Excited-State Dynamics in Fully Conjugated 2D Covalent Organic Frameworks

Jakowetz, Andreas C.; Hinrichsen, Ture F.; Ascherl, Laura; Sick, Torben; Calik, Mona; Auras, Florian; Medina, Dana D.; Friend, Richard H.; Rao, Akshay; Bein, Thomas

doi:10.1021/jacs.9b03956

Cited by 105 publications

(104 citation statements)

References 40 publications

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“…Studies on such photoexcitation decay processes are of substantial importance for understanding fundamental principles and for realizing applications, and the amount of available literature is fairly large. Organic polymers, covalent organic frameworks (COFs), dendrimers, and molecular state studies often appear in the literature. The primary motivation for such photophysical studies is to build artificial photosynthetic materials, solid‐state lighting for displays, and optical sensors.…”

Section: Short‐lived Photoexcited State Of Chromophoresmentioning

confidence: 99%

Advanced Photoresponsive Materials Using the Metal–Organic Framework Approach

2019

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In recent years, a particularly attractive and novel strategy has become available for the fabrication of photoresponsive, porous, and crystalline molecular solids from appropriately functionalized chromophoric linkers. The crystallinity of these materials allows a rather straightforward description and analysis using theoretical methods, thus tremendously accelerating the design of novel materials. This new class of crystalline molecular solids is referred to as metal-organic frameworks, MOFs (or porous coordination polymers, PCPs). [1] MOFs are constructed from metal-/metal-oxo nodes and organic linkers (Figure 1). The incorporation of photoactive species into MOFs may be realized by using them as linkers (method L) or attaching them to a linker (method A), as shown in Figure 1a. In addition, the porosity of MOFs allows the loading of chromophoric compounds as guests (method G) into the pores of this interesting framework material.In this review article, we mainly focus on organic photoactive species, which are either simply loaded as guests into porous MOFs or used after appropriate functionalization as building blocks for the construction of the framework (methods L, A, and G). [2] It is important to note that in the context of photoresponsive behavior, MOFs carry a potential which by far exceeds that of nonporous coordination polymers. This is because simple loading of guest/solvent molecules of different size/polarity/functionality in the MOF pores can impart a large optical response, which is useful, e.g., for sensing applications. [3] As an example, the solvent-dependent optical response or solvatochromism [4] is illustrated in Figure 1b. Such effects cannot be realized for nonporous coordination polymers.The different types of photoresponsive molecules addressed in this review can be grouped into two classes. The first contains molecules where the structure remains essentially unchanged upon light-induced electronic excitation, and the second contains molecular species that change their structure or conformation upon absorption of photons (molecular switches).Light with a wavelength in the range 200-800 nm (6.2-1.5 eV) can excite a molecule to a transient excited electronic state. The transient state then decays to a low-energy state, either the parent ground state or another longer-lived excited state. Decay time scales are in the range 10 −12 -10 1 s, and the released energy can be radiative or nonradiative in nature. For many applications, nonradiative energy loss is unwanted, When fabricating macroscopic devices exploiting the properties of organic chromophores, the corresponding molecules need to be condensed into a solid material. Since optical absorption properties are often strongly affected by interchromophore interactions, solids with a well-defined structure carry substantial advantages over amorphous materials. Here, the metal-organic framework (MOF)-based approach is presented. By appropriate functionalization, most organic chromophores can be converted to function as linkers, which can coo...

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Section: Short‐lived Photoexcited State Of Chromophoresmentioning

confidence: 99%

Advanced Photoresponsive Materials Using the Metal–Organic Framework Approach

2019

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“…Most reported 2D COFs are isolated as insoluble and polycrystalline aggregates, which inhibits conclusive studies on these materials. 17 These limitations have led to samples that strongly scatter light, resulting in poor signal-to-noise in time-resolved measurements. Further, the small crystalline domain sizes produced by previous synthetic conditions created difficulties in distinguishing properties arising from defects and non-crystalline regions from those that resulted from the COF crystalline domains themselves.…”

Section: Introductionmentioning

confidence: 99%

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

Flanders¹,

Kirschner²,

Kim³

et al. 2020

Preprint

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<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>

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“…POFs with unique structures have been synthesized through diversep olymerization reactions and buildingu nits, thus affording ordered POF materials, such as covalent organic frameworks (COFs), [21][22][23][24][25][26][27][28][29][30][31] and porouso rganic cages (POCs), [32][33] as well as amorphous POF materials including conjugated microporousp olymers (CMPs), [34][35][36][37][38][39] hyper-cross-linked polymers (HCPs), [40,41] covalent triazine frameworks (CTFs), [42][43][44][45][46][47][48][49] polymers of intrinsic microporosity (PIMs), [50][51][52] and porous aromatic frameworks (PAFs). [53][54][55][56][57][58][59] These POF materials have shown great potentiali ng as storage, catalysis, contaminant removal, energy storage and conversion, molecular separation, and other applications.…”

Section: Introductionmentioning

confidence: 99%

Light Hydrocarbon Separations Using Porous Organic Framework Materials

Zhang

Taylor

Jiang

et al. 2019

Chemistry A European J

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Light hydrocarbons (C1–C3) are used as basic energy feedstocks and as commodity organic compounds for the production of many industrially necessary chemicals. Due to the nature of the raw materials and production processes, light hydrocarbons are generated as mixtures, but the high‐purity single‐component products are of vital importance to the petrochemical industry. Consequently, the separation of these C1–C3 products is a crucial industrial procedure that comprises a significant share of the total global energy consumption per year. As a complement to traditional separation methods (distillation, partial hydrogenation, etc.), adsorptive separations using porous solids have received widespread attention due to their lower energy costs and higher efficiency. Extensive research has been devoted to the use of porous materials such as zeolites and metal‐organic frameworks (MOFs) as solid adsorbents for these key separations, owing to the high porosity, tunable pore structures, and unsaturated metal sites present in these materials. Recently, porous organic framework (POF) materials composed of organic building blocks linked by covalent bonds have also shown excellent properties in light hydrocarbon adsorption and separation, sparking interest in the use of these materials as adsorbents in separation processes. This Minireview summarizes the recent advances in the use of POFs for light hydrocarbon separations, including the separation of mixtures of methane/ethane, methane/propane, ethylene/ethane, acetylene/ethylene, and propylene/propane, while highlighting the relationships between the structural features of these materials and their separation performances. Finally, the difficulties, challenges, and opportunities associated with leveraging POFs for light hydrocarbon separations are discussed to conclude the review.

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Excited-State Dynamics in Fully Conjugated 2D Covalent Organic Frameworks

Cited by 105 publications

References 40 publications

Advanced Photoresponsive Materials Using the Metal–Organic Framework Approach

Advanced Photoresponsive Materials Using the Metal–Organic Framework Approach

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

Light Hydrocarbon Separations Using Porous Organic Framework Materials

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