled and efficient click chemistry methods.The results from the calculation of electron cloud density and mechanism research show that the introduction of nanometer-sized POSS effectively forbids the n-n stack of the organic components and prevents the aggregation induced quenching effect. The resultant nanoparticles show a strong fluorescent emission in solid state. Moreover, the introduction of inorganic POSS effectively improves the optical, thermal stability of the materials, the filmformability, and stability of the amorphous film.3. Tadpole-typed POSS-based hybrid molecules H1and dumbbell-shaped POSS-based hybrid molecules H2were efficient synthesized via click chemistry and their reference molecules (Ml and M2) were also synthesized. It is found fromdensity functional theory(DFT) theoretical simulation and luminescent mechanism research that the tadpole-type hybrid molecules stack with each other by the way of the boat-or chair-type after introduction of one POSS cage in the one end of the organic conjugate planar molecules. And the aggregation effect was weaken due to the distance increase between the organic component plan from...to..(chair-type),(boat-type) for M1to HI. On the contrary, in a dumbbell-shaped hybrids, which POSS cages are incorporated into two end of the organic component, the effective face-to-face π-π stack is difficultly formed due to the side by side stacking type. Thus, H2showed a good disaggregation effect, and the luminous efficiency is significantly improved.4. Four different triazole-bridged conjugated molecules with push/pull effect were designed and controllably prepared by click chemistry, and the relationships between the intramolecular charge transfer (ICT) and the influence of molecular structure on optical properties were discussed in details. It is found fromDFT theoretical simulation and luminescent mechanism research that ICT emission, ICT/LE mixture emission and LE emission were achieved by varying terminal group of triazole bridged conjugation from unsubstituted moiety (H, T1), donor units (CH3and OCH3, T2and T3) to accepter group (NO2, T4), respectively. Meanwhile, after introducing strong electron withdrawing substitutional group-NO2, a ground state CT absorption and only LE emission was observed. The results provide important foundation for the molecular design and development of novel optoelectronic materials in future.5. Based on the control mechanism of intramolecular energy transfer, a blue-light-emitting molecule (B) and a restriction of intramolecular rotation (RIR) induced yellow-light-emitting molecule (Y) were designed and synthesized. It is found from optimization experiments that a white-light-emitting molecule was precisely synthesized by click chemistry on the feed ratio of B:Y at6:2.The results of WLE mechanism indicate that the realization of WLE is attributed tothe precise control of intramolecular energy transfer and disaggregation effect of POSS. This provides a new strategy for the design and preparation of new single-molecule white materials.