Regioselective Substitution at the 1,3- and 6,8-Positions of Pyrene for the Construction of Small Dipolar Molecules

One-Pot Synthesis of Pyreno[2,1-b]furan Molecules with Two-Photon Absorption Properties

The development of large π-conjugated polycyclic heteroaromatic materials is of immense interest, both in the academic as well as the industrial community. Herein, we present the efficient one-pot synthesis of novel pyreno[2,1-b]furan molecules from a newly designed intermediate, which display intense green emission (505-516 nm) in solution and a large red shift emission (625-640 nm) in the solid state, because of strong π-π stacking. More interestingly, the compounds exhibit novel two-photon absorption (TPA) properties, and the TPA cross-section (δ) value was increased to 533 GM by regulating the electronic effects of the substituents of the pyreno[2,1-b]furan molecules. This study not only offers a facile strategy for constructing new pyrene-fused luminescence materials with two-photon absorption properties but also provides a new chemical intermediate that opens up a new pathway to advanced materials.

Intermolecular Hydrogen-Bond-Assisted Solid-State Dual-Emission Molecules with Mechanical Force-Induced Enhanced Emission

Hydrogen bonds not only play a crucial role in the life sciences but also endow molecules with fantastic physical and chemical properties, which help in the realization of their high-tech applications. This work presents an efficient strategy for achieving highly efficient solid-state dual-emission blue emitters with mechanical force-induced enhanced emission properties via intermolecular hydrogen bonds via novel pyrene-based intermediates, namely, 1,3,6,8-tetrabromo-2,7-dihydroxypyrene (1) and 1,3,6,8-tetrabromo-2-hydroxypyrene (2), prepared via hydroxylation and bromination of pyrene in high yields. Moreover, further use of a classical Pd-catalyzed coupling reaction affords new pyrene-based luminescent materials 3-5, which display high thermal stability (in range of 336-447 °C), blue emission (<463 nm), and high quantum yields in solution. Interestingly, with the monosubstituted hydroxyl (OH) or methoxy (OMe) group located at position 2 of pyrene, compounds 4a and 5 display exciting dual emission with mechanical force-induced enhanced emission properties, due to the presence of several hydrogen-bond interactions. Moreover, this series of compounds exhibits numerous advantages, for example, deeper blue emission with a narrower full width at half-maximum, a stronger steric effect, and higher hydrophilicity. Thus, these novel bromopyrene intermediates and related pyrene-based luminescent materials will pave the way for further exploration of novel organic solid-state luminescent materials for potential application in organic electronics, bioimaging, chemosensors, etc.

Synthesis and Properties of 1-Azapyrenes

A straightforward method for the synthesis of a series of hitherto unknown 1-azapyrenes is reported, which relies on a combination of Pd-catalyzed cross-coupling reactions with Brønsted acid-mediated cycloisomerization reactions. The methodology is highly modular and allows an efficient synthesis of various substituted products in high yields. The structural, electrochemical, and photophysical properties of 1-azapyrenes have been studied by ultraviolet-visible (UV-vis) and fluorescence spectroscopies, cyclic voltammetry, and density functional theory (DFT) calculations.

Synthesis of 2-Azapyrenes and Their Photophysical and Electrochemical Properties

A series of 5,7,9-substituted 2-azapyrenes were synthesized for the first time. The synthesis relies on Brønsted acid promoted benzannulation of alkyne precursors prepared by palladium-catalyzed cross-coupling reactions. The synthetic strategy is efficient and the scope covers a variety of functional groups. The electrochemical behavior and photophysical properties of the products were investigated by UV-vis and fluorescence spectroscopy, cyclic voltammetry, and DFT calculations.

Ab initio study on the excited states of pyrene and its derivatives using multi-reference perturbation theory methods

The excited states of phenyl-substituted pyrene derivatives were calculated using multi-reference perturbation theory methods.

Molecular Packing and Solid-State Photophysical Properties of 1,3,6,8-Tetraalkylpyrenes

The relationship between the photophysical properties and molecular orientation of 1,3,6,8-tetraalkylpyrenes in the solid state is described herein. The introduction of alkyl groups with different chain structures (in terms of length and branching) did not affect the photophysical properties in solution, but significantly shifted the emission wavelengths and fluorescence quantum yields in the solid state for some samples. Pyrenes bearing ethyl, isobutyl, or neopentyl groups at the 1-, 3-, 6-, and 8-positions showed similar emission profiles in both the solution and solid states. In contrast, pyrenes bearing other alkyl groups exhibited an excimer emission in the solid state, similar to that of the parent pyrene. On studying the photophysical properties in the solid state with respect to the obtained crystal structures, the observed solid-state photophysical properties were found to depend on the relative position of the pyrene chromophores. The solid-state photophysical properties can be controlled by the alkyl groups, which provide changing crystal packing. Among the pyrenes tested, 1,3,6,8-tetraethylpyrene showed the highest fluorescence quantum yield of 0.88 in the solid state.

Pyrene derivatives with two types of substituents at positions 1, 3, 6, and 8 - fad or necessity?

1,3,6,8-Tetrasubstituted pyrene derivatives with two types of substituents in an asymmetry or axial symmetry pattern have been prepared and characterized. To the best of our knowledge, these compounds are compared for the first time to their analogs containing the same substituent at all four positions, which explains the need for their synthesis. We present information on the chemistry of pyrenes, which are substituted in the non-K region, to help obtain the most efficient materials. Moreover, theoretical studies were extended to analogs which contain the first type of substituent at positions 1 and 3, whereas the second type of substituent is located at positions 6 and 8, for which the synthesis is nontrivial. The obtained data show which trend these kinds of molecules will follow.

Non-K Region Disubstituted Pyrenes (1,3-, 1,6- and 1,8-) by (Hetero)Aryl Groups-Review

Disubstituted pyrenes at the non-K region by the same or different (hetero)aryl groups have proven to be an increasingly interesting area of research for scientists over the last decade due to their optical and photophysical properties. However, in this area, there is no systematization of the structures and synthesis methods nor their limitations. In this review, all approaches to the synthesis of these compounds, starting from the commercially available pyrene are described. Herein, the ways of obtaining of disubstituted intermediates based on bromination and acylation reaction are presented. This is crucial in the determination of the possibility of further functionalization by using coupling, cycloaddition, condensation, etc. reactions. Moreover, the application of disubstituted pyrenes in the synthesis of 1,3,6,8-tetrasubstituted was also reviewed. This review describes the directions of research on chemistry of disubstituted pyrenes.

Synthesis and Optical Properties of Donor-Acceptor-Type 1,3,5,9-Tetraarylpyrenes: Controlling Intramolecular Charge-Transfer Pathways by the Change of π-Conjugation Directions for Emission Color Modulations

In dipolar organic π-conjugated molecules, variable photophysical properties can be realized through efficient excited-state intramolecular charge transfer (ICT), which essentially depends on the π-conjugation patterns. Herein, we report a controllable regioselective strategy for synthesis and optical properties of two donor-acceptor (DA)-type 1,3,5,9-tetraarylpyrenes (i.e., 1,3-A/5,9-D (4b) and 1,3-D/5,9-A (4c)) by covalently integrating two phenyl rings and two p-OMe/CHO-substituted phenyl units into the 2-tert-butylpyrene building block, in which the two phenyl rings substituted at the 1,3-positions act as acceptors for 4b or as donors for 4c and the two p-OMe or p-CHO-substituted phenyl moieties substituted at the K-region of 5,9-positions act as donors for 4b or as acceptors for 4c, respectively. Density functional theory calculations on their frontier molecular orbitals and UV-vis absorption of S₀ → S₁ transition theoretically predicted that the change of π-conjugation directions in the two DA pyrenes could be realized through a variety of substitution patterns, implying that the dissimilar ground-state and excited-state electronic structures exist in each molecule. Their single-crystal X-ray analysis reveal their highly twisted conformations that are beneficial for inhibiting the π-aggregations, which are strikingly different from the normal 1,3,5,9-tetraphenylpyrenes (4a) and related 1,3,6,8-tetraarylpyrenes. Indeed, experimental investigations on their optical properties demonstrated that the excited-state ICT pathways can be successfully controlled by the change of π-conjugation directions through the variety of substitution positions, resulting in the modulations of emission color from deep-blue to green in solution. Moreover, for the present DA pyrenes, highly fluorescent emissions with moderate-to-high quantum yields both in the thin film and in the doped poly(methyl methacrylate) film were obtained, suggesting them as promising emitting materials for the fabrication of organic light-emitting diodes.

Synchronized Offset Stacking: A Concept for Growing Large-Domain and Highly Crystalline 2D Covalent Organic Frameworks

Covalent organic frameworks (COFs), formed by reversible condensation of rigid organic building blocks, are crystalline and porous materials of great potential for catalysis and organic electronics. Particularly with a view of organic electronics, achieving a maximum degree of crystallinity and large domain sizes while allowing for a tightly π-stacked topology would be highly desirable. We present a design concept that uses the 3D geometry of the building blocks to generate a lattice of uniquely defined docking sites for the attachment of consecutive layers, thus allowing us to achieve a greatly improved degree of order within a given average number of attachment and detachment cycles during COF growth. Synchronization of the molecular geometry across several hundred nanometers promotes the growth of highly crystalline frameworks with unprecedented domain sizes. Spectroscopic data indicate considerable delocalization of excitations along the π-stacked columns and the feasibility of donor–acceptor excitations across the imine bonds. The frameworks developed in this study can serve as a blueprint for the design of a broad range of tailor-made 2D COFs with extended π-conjugated building blocks for applications in photocatalysis and optoelectronics.

Platform Synthetic Lectins for Divalent Carbohydrate Recognition in Water

Biomimetic carbohydrate receptors ("synthetic lectins") have potential as agents for biological research and medicine. However, although effective strategies are available for "all-equatorial" carbohydrates (glucose, etc.), the recognition of other types of saccharide under natural (aqueous) conditions is less well developed. Herein we report a new approach based on a pyrene platform with polar arches extending from aryl substituents. The receptors are compatible with axially substituted carbohydrates, and also feature two identical binding sites, thus mimicking the multivalency observed for natural lectins. A variant with negative charges forms 1:2 host/guest complexes with aminosugars, with K1 >3000 m(-1) for axially substituted mannosamine, whereas a positively charged version binds the important α-sialyl unit with K1 ≈1300 m(-1) .

Functionalization of Pyrene To Prepare Luminescent Materials-Typical Examples of Synthetic Methodology

Pyrene-based π-conjugated materials are considered to be an ideal organic electro-luminescence material for application in semiconductor devices, such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaics (OPVs), and so forth. However, the great drawback of employing pyrene as an organic luminescence material is the formation of excimer emission, which quenches the efficiency at high concentration or in the solid-state. Thus, in order to obtain highly efficient optical devices, scientists have devoted much effort to tuning the structure of pyrene derivatives in order to realize exploitable properties by employing two strategies, 1) introducing a variety of moieties at the pyrene core, and 2) exploring effective and convenient synthetic strategies to functionalize the pyrene core. Over the past decades, our group has mainly focused on synthetic methodologies for functionalization of the pyrene core; we have found that formylation/acetylation or bromination of pyrene can selectly lead to functionalization at K-region by Lewis acid catalysis. Herein, this Minireview highlights the direct synthetic approaches (such as formylation, bromination, oxidation, and de-tert-butylation reactions, etc.) to functionalize the pyrene in order to advance research on luminescent materials for organic electronic applications. Further, this article demonstrates that the future direction of pyrene chemistry is asymmetric functionalization of pyrene for organic semiconductor applications and highlights some of the classical asymmetric pyrenes, as well as the latest breakthroughs. In addition, the photophysical properties of pyrene-based molecules are briefly reviewed. To give a current overview of the development of pyrene chemistry, the review selectively covers some of the latest reports and concepts from the period covering late 2011 to the present day.