10:30am - 11:00amInvited
Synthesis and Multi-chromic Characteristics of Oligoene-bridged Polycyclic Aromatic Hydrocarbons
Nagoya University, Japan
Polycyclic aromatic hydrocarbons (PAHs), small fragments of graphenes, have attracted significant attentions as optical and electronic molecular materials. Due to the large and planar π-surfaces of PAHs usually prompt aggregation-caused fluorescence quenching (ACQ), resulting in low emission efficiency. Here, we developed PAH-based fluorophores, which exhibited multi-chromic behaviors both in solution and solid state.
On the first topic, we prepared pyrenyl-substituted 1,3-butadienes bearing alkyl and aryl groups by palladium-catalyzed addition of 2-borylpyrene to internal alkynes. On UV irradiation, 1-pyrenylbutadienes undergo photochromism in solution. In the solid state, 1-pyrenyl-1,2,3,4-tetraaryl-1,3-butadiene exhibits red-shifted and broad emission as compared with the alkylated butadiene. The charge-carrier mobility of 1-pyrenyl-1,2,3,4-tetraalkyl-1,3-butadiene is higher than that of the arylated butadiene. Next, we synthesized dicyanoetheno-bridged hexa-peri-hexabenzocoronene (HBC) dimers through oxidation of a dicyanomethyl substituted HBCs. These dimers exhibited emission in solution. In the solid state, the emission efficiencies of the dimers were increased, exhibiting bright red emission. Intramolecular charge transfer interactions between the HBC units and the dicyanoethene bridge induced solvatochromic behavior in their emission spectra. Dicyanoetheno-bridged HBC dimers exhibited cis-trans photoisomerization behavior in the solution, affording the mixture in cis-isomer dominance at the photostationary state. In addition, we also prepared dicyanoethano-bridged dimers. This dimers exhibited mechanochromic behavior in solid state. After smearing, absorption band in the near IR region was generated. ESR analysis indicated the generation of radical species, that makes novel transition at NIR region. In this presentation, we will report the preparation, structures and multi-chromic behaviors of these dimers.
11:00am - 11:15amOral
Restricted Access to a Conical Intersection (RACI) Model to Explain AIE in Molecules
1University of Girona, Spain; 2Beijing Institute of Technology, China
Understanding the molecular mechanism behind AIE is crucial for the design of more efficient luminogens. Here we will present our recently developed RACI model. According to this model, AIE in some molecules is due to the fact that, in solution, the excited molecule undergoes fast decay to the ground state through a conical intersection (CI) involving a large amplitude motion. In the aggregate phase, this motion is blocked, ie access to the CI is restricted, and the molecule fluoresces. The RACI model is consistent with other models like restriction of intramolecular rotation (RIR) or intramolecular motion (RIM), but it allows to determine the modes that are responsible for loss of fluorescence in solution, namely those that lead to the CI. These are the coordinates that have to be blocked for fluorescence to occur. We will review our work on diphenyl benzofulvene (Li et al, Chem. Comm. 2013, vol. 49, p. 5966) and tetraphenyl dimethyl silole (Peng et al, J. Mat. Chem. C 2016, vol. 4, p. 2802) and present new results on tetrabenzoheptafulvalene derivatives.
11:15am - 11:30amOral
Fluorescent Porous Organic Frameworks Containing Molecular Rotors for Chemical Sensing
National University of Singapore, Singapore
Fluorescent porous materials have been under intensive investigation recently, because of their wide applications in molecular recognition and chemical sensing. Herein, we report a series of porous organic frameworks (POFs) containing flexible tetraphenylethylene (TPE) moieties as molecular rotors with responsive fluorescent behavior. These fluorescent POFs exhibit size-selective turn-on fluorescence for the effective chemical sensing of volatile organic compounds (VOCs), which can be attributed to the different degrees of motion restriction of flexible TPE rotors by various VOCs, leading to the partially freezing of rotors in more fluorescent conformations. Significantly, a linear aggregation-induced emission (AIE) relationship is observed between the fluorescent POFs and the VOCs over a wide range of concentrations, which is highly beneficial for quantitative sensing applications. The gas-phase detection of arene vapors using POFs is also proven with unprecedentedly high sensitivity, selectively, and recyclability. Furthermore, the POFs NUS-24 2D nanosheets demonstrate high selective and sensitivity for Fe3+ sensing over a wide range of metal ions, which is highly beneficial for environmental monitoring or biochemical applications. The mechanism of responsive fluorescence in POFs is further investigated using molecular simulations and density functional theory (DFT) calculations.
11:30am - 12:00pmInvited
Flexible and Highly Fluorescent Aromatic Polyimides: Design, Synthesis, Properties, and Mechanism
Sun Yat-sen University, China
High-tech display revolutions are attracting interest and have been rapidly developed. As one of their most powerful motivators, flexibility shows much more practical value of applications in our daily life, such as wearable devices and smart-phones with bendable or even foldable screens. Among the key materials for the vision of superior performance in flexible display, polymeric light-emitting materials is one of the most important fields due to their flexible nature and facile film formation by spin-coating or inkjet printing. However, the solubility, thermal stability, dimensional stability at high temperature, and photochemical stability of ordinary polymers seriously restrict their applications in large-area display devices.
On the other hand, polyimide (PI), is one of the representatives of high-performance engineering plastics, possessing several merits, such as excellent thermal stability, chemical and radiation resistance, tunable dielectric property and facile film-forming characteristics, and is becoming hot spot in optoelectronic fields. However, traditional PIs having intense intramolecular and intermolecular charge transfer (CT) characteristics between diamine moieties and dianhydride moieties significantly quench the fluorescence of PIs. Several attempts had been made, including the introduction of fluorescent chromophores into the backbone and side chain, or the utilization of alicyclic monomers, in order to obtain fluorescent PIs. However, the strong π-π interactions occurred between chromophores caused fluorescence quenching.
Here we would like to introduce the recent advance in the research of flexible and highly fluorescent aromatic polyimide in our lab, by proper regulating the intramolecular and intermolecular charge transfer effect on the molecular level, and discussing the mechanism based on the experimental results and the help of theoretical calculation.