Jian-Yong Hu

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.

Blue-emitting butterfly-shaped 1,3,5,9-tetraarylpyrenes: synthesis, crystal structures, and photophysical properties.

The first example of aryl-functionalized, butterfly-shaped, highly fluorescent and stable blue-emitting monomers, namely, 7-tert-butyl-1,3,5,9-tetrakis(p-R-phenyl)pyrenes, were synthesized by the Suzuki-Miyaura cross-coupling reaction from a novel bromide precursor of 1,3,5,9-tetrabromo-7-tert-butylpyrene. The crystal structures and optical and electronic properties have been investigated.

An Efficient Approach to the Synthesis of Novel Pyrene-Fused Azaacenes

An efficient synthetic approach for functionalization of both the active sites (1,3-) and the K-region (4,5,9,10-) of pyrene was accomplished by bromination and oxidation with considerable yield. These novel pyrene-fused azaacenes were thoroughly investigated by X-ray diffraction studies, electrochemistry, and DFT calculations.

Pyrene-based Y-shaped solid-state blue emitters: synthesis, characterization, and photoluminescence.

A series of pyrene-based Y-shaped blue emitters, namely, 7-tert-butyl-1,3-diarylpyrenes 4 were synthesized by the Suzuki cross-coupling reaction of 7-tert-butyl-1,3-dibromopyrene with a variety of p-substituted phenylboronic acids in good to excellent yields. These compounds were fully characterized by X-ray crystallography, UV/Vis absorption and fluorescence spectroscopy, DFT calculations, thermogravimetric analysis, and differential scanning calorimetry. Single-crystal X-ray analysis revealed that the Y-shaped arylpyrenes exhibited a low degree of π stacking owing to the steric effect of the bulky tert-butyl group in the pyrene ring at the 7-position, and thus, the intermolecular π-π interactions were effectively suppressed in the solid state. Despite the significantly twisted nonplanar structures, these molecules still displayed efficient intramolecular charge-transfer emissions with clear solvatochromic shifts on increasing solvent polarity. An intriguing fact is that all of these molecules show highly blue emissions with excellent quantum yields in the solid state. Additionally, the two compounds containing the strongest electron-accepting groups, CN (4 d) and CHO (4 f), possess high thermal stability, which, together with their excellent solid-state fluorescence efficiency, makes them promising potential blue emitters in organic light-emitting device applications.

Synthesis and photophysical properties of novel butterfly-shaped blue emitters based on pyrene

Using 1,3,5,9-tetrabromo-7-tert-butylpyrene as the bromide precursor, a series of novel butterfly-shaped 1,3,5,9-tetraaryl substituted pyrene derivatives were synthesized by the Suzuki-Miyaura cross-coupling reaction. Their thermal, photophysical, electrochemical and related properties were systematically investigated. All compounds were found to exhibit high thermal stabilities with decomposition temperatures (Td) of up to 300 °C. All compounds show highly blue fluorescence emissions in the spectral region of 412-469 nm in solution (Φf: 0.45-0.92) and 410-470 nm in the solid- state (Φf: 0.48-0.75). It is noteworthy that these butterfly-shaped pyrenes 4 possess low-lying HOMO levels ranging from -4.76 to -5.93 eV, which make them promising candidates in OLED applications.

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

This article presents a novel asymmetrical functionalization strategy for the construction of dipolar molecules via efficient regioselective functionalization along the Z-axis of pyrene at both the 1,3- and 6,8-positions. Three asymmetrically substituted 1,3-diphenyl-6,8-R-disubsituted pyrenes were fully characterized by X-ray crystallography, photophysical properties, electrochemistry, and density functional theory calculations.

Iron(III) bromide catalyzed bromination of 2-tert-butylpyrene and corresponding position-dependent aryl-functionalized pyrene derivatives

The present work probes the bromination mechanism of 2-tert-butylpyrene (1), which regioselectively affords mono-, di-, tri- and tetra-bromopyrenes, by theoretical calculation and detailed experimental methods. The bromine atom may be directed to the K-region (positions 5- and 9-) instead of the more reactive 6- and 8-positions in the presence of iron powder. In this process, FeBr3 plays a significant role to release steric hindrance or lower the activation energy of the rearrangement. The intermediate bromopyrene derivatives were isolated and confirmed by 1H NMR spectrometry, mass spectroscopy and elemental analysis. Further evidence on substitution position originated from a series of aryl substituted pyrene derivatives, which were obtained from the corresponding bromopyrenes on reaction with 4-methoxy-phenylboronic acid by a Suzuki–Miyaura cross-coupling reaction. All position-dependent aryl-functionalized pyrene derivatives are characterized by single X-ray diffraction, 1H/13C NMR, FT-IR and MS, and offered straightforward evidence to support our conclusion. Furthermore, the photophysical properties of a series of compounds were confirmed by fluorescence and absorption, as well as by fluorescence lifetime measurements.

Synthesis and conformational studies of 2,11-dithia[3]metacyclo[3](1,3)pyrenophanes: the ring current interactions derived from pyrene ring

A series of 2,11-dithia[3]metacyclo[3](1,3)pyrenophanes are obtained by the coupling reaction of the corresponding 1,3-bis(bromomethyl)pyrene and bis(sulfanylmethyl)benzenes in ethanol under the high dilution conditions. The conformational studies of dithia[3]metacyclo[3](1,3)pyrenophanes as well as the ring current interactions derived from pyrene ring are described.