C OVALENT O RGANIC F RAMEWORKS
Over the past half century, a large number of porous materials have been designed and synthesized. Since this groundbreaking discovery, the chemical synthesis of COFs has advanced significantly and they show great potential for functional exploration8,9.
D ESIGN AND S YNTHESIS
So the linkage of the COFs should be covalent bonds which can be formed, broken and reformed during polymerization. Schematic representation of the mechanochemical (MC) synthesis of TpPa-1 (MC), TpPa-2 (MC) and TpBD (MC).
F UNCTIONS AND P ROPERTIES
Schematic representation of the stacked crystalline structure of 2D COFs with pre-organized and embedded π-columns. The highly ordered stacking structure and periodic alignment of the π-columns give COFs a high potential in photoconductivity.
S COPE OF T HIS T HESIS
In this thesis are listed the measurements that were carried out by the collaborators: Dr. Jia Gao in our group performed the structural optimization using DFTB methods and contributed to the PXRD pattern simulation.
R EFERENCES
I NTRODUCTION
According to this notion, various two-dimensional π-electronic frameworks have been developed, which show unique semiconducting, 6 photoconductive,7 and charge transfer properties.5 On the other hand, highly ordered skeletal alignment, high surface area along with open The channel structure of 2D COFs provides an intriguing motive for exploring well-defined nanoreactors, thus exhibiting a high potential to develop high-performance heterogeneous catalysts. The first class of COFs is the boroxine- or boronate-ester-based COF, which shows high crystallinity and porosity due to the high reversibility of the boroxine- or boronate-ester-forming reactions.
R ESULTS AND D ISCUSSIONS
The XRD patterns showed that the Py-An COF was a crystalline material (Figure 2-6A, red curve). 1 (A) XRA profiles of Py-An-COF experimentally observed (red), Pawley refinement (blue) and their difference (black). B) XRA profiles of Py-An-COF observed experimentally (red), simulated using AA stacking (green) and AB stacking (orange).
C ONCLUSION
E XPERIMENTAL S ECTION
The mixture was kept at 120°C for 14 hours and then cooled to room temperature, yielding a light green precipitate. The reaction mixture was cooled to room temperature and the fluffy orange precipitate was collected by centrifugation.
R EFERENCES
I NTRODUCTION
In addition, the high stability of COF could enable the easy separation and reusability of heterogeneous catalysts for industrial applications. 2D COFs are composed of polygonal sheets that are layered with π-π stacking to form periodic π-columnar arrays and ordered one-dimensional (1D) channels in a predesigned manner. 1D channels enable 2D COFs to act as π-electron beds that catalyze organic transformations. Here, the author demonstrates the development of π-electron walls of 2D electronic COFs as catalytic beds for driving organic transformations.
[4 + 2] cycloaddition reactions, known as Diels-Alder reactions, are a class of thermally allowed reactions that occur at elevated temperature. Diels-Alder reactions are one of the cornerstone transformations in modern organic chemistry and are frequently used for the synthesis of. It has been found that the encapsulation of the reactants and their rearrangement in the confined space of the catalyst can make the DA reactions take place at a lower temperature with high yield.51-58 Several cages and MOFs have been designed and used as catalysts for the reaction DA .51-58 However, to my knowledge, there has been no report on Diels-Alder catalytic reactions using heterogeneous catalyst with excellent catalytic activity and reusability at ambient temperature.
Here, the author reports a strategy for developing π-electronic COFs as heterogeneous catalysts for the Diels-Alder reactions under ambient conditions.
R ESULTS AND D ISCUSSIONS
This result indicates that the Py-An COF facilitates the Diels-Alder reaction under ambient conditions. Porosity of Py-An COF after 4th cycle of use: nitrogen sorption isothermal curves measured at 77 K (solid symbols: desorption, empty symbols: . adsorption). Porosity of Py-An COF after 4th cycle of use: Profiles of pore size (black circle) and pore size distribution (red circle).
TGA curves of Py-An COF samples (black: as synthesized, blue: . after using the 4th cycle as catalyst). TGA curves of Py-An COF samples (black: as synthesized, blue: after using the 4th cycle as catalyst). reactants, which produce DA adducts. Time-dependent electronic absorption spectral change of ethanol solution of 9-hydroxymethylanthracene (0.1 mM) after addition of Py-An COF (10 mg).
Encapsulation Experiments were performed by adding the Py-An OF samples to the ethanol solution of 9-hydroxymethylanthracene (Figure 3-9).
C ONCLUSION
E XPERIMENTAL S ECTION
After completion of the reaction, the solid Py-An COF was removed using filtration, the reaction mixture was concentrated in vacuo and then subjected to 1H NMR spectroscopy using CDCl3 as solvent. After completion of the reaction, the COF sample was collected via centrifugation, washed with acetone (2 mL × 3) and dried under vacuum; the COF sample was then reused for the next reaction at ambient conditions. A mixture of 9-hydroxymethylanthracene (0.05 mmol), N-substituted maleimide derivative (0.05 mmol) and ethanol (3 mL) in a tube was stirred at room temperature, 1 bar.
After the reaction was complete, the reaction mixture was concentrated under vacuum and then subjected to 1 H NMR spectroscopy using CDCl 3 as a solvent. The products were purified by preparative TLC using silica gel as stationary phase and hexane/CH 2 Cl 2 mixture was used as eluent. The concentration of 9-hydroxymethylanthracene in solution is defined by the equation, cEtOH = c0It/I0, where c0 is the initial concentration of 9-hydroxymethylanthracene in EtOH. It is the intensity of UV absorption spectra at 364 nm t h after the addition of Py-En COF and I0 is the initial intensity of UV.
On the other hand, the concentration of 9-hydroxymethylanthracene in the pores of COFs is defined by the equation, cCOF = c0V0(I0-It)/(I0VgmCOF), whereas V0 is the volume of EtOH, Vg is the pore volume of Py -En COF , mCOF is the mass of Py-An COF.
R EFERENCES
I NTRODUCTION
Artificial light-harvesting antennae are essential for harvesting, capturing, and converting solar energy, the main source of green energy afflicting the low-energy-density Earth.1 Natural light-harvesting antennae and photosynthetic systems that develop well-defined circular chlorophyll structures for efficient harvesting of light and energy transfer serve as inspiration for artificial systems for organizing chromophores into a highly ordered structure and harnessing solar energy. Many supermolecules such as dendrimers, self-assembled organogels, porphyrin arrays, and donor-acceptor systems using DNA, polypeptide, or tobacco mosaic virus (TMV) templates have been developed for light energy harvesting.1-8 However, these molecular aggregates are difficult to the actual construction of devices and systems due to the limited degree of macroscopic organization. Porous materials have attracted much attention as an alternative platform for the construction of light-harvesting antenna materials.
It has been reported that silicate-based porous zeolites, conjugated microporous polymers (CMPs), and metal-organic frameworks (MOFs) can efficiently harvest light. Arenes, such as triphenylene, pyrene, anthracene, and π-macrocycles including porphyrinst and phthalocyanines have been used for the construction of 2D COFs with periodically aligned π-columns that facilitate charge carrier transport and improve photoconductivity. This spatial configuration could potentially be exploited to promote the transfer of excitation energy from the framework to nanochannels and enhance the luminescence of dyes in the nanochannels.
Here, the author reports the collection and transduction of light energy using covalent organic frameworks (COFs). The highly ordered and densely packed π-skeletons of COFs serve as an excellent light-collecting antenna to harvest photons and induce ultrafast and quantitative energy transfer to the acceptor molecules spatially confined within the nanochannel domains of the antenna COFs.
R ESULTS AND D ISCUSSIONS
Field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) were used to investigate the morphology of PPy-COF. It has been found that the emission band of PPy-COF is almost totally overlapped with the excitation band of [4-(dicyanomethylene)-. Thus, the electrochemical band gap (Eg) of PPy-COF is 3.16 eV, which is in the region of blue light.
Thus, the electrochemical band gap (e.g.) of PPy-COF is 1.84 eV, which is in the range of red light. Along this line, DCM was loaded into the pores of the PPy-COF and its contents were controlled to achieve controlled energy transfer. As the DCM content increased, the fluorescence lifetime of the PPy-COF decreased (Table 4-4), which indicated energy transfer without radiative process.
Fluorescence emission spectra of PPy-COF & DCM @ toluene (solid curve upon excitation at 370 nm, dotted curve upon excitation at 462 nm).
E XPERIMENTAL S ECTION
Using the non-local density functional theory (NLDFT) model, the pore volume was extracted from the absorption curve. The crystal structure of COF was determined using the density functional tight binding (DFTB) method including Lennard-Jones (LJ) dispersion. DFTB is an approximate density functional theory method based on the tight coupling approach and uses an optimized LCAO Slater-type minimal all-valence basis set in combination with a two-center approximation for the Hamiltonian matrix elements.
The Coulombic interaction between partial atomic charges was determined using the self-consistent charge (SCC) formalism. The resulting precipitate was collected by centrifugation, washed with anhydrous DMF and acetone, and dried at 120 ˚C under vacuum to give PPy-COF (44 mg) in 80% yield as a pale yellow solid. In a typical entrapment procedure, a mixture of PPy-COF (20 mg) and DCM in a 10 mL pyrex tube was degassed under high vacuum.
R EFERENCES
This thesis consists of the design, synthesis and functional exploration of new π-electronic two-dimensional covalent organic frameworks, with an emphasis on the development of new π-electronic molecular frameworks. In chapter 2, the author describes a protocol for the synthesis of a new π-electronic mesoporous imine-based covalent organic framework (COF) using 1,3,6,8-tetrakis(p-formylphenyl)pyrene ( TFPPy) and 2, 6-diaminoanthracene (DAAn) as building blocks. In chapter 4, the author describes the synthesis and functions of a 2D π-electronic COF by introducing chromophore into the nano-channels.
In summary, this thesis comprises the design, synthesis and functionalization of π-electron 2D covalent organic frameworks. Yang Wu, Hong Xu, Xiong Chen, Jia Gao, and Donglin Jiang, π-electron covalent organic framework catalyst: π-walls as catalytic beds for Diels-Alder reactions under ambient conditions. Yang WU and Donglin JIANG, Designing covalent organic frameworks for light harvesting and energy transfer.
Yang WU and Donglin JIANG, A 2D Covalent Organic Framework as a Heterogeneous Catalyst for Diels-Alder Reactions at Ambient Temperature.
