Synthesis,Crystal Structure And Photophysical Properties Of Novel AIE Materials With Color-Tunable Solid State Emission

As a key component in the organic light-emitting devices (OLEDs), the organic light-emitting materials largely affect the process of industrialization of OLEDs. The organic light-emitting materials are practically used as thin films in OLEDs, so it is of great significance to study and explore organic materials with highly efficient solid state emission. Aggregation-induced emission phenomenon (AIE) offers an effective approach for the development of highly luminous organic materials, and in the past decade a large number of AIE-active dyes based on the core-structure with silole or tetraphenylethene have been developed.The switching and tuning of organic solid-state fluorescence via chemical and/or physical methods and its mechanism is of great current interest. Mechanochromic fluorescent materials are a class of smart materials with fluorescent properties that change in response to external force stimuli, which could be used in memory chips, sensors, and security inks. However, organic mechanochromic fluorescent materials that are dependent on changes in physical molecular packing modes are extremely rare. This thesis mainly contributes to develop novel core-structures AIE fluorophores, and switch and tune these dyes’ solid-state emission through chemical modification or external stimuli. Its main contents summarized as follows.In chapter one, the photophysical processes of excited molecules are briefly introduced. The latest progress of organic small molecules with highly efficient solid-state emission and various strategies that have been effectively utilized to achieve switchable and tunable fluorescence in the organic solid state are reviewed.In chapter two, based on the structure of1,1,4,4-tetraphenyl butadiene, four polysubstituted2,2’-biindenyl fluorophores la,2a,3a and4a were designed and synthesized, and their optical properties in solution and solid-state were investigated. Compounds la-4a have the AIE nature. Single crystals of these dyes were obtained by slow solvent evaporation method. The large interplane angles in the cystals make the conformations of la-4a largely deviated from a planar conformation, which prevents molecules from p-p stacking interactions, and thus induces intense emissions in crystal state. The crystals of la-3a show intense blue luminescence, and4a green; while the amorphous film’s emission of la-3a red-shift to sky blue, and4a still green. This suggests that solid state emission of compounds la-3a depends on their molecular conformation and packing mode. The mechanochromic ability of la-3a was further examined, and the powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements were carried out to validate the mechanism of mechanochromism.In chapter three, based on the last chapter, in order to expand the emission of2,2’-biindenyl derivatives to red region and obtain the BODIPY fluorophore with highly efficient solid state emission, BODIPY moieties were innovatively incorporated into2,2’-biindenyl systems. Bodipy fluorophore BDY-IN was designed and synthesized. BDY-IN still has the AIE nature. Two kinds nano-particles of BDY-IN were prepared by reprecipitation, and they exhibited distinct emission which suggested that the emission of the nano-particles depends on BDY-IN molecular packing mode in the aggregate. The BDY-IN crystals with two polymorphic forms (BDY-O and BDY-R) have been obtained. Due to the more planar conformation and face to face p-p stacking interaction increasing the p-conjugated degree, the emission of BDY-R displays an obvious red shift about79nm compared with BDY-O.In chapter four, three fluorophores (CN-TPA,3CN-TPA and4CN-DTPA) containing triphenylacrylonitrile and triphenylamines moieties were designed and synthesized. These three dyes are all AIE-active, and CN-TPA display mechanochromism in solid phase. Grinding could disrupt the crystalline CN-TPA with blue-green emission into amorphous CN-TPA with yellow-green emission, and heating treatment could change the amorphous CN-TPA into crystalline CN-TPA. Powder X-ray diffraction (PXRD) characterizations demonstrated that crystalline and amorphous CN-TPA possesses different molecular packing. A differential scanning calorimetry (DSC) measurement revealed that the emission switching was due to the exchange between the thermodynamic-stable crystalline and metastable amorphous states. Single crystals of CN-TPA were gotten by slow solvent evaporation method. The reason for the phase transformation caused by external pressure is ascribed to the twisted conformation of the molecule which leads to poor solid molecular packing and weak interactions in the interfaces of lamellar layers confirmed by its single-crystal X-ray diffraction analysis.In chapter five, the fused ring substituted N,N-diaryl phenazine derivatives were synthesized by generating two C-N bond in one step to form a ring. These compounds exhibit unnormal large Stocks shift up to240nm independent on the polarity of the solvent. Their solution show orange-red emission around600nm, while the solid powder in the blue and green region. Ml-flu was selected as a luminescent material used in organic light emitting diode (OLED).In chapter six, indenyl-modified9,10-diphenyl anthracene derivative IN A was designed and synthesized, and its photophysical properties were preliminary studied and compared with 9,10-bis(4-(2,2-diphenylvinyl)phenylanthracene (DPVA).In chapter seven, conclusion.