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

Pyrene-Based Triphenylamine Light-Harvesting Materials with Related Structure-Property Relationships

In this study, a series of novel pyrene-based triphenylamine (TPA) and its derivatives (4,4'-dimethoxytriphenylamine, TPA-OMe) were synthesized from a newly developed chemical intermediate, bromopyrene. This approach provides a unique opportunity to systematically investigate the effects of the substituent number and position on their photophysical properties. The results demonstrate that the molar absorption coefficients and fluorescence quantum yields of these pyrene derivatives significantly increase with the number of TPA or TPA-OMe units, exhibiting excellent light-harvesting antenna characteristics. The introduction of TPA or TPA-OMe units at the 1,6-positions induces a blue shift in fluorescence while having minimal impact on the absorption bands in solution. Single-crystal X-ray diffraction analysis and solid-state fluorescence spectroscopy reveal that the steric hindrance effect of TPA-OMe groups suppresses complex intramolecular interactions, thereby preserving the antenna properties of these derivatives. Furthermore, concentration-dependent and time-resolved fluorescence spectra provide insights into the molecular aggregation behavior and energy transfer processes. The findings of this study offer a new molecular strategy for designing efficient artificial light-harvesting antenna systems and lay a theoretical foundation for their applications in energy conversion.

Pyrene-Based Light-Harvesting Antenna Molecules

Light-harvesting antenna systems (AS) with multiple light-absorbing chromophores play a vital role in absorbing sunlight and transferring the excitation energy to the reaction centers during the photosynthesis process. Learning from nature, a set of simple and artificial pyrene-based light-harvesting antenna systems have been designed and re-examined from the self-developing chemical intermediates, via combining the electron-donating 4,4-dimethoxy-triphenylamine moieties as the antenna for absorbing energy donors and transferring to the reaction center. These pyrene-based light-harvesting antenna systems exhibit a positive correlation between the molar absorption coefficient (ε), enhanced photoluminescence efficiency with unchanged emission peak, and two-photon absorption cross-section with an increasing number of antenna of TPA-OMe moieties in solution. Moreover, the excited-state dynamics of these AS indicated that the coexistence of the charge transfer (CT) state and charge separation (CS) state plays a significant role in affecting the emission behavior. The short-lived CS state was affected by the increased TPA-OMe moieties and low polar solvent, which can boost the CS decay to charge recombination (CR), resulting in enhanced emission. On the contrary, the long-lived CS state would overwhelm the CT state in high polar solvent or pyrene-based antenna molecules containing one or two TPA-OMe units.

Tuning Optical Properties of Organic Thin Films through Intermolecular Interactions - Fundamentals, Advances and Strategies

In applications ranging from photon-energy conversion into electrical or chemical forms (such as photovoltaics or photocatalysis) to numerous sensor technologies based on organic solids, the role of supramolecular structures and chromophore interactions is crucial. This review comprehensively examines the critical intermolecular interactions between organic dyes and their impact on optical properties. We explore the range of changes in absorption or emission properties observed in molecular aggregates compared to single molecules. Each effect is dissected to reveal its physicochemical foundations, relevance to different application domains, and documented examples from the literature that illustrate the potential modulation of absorption or emission properties by molecular and supramolecular structural adjustments. This work aims to serve as a concise guide for exploiting supramolecular phenomena in the innovation of novel optical and optoelectronic organic materials, with emphasis on strategic application and exploitation.

In Situ Anchoring Functional Molecules to Polymer Chains Through Supramolecular Interactions for a Robust and Self-Healing Multifunctional Waterborne Polyurethane

Nowadays, much attention is paid to the development of high-performance and multifunctional materials, but it is still a great challenge to obtain polymer materials with high mechanical properties, high self-healing properties, and multifunctionality in one. Herein, an innovative strategy is proposed to obtain a satisfactory waterborne polyurethane (PMWPU-Bx) by in situ anchoring 3-aminophenylboronic acid (3-APBA) in a pyrene-capped waterborne polyurethane (PMWPU) via supramolecular interactions. The multiple functional sites inherent in 3-APBA can produce supramolecular interactions with groups on PMWPU, promoting the aggregation of hard domains in the polymer network, which confers the PMWPU-Bx strength (7.9 MPa) and high modulus (243.2 MPa). Meanwhile, the dynamic natures of boronic ester bonds formed by the condensation of 3-APBA endow PMWPU-Bx with a high self-healing efficiency. Additionally, PMWPU-Bx exhibits fluorescence tunability due to the controlled π-π stacking. In this research, the strategy of anchoring functional molecules onto polymers through supramolecular interactions synchronously achieves the high performance and the multi-functionality of waterborne polyurethanes, but also broadens their potential applications in the fields of optical anticounterfeiting and encrypted information transmission.

Record-Breaking H2S Capture and ppm-Level Sensing with a Chemically Stable Porous Organic Cage

The first experimental investigation of a porous organic cage (POC) for the challenging task of H2S capture is reported. The N-containing cage molecular material, a tertiary amine POC (6FT-RCC3), demonstrates the highest H2S (hydrogen sulfide) capture (record capacity) for a porous material at room temperature and atmospheric pressure (20.6 mmol H2S g-1; 25 H2S molecules per cage) combined with excellent reversibility for at least five adsorption-desorption cycles. In situ FTIR spectroscopy, solid-state 13C, and 15N CP MAS NMR spectroscopy experiments are applied to investigate the adsorption mechanism, identifying relatively weak interactions via hydrogen bonding. In addition, the fluorescence performances of this POC material are evaluated for the detection and sensing of H2S, where a clear H2S selectivity is observed over other gases. Remarkably, the limit of detection (LOD) is calculated to be 0.13 mm (≈4.43 ppm) in a tetrahydrofuran (THF) solution of H2S.

In Situ Photogenerated Radicals of Hydroxyl Substituted Pyrene-Based Triphenylamines with Enhanced Transport and Free Doping/Post-Oxidation for Efficient Perovskite Solar Cells

The high-performance hole transporting material (HTM) is one of the most important components for the perovskite solar cells (PSCs) in promoting power conversion efficiency (PCE). However, the low conductivity of HTMs and their additional requirements for doping and post-oxidation greatly limits the device performance. In this work, three novel pyrene-based derivatives containing methoxy-substituted triphenylamines units (PyTPA, PyTPA-OH and PyTPA-2OH) are designed and synthesized, where different numbers of hydroxyl groups are connected at the 2- or 2,7-positions of the pyrene core. These hydroxyl groups at the 2- or 2,7-positions of pyrene play a significantly role to enhance the intermolecular interactions that are able to generate in situ radicals with the assistance of visible light irradiation, resulting in enhanced hole transferring ability, as well as an enhanced conductivity and suppressed recombination. These pyrene-core based HTMs exhibit excellent performance in PSCs, which possess a higher PCE than those control devices using the traditional spiro-OMeTAD as the HTM. The best performance can be found in the devices with PyTPA-2OH. It has an average PCE of 23.44% (PCEmax = 23.50%), which is the highest PCE among the reported PSCs with the pyrene-core based HTMs up to date. This research offers a novel avenue to design a dopant-free HTM by the combination of the pyrene core, methoxy triphenylamines, and hydroxy groups.

Pyrene-Based Deep-Blue Fluorophores with Narrow-Band Emission

High-efficiency narrow-band luminescent materials have attracted intense interest, resulting in their great colorimetric purity. This has led to a variety of high-tech applications in high-definition displays, spectral analysis, and biomedicine. In this study, a rigid pyrene core was employed as the molecular backbone, and four narrow-band pyrene-based blue emitters were synthesized using various synthetic methods (such as Lewis-acid catalyzed cyclization domino reactions, Pd-catalyzed coupling reactions like Suzuki-Miyaura and Sonogashira). Due to the steric effect of the hydroxy group at the 2-position, the target compounds exhibit deep blue emission (<429 nm, CIEy < 0.08) with full width at half-maximum (FWHM) less than 33 nm both in solution and when solidified. The experimental and theoretical results indicated that the substituents at the 1- and 3-positions afford a large dihedral angle with the pyrene core, and the molecular motion is almost fixed by multiple intra- and intermolecular hydrogen bonding interactions in the crystallized state, leading to a suppression of the vibrational relaxation of the molecular structure. Moreover, we observed that the suppression of the vibrational relaxation in the molecular structures and the construction of rigid conjugated structures can help develop narrow-band organic light-emitting materials.

Influence of Steric Effects on the Emission Behavior of Pyrene-Based Blue Luminogens

Pyrene-based derivatives have been widely deployed in organic luminescent materials because of their bright fluorescence, high charge carrier mobility, and facile modification. Nevertheless, the fluorescence output of conventional pyrenes is prone to quenching upon aggregation due to extensive intermolecular π-π stacking interactions. To address this issue, a set of new Y-shaped pyrene-containing luminogens are synthesized from a new bromopyrene chemical precursor, 2-hydroxyl-7-tert-butyl-1,3-bromopyrene, where the bromo and hydroxyl groups at the pyrene core can be readily modified to obtain the target products and provide great flexibility in tuning the photophysical performances. When the hydroxy group at the 2-position of pyrene was replaced by a benzyl group, the steric hindrance of the benzyl group not only efficiently inhibits the detrimental intermolecular π-π stacking interactions but also rigidifies the molecular conformation, resulting in a narrow-band blue emission. Moreover, the TPE-containing compounds 2c and 3c possessed characteristic aggregation-induced emission (AIE) properties with fluorescence quantum yields of up to 66% and 38% in the solid state, respectively. Thus, this article has methodically investigated the factors influencing the optical behavior, such as intermolecular interactions, and the steric effects of the substituent group, thereby opening up the potential to develop narrow-band pyrene-based blue emitters for OLED device applications.

Pyrene-Based Cationic Fluorophores with High Affinity for BF4-, PF6-, and ClO4- Anions: Detection and Removal

Anions play an indispensable role in the balance and regulation of the ecological environment and human health; however, excess anions can cause serious ecological and environment problems. Therefore, the detection and removal of excess anions in aqueous solution is not only a technological problem but also crucial for environmental protection. Herein, a set of water-soluble pyrene-based cationic fluorophores were synthesized, which exhibit high sensitivity for the detection of the anions BF4-, PF6-, and ClO4- via electrostatic interactions. Such fluorescent probes exhibit "turn-on" emission characteristics even at low concentrations of anions due to anion-π+ interactions. Moreover, these fluorescence probes act as efficient precipitating agents for the removal of the BF4-, PF6-, and ClO4- anions from an aqueous environment. This work opens up new avenues for future research on pyrene-based fluorophores as turn-on fluorescence probes for anion detection and as excellent precipitating agents in environmental settings.

Aggregation behaviour of pyrene-based luminescent materials, from molecular design and optical properties to application

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

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.

Structure-controlled intramolecular charge transfer in asymmetric pyrene-based luminogens: synthesis, characterization and optical properties

Four asymmetric D–A type pyrene-based luminogens with tunable optical properties were synthesized, which provide an efficient strategy to achieve pyrene-based full-color photoelectric materials.