Large Exciton Diffusion Coefficients in Two-Dimensional Covalent Organic Frameworks with Different Domain Sizes Revealed by Ultrafast Exciton Dynamics

2020 ◽  
Vol 142 (35) ◽  
pp. 14957-14965 ◽  
Author(s):  
Nathan C. Flanders ◽  
Matthew S. Kirschner ◽  
Pyosang Kim ◽  
Thomas J. Fauvell ◽  
Austin M. Evans ◽  
...  
Keyword(s):  
Diffusion Coefficients ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
Exciton Dynamics ◽  
Exciton Diffusion

scholarly journals Ultrafast Exciton Dynamics in Two Dimensional Covalent Organic Frameworks Reveals Size Dependence to Exciton Diffusion

2020 ◽  
Author(s):  
Nathan C. Flanders ◽  
Matthew S. Kirschner ◽  
Pyosang Kim ◽  
Thomas Fauvell ◽  
Austin Evans ◽  
...  
Keyword(s):  
High Performance ◽  
Transient Absorption ◽  
Domain Size ◽  
Spectroscopic Techniques ◽  
Two Dimensional ◽  
Exciton Dynamics ◽  
Singlet Exciton ◽  
Exciton Diffusion ◽  
Absorption Studies ◽  
Exciton Annihilation

<p>Large singlet exciton diffusion lengths are a hallmark of high performance in organic based devices such as photovoltaics, chemical sensors, and photodetectors. In this study, exciton dynamics of a two-dimensional covalent organic framework, COF- 5, is investigated using ultrafast spectroscopic techniques. Following photoexcitation, the COF-5 exciton decays via three pathways: 1) excimer formation (4 ± 2 ps), 2) excimer relaxation (160 ± 40 ps), and 3) excimer decay (>3 ns). Excitation fluence-dependent transient absorption studies suggest that COF-5 has a relatively large diffusion coefficient (0.08 cm2/s). Furthermore, exciton-exciton annihilation processes are characterized as a function of COF-5 crystallite domain size in four different samples, which reveal domain- size dependent exciton diffusion kinetics. These results reveal that exciton diffusion in COF-5 is constrained by its crystalline domain size. These insights indicate the outstanding promise of delocalized excitonic processes available in 2D COFs, which motivate their continued design and implementation into optoelectronic devices. </p>

scholarly journals Ultrafast Exciton Dynamics in Two Dimensional Covalent Organic Frameworks Reveals Size Dependence to Exciton Diffusion

2020 ◽  
Author(s):  
Nathan C. Flanders ◽  
Matthew S. Kirschner ◽  
Pyosang Kim ◽  
Thomas Fauvell ◽  
Austin Evans ◽  
...  
Keyword(s):  
High Performance ◽  
Transient Absorption ◽  
Domain Size ◽  
Spectroscopic Techniques ◽  
Two Dimensional ◽  
Exciton Dynamics ◽  
Singlet Exciton ◽  
Exciton Diffusion ◽  
Absorption Studies ◽  
Exciton Annihilation

<p>Large singlet exciton diffusion lengths are a hallmark of high performance in organic based devices such as photovoltaics, chemical sensors, and photodetectors. In this study, exciton dynamics of a two-dimensional covalent organic framework, COF- 5, is investigated using ultrafast spectroscopic techniques. Following photoexcitation, the COF-5 exciton decays via three pathways: 1) excimer formation (4 ± 2 ps), 2) excimer relaxation (160 ± 40 ps), and 3) excimer decay (>3 ns). Excitation fluence-dependent transient absorption studies suggest that COF-5 has a relatively large diffusion coefficient (0.08 cm2/s). Furthermore, exciton-exciton annihilation processes are characterized as a function of COF-5 crystallite domain size in four different samples, which reveal domain- size dependent exciton diffusion kinetics. These results reveal that exciton diffusion in COF-5 is constrained by its crystalline domain size. These insights indicate the outstanding promise of delocalized excitonic processes available in 2D COFs, which motivate their continued design and implementation into optoelectronic devices. </p>

Seeded Growth of Single-Crystal Two-Dimensional Covalent Organic Frameworks

2017 ◽  
Author(s):  
Austin M. Evans ◽  
Lucas R. Parent ◽  
Nathan C. Flanders ◽  
Ryan P. Bisbey ◽  
Edon Vitaku ◽  
...  
Keyword(s):  
Molecular Transport ◽  
Controlled Synthesis ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
Seeded Growth ◽  
Covalent Bonds ◽  
Crystalline Materials ◽  
Step Procedure ◽  
Structures And Properties ◽  
2D Polymer

<div> <div> <div> <p>Polymerizing monomers into periodic two-dimensional (2D) networks provides structurally precise, atomically thin macromolecular sheets linked by robust, covalent bonds. These materials exhibit desirable mechanical, optoelectrotronic, and molecular transport properties derived from their designed structure and permanent porosity. 2D covalent organic frameworks (COFs) offer broad monomer scope, but are generally isolated as polycrystalline, insoluble powders with limited processability. Here we overcome this limitation by controlling 2D COF formation using a two- step procedure. In the first step, 2D COF nanoparticle seeds are prepared with approximate diameters of 30 nm. Next, monomers are slowly added to suppress new nucleation while promoting epitaxial growth on the existing seeds to sizes of several microns. The resulting COF nanoparticles are of exceptional and unprecedented quality, isolated as single crystalline materials with micron-scale domain sizes. These findings advance the controlled synthesis of 2D layered COFs and will enable a broad exploration of synthetic 2D polymer structures and properties. </p> </div> </div> </div>

Seeded Growth of Single-Crystal Two-Dimensional Covalent Organic Frameworks

2017 ◽  
Author(s):  
Austin M. Evans ◽  
Lucas R. Parent ◽  
Nathan C. Flanders ◽  
Ryan P. Bisbey ◽  
Edon Vitaku ◽  
...  
Keyword(s):  
Molecular Transport ◽  
Controlled Synthesis ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
Seeded Growth ◽  
Covalent Bonds ◽  
Crystalline Materials ◽  
Step Procedure ◽  
Structures And Properties ◽  
2D Polymer

<div> <div> <div> <p>Polymerizing monomers into periodic two-dimensional (2D) networks provides structurally precise, atomically thin macromolecular sheets linked by robust, covalent bonds. These materials exhibit desirable mechanical, optoelectrotronic, and molecular transport properties derived from their designed structure and permanent porosity. 2D covalent organic frameworks (COFs) offer broad monomer scope, but are generally isolated as polycrystalline, insoluble powders with limited processability. Here we overcome this limitation by controlling 2D COF formation using a two- step procedure. In the first step, 2D COF nanoparticle seeds are prepared with approximate diameters of 30 nm. Next, monomers are slowly added to suppress new nucleation while promoting epitaxial growth on the existing seeds to sizes of several microns. The resulting COF nanoparticles are of exceptional and unprecedented quality, isolated as single crystalline materials with micron-scale domain sizes. These findings advance the controlled synthesis of 2D layered COFs and will enable a broad exploration of synthetic 2D polymer structures and properties. </p> </div> </div> </div>

Pathway Complexity in the Stacking of Imine-linked Macrocycles Related to Two-Dimensional Covalent Organic Frameworks

2019 ◽  
Author(s):  
Shiwei Wang ◽  
Anton Chavez ◽  
Simil Thomas ◽  
Hong Li ◽  
Nathan C. Flanders ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Structural Similarity ◽  
Discrete Models ◽  
Side Chains ◽  
Two Dimensional ◽  
Assembly Process ◽  
Covalent Organic Frameworks ◽  
Electron Systems ◽  
Monomer Structure ◽  
Kinetic Traps

This work reports on the assembly of imine-linked macrocycles that serve as models of two-dimensional covalent organic frameworks (2D COFs). Interlayer interactions play an important role in the formation of 2D COFs, yet the effect of monomer structure on COF formation, crystallinity, and susceptibility to exfoliation are not well understood. For example, monomers with both electron-rich and electron-poor π-electron systems have been proposed to strengthen interlayer inter-actions and improve crystallinity. Here we probe these effects by studying the stacking behavior of imine-linked macrocycles that represent discrete models of 2D COFs. <div><br></div><div>Specifically, macrocycles based on terephthaldehyde (PDA) or 2,5-dimethoxyterephthaldehyde (DMPDA) stack upon cooling molecularly dissolved solutions. Both macrocycles assemble cooperatively with similar ΔHe values of -97 kJ/mol and -101 kJ/mol, respectively, although the DMPDA macrocycle assembly process showed a more straightforward temperature dependence. Circular dichroism spectroscopy performed on macrocycles bearing chiral side chains revealed a helix reversion process for the PDA macrocycles that was not observed for the DMPDA macrocycles. <br></div><div><br></div><div>Given the structural similarity of these monomers, these findings demonstrate that the stacking processes associated with nanotubes derived from these macrocycles, as well as for the corresponding COFs, are complex and susceptible to kinetic traps, casting doubt on the relevance of thermodynamic arguments for improving materials quality. <br></div>

Design and Synthesis of Two-Dimensional Covalent Organic Frameworks with Four-Arm Cores: Prediction of Remarkable Ambipolar Charge-Transport Properties

2019 ◽  
Author(s):  
Simil Thomas ◽  
Hong Li ◽  
Raghunath R. Dasari ◽  
Austin Evans ◽  
William Dichtel ◽  
...  
Keyword(s):  
Charge Transport ◽  
Organic Semiconductors ◽  
Density Functional ◽  
Polymer Networks ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
X Ray Diffraction ◽  
Zinc Porphyrin ◽  
Design And Synthesis ◽  
Predicted Values

<p>We have considered three two-dimensional (2D) π-conjugated polymer networks (i.e., covalent organic frameworks, COFs) materials based on pyrene, porphyrin, and zinc-porphyrin cores connected <i>via</i> diacetylenic linkers. Their electronic structures, investigated at the density functional theory global-hybrid level, are indicative of valence and conduction bands that have large widths, ranging between 1 and 2 eV. Using a molecular approach to derive the electronic couplings between adjacent core units and the electron-vibration couplings, the three π-conjugated 2D COFs are predicted to have ambipolar charge-transport characteristics with electron and hole mobilities in the range of 65-95 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>. Such predicted values rank these 2D COFs among the highest-mobility organic semiconductors. In addition, we have synthesized the zinc-porphyrin based 2D COF and carried out structural characterization via powder X-ray diffraction and surface area analysis, which demonstrates the feasability of these electroactive networks.</p>

Thermally conductive ultra-low-k dielectric layers based on two-dimensional covalent organic frameworks

2021 ◽  
Author(s):  
Austin M. Evans ◽  
Ashutosh Giri ◽  
Vinod K. Sangwan ◽  
Sangni Xun ◽  
Matthew Bartnof ◽  
...  
Keyword(s):  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
Dielectric Layers ◽  
Thermally Conductive ◽  
Low K

Two-Dimensional Imine-Linked Covalent Organic Frameworks as a Platform for Selective Oxidation of Olefins

2017 ◽  
Vol 9 (27) ◽  
pp. 22856-22863 ◽  
Author(s):  
Manman Mu ◽  
Yanwen Wang ◽  
Yutian Qin ◽  
Xilong Yan ◽  
Yang Li ◽  
...  
Keyword(s):  
Selective Oxidation ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
Oxidation Of Olefins

Piezoelectricity in two-dimensional covalent organic frameworks

2017 ◽  
Vol 121 (22) ◽  
pp. 225112
Author(s):  
Hui Xiang ◽  
Bo Xu ◽  
Yidong Xia ◽  
Jiang Yin ◽  
Zhiguo Liu
Keyword(s):  
Two Dimensional ◽  
Covalent Organic Frameworks
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