Phosphorescence Energy Transfer: Ambient Afterglow Fluorescence from Water-Processable and Purely Organic Dyes via Delayed Sensitization

Ambient afterglow luminescence from metal-free organic chromophores would provide a promising alternative to the well-explored inorganic phosphors. However, the realization of air-stable and solution-processable organic afterglow systems with long-lived triplet or singlet states remains a formidable challenge. In the present study, a delayed sensitization of the singlet state of organic dyes via phosphorescence energy transfer from organic phosphors is proposed as an alternative strategy to realize “afterglow fluorescence”. This concept is demonstrated with a long-lived phosphor as the energy donor and commercially available fluorescent dyes as the energy acceptor. Triplet-to-singlet Förster-resonance energy-transfer (TS-FRET) between donor and acceptor chromophores, which are co-organized in an amorphous polymer matrix, results in tuneable yellow and red afterglow from the fluorescent acceptors. Moreover, these afterglow fluorescent hybrids are highly solution-processable and show excellent air-stability with good quantum yields.     

Phosphorescence Energy Transfer: Ambient Afterglow Fluorescence from Water‐Processable and Purely Organic Dyes via Delayed Sensitization

Ambient afterglow luminescence from metal‐free organic chromophores would provide a promising alternative to the well‐explored inorganic phosphors. However, the realization of air‐stable and solution‐processable organic afterglow systems with long‐lived triplet or singlet states remains a formidable challenge. In the present study, a delayed sensitization of the singlet state of organic dyes via phosphorescence energy transfer from organic phosphors is proposed as an alternative strategy to realize “afterglow fluorescence”. This concept is demonstrated with a long‐lived phosphor as the energy donor and commercially available fluorescent dyes as the energy acceptor. Triplet‐to‐singlet Förster‐resonance energy‐transfer (TS‐FRET) between donor and acceptor chromophores, which are co‐organized in an amorphous polymer matrix, results in tuneable yellow and red afterglow from the fluorescent acceptors. Moreover, these afterglow fluorescent hybrids are highly solution‐processable and show excellent air‐stability with good quantum yields.     

Manipulation of Triplet Excited States in Two-Component Systems for High-Performance Organic Afterglow Materials

The past several years have witnessed the tremendous development of novel chemical structures, new design strategies and intriguing applications in the field of room-temperature phosphorescence (RTP) and organic afterglow materials. This Review article focuses on recent advancements of high-performance organic afterglow materials obtained by two-component design strategies such as a dopant-matrix, donor–acceptor, sensitization, and energy-transfer strategies. Based on some cutting-edge studies, organic afterglow efficiency has been largely improved, exceeding 90 % in several cases. Organic afterglow durations reach tens of seconds in phosphorescence systems and hours in donor–acceptor systems. Organic afterglow brightness outcompetes some inorganic afterglow materials in the first several seconds after ceasing excitation source. Organic afterglow colors cover the whole visible regions and extend to near-infrared regions with respectful afterglow efficiency. On the basis of these achievements, researchers demonstrate promising applications of organic afterglow materials in diverse fields, which has also been reviewed.     

Effect of Gold(I) on the Room-Temperature Phosphorescence of Ethynylphenanthrene

The synthesis of two series of gold(I) complexes with the general formulae PR₃-Au-C≡C-phenanthrene (PR₃=PPh₃ ( 1 a / 2 a ), PMe₃ ( 1 b / 2 b ), PNaph₃ ( 1 c / 2 c )) or (diphos)(Au-C≡C-phenanthrene)₂ (diphos=1,1-bis(diphenylphosphino)methane, dppm ( 1 d / 2 d ), 1,4-bis(diphenylphosphino)butane, dppb ( 1 e / 2 e )) has been realized. The two series differ in the position of the alkynyl substituent on the phenanthrene chromophore, being at the 9-position (9-ethynylphenanthrene) for the L1 series and at the 2-position (2-ethynylphenanthrene) for the L2 series. The compounds have been fully characterized by ¹H, ³¹P NMR, and IR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction resolution in the case of compounds 1 a , 1 e , 2 a , and 2 c . The emissive properties of the uncoordinated ligands and corresponding complexes have been studied in solution and within organic matrixes of different polarity (polymethylmethacrylate and Zeonex). Room-temperature phosphorescence (RTP) is observed for all gold(I) complexes whereas only fluorescence can be detected for the pure organic chromophore. In particular, the L2 series presents better luminescent properties regarding the intensity of emission, quantum yields, and RTP effect. Additionally, although the inclusion of all the compounds in organic matrixes induces an enhancement of the observed RTP owing to the decrease in non-radiative deactivation, only the L2 series completely suppresses the fluorescence, giving rise to pure phosphorescent materials.     

Intermolecular Electronic Coupling of Organic Units for Efficient Persistent Room‐Temperature Phosphorescence

Although persistent room‐temperature phosphorescence (RTP) emission has been observed for a few pure crystalline organic molecules, there is no consistent mechanism and no universal design strategy for organic persistent RTP (pRTP) materials. A new mechanism for pRTP is presented, based on combining the advantages of different excited‐state configurations in coupled intermolecular units, which may be applicable to a wide range of organic molecules. By following this mechanism, we have developed a successful design strategy to obtain bright pRTP by utilizing a heavy halogen atom to further increase the intersystem crossing rate of the coupled units. RTP with a remarkably long lifetime of 0.28 s and a very high quantum efficiency of 5 % was thus obtained under ambient conditions. This strategy represents an important step in the understanding of organic pRTP emission.     

Boosting the Quantum Efficiency of Ultralong Organic Phosphorescence up to 52 % via Intramolecular Halogen Bonding

Ultralong organic phosphorescence (UOP) has attracted increasing attention due to its potential applications in optoelectronics, bioelectronics, and security protection. However, achieving UOP with high quantum efficiency (QE) over 20 % is still full of challenges due to intersystem crossing (ISC) and fast non‐radiative transitions in organic molecules. Here, we present a novel strategy to enhance the QE of UOP materials by modulating intramolecular halogen bonding via structural isomerism. The QE of CzS2Br reaches up to 52.10 %, which is the highest afterglow efficiency reported so far. The crucial reason for the extraordinary QE is intramolecular halogen bonding, which can not only effectively enhance ISC by promoting spin–orbit coupling, but also greatly confine motions of excited molecules to restrict non‐radiative pathways. This work provides a reasonable strategy to develop highly efficient UOP materials for practical applications.     

Extrinsic Heavy Metal Atom Effect on the Solid‐State Room Temperature Phosphorescence of Cyclic Triimidazole

Four coordination compounds [Zn₃(CH₃COO)₆(H₂O)₂](TT)₂ [Cd(H₂O)₆](ClO₄)₂(TT)₂, [Cd(H₂O)₆](BF₄)₂(TT)₂, [Zn(H₂O)₆](BF₄)₂(TT)₂ ( 1 – 4 ) accommodating the crystallization induced emissive triimidazo[1,2‐a:1′,2′‐c:1′′,2′′‐e][1,3,5]triazine ( TT ) as a guest in their crystal lattice are isolated and fully photophysically and structurally characterized. Their emission properties are compared with those of afterglow TT and interpreted taking into account the heavy atom effect and crystal packing similarities and differences. In the case of 1 , due to the closeness of the TT H‐aggregates arrangement with that of the phosphor's pure phase, the observed intensification of the phosphorescent emission at the expense of the prompt one is attributed to the extrinsic heavy atom effect of Zn. In 2 and 3 , the heavier Cd atom is responsible for a decrease in the lifetimes of the afterglow emission, despite the presence of tightly overlapped H‐dimers in the crystal structure. Finally, for 4 , isostructural with 3 , the Zn atom reveals in RTUP lifetime comparable with that of 1 .     

Metal–Organic Frameworks: From Molecules/Metal Ions to Crystals to Superstructures

Metal–organic frameworks (MOFs) are among the most attractive porous materials known today, exhibiting very high surface areas, tuneable pore sizes and shapes, adjustable surface functionality, and flexible structures. Advances in the formation of MOF crystals, and in their subsequent assembly into more complex and/or composite superstructures, should expand the scope of these materials in many applications (e.g., drug delivery, chemical sensors, selective reactors and removal devices, etc.) and facilitate their integration onto surfaces and into devices. This Concept article aims to showcase recently developed synthetic strategies to control the one‐, two‐ and three‐dimensional (1‐, 2‐ and 3D) organisation of MOF crystals.     

Cover Picture: Solid‐State Structural Characterization of Cutinase–ECE‐Pincer–Metal Hybrids (Chem. Eur. J. 17/2009)

The interfacial enzyme cutinase…? shown at the air–water interface on the cover, was site‐selectively modified with two different ECE‐pincer–metal complexes. The resulting cutinase–pincer–metal hybrids crystallized under halide‐rich conditions to give monomeric crystal structures, but also crystallized under halide‐poor conditions to form a metal‐induced dimer. See the Full Paper by R. J. M. Klein Gebbink, P. Gros, G. van Koten et al. on page 4270 ff. , for details of the chemistry and the crystal structures. Photograph: View from the island of Saba (Netherlands Antilles) taken by Birgit Wieczorek. Design: Birgit Wieczorek and Cornelis A. Kruithof.

     

From 3D to 2D Transition Metal Nitroprussides by Selective Rupture of Axial Bonds

1-methyl-2-pyrrolidone (1m2p) is a solvent with proven abilities for 2D-solid exfoliation due to its extremely high surface tension. In principle, such a feature could be used also to induce the selective breaking of certain bonds in solids to obtain new materials. Such a hypothesis is demonstrated in this study for transition metal nitroprussides, where 2D solids are obtained from 3D frameworks by selective rupture of axial bonds. This contribution discusses the mechanism involved in such molecular manufacture. The crystal structure for the formed 2D solids was solved and refined from XRD powder patterns recorded using synchrotron radiation. Mössbauer, IR and Raman spectra provided fine details on the electronic structure of the resulting new series of layered materials. The experimental information was complemented with calculations for the molecule configuration in its non-activated and activated forms. In the obtained 2D solids, neighboring layers of about 1 nm of thickness remain separated by activated 1m2p molecules. The interaction between neighboring layers is of a physical nature, without the presence of a chemical bond between them, as corresponds to a 2D material.     

综合化学实验：磁性金属有机骨架材料的合成及对铅的吸附

设计了一个综合实验——磁性金属有机骨架材料的合成及对铅的吸附。先合成四氧化三铁,再通过氨基修饰制备磁性金属有机骨架吸附材料。考察了此材料对铅的吸附性能,铅的浓度用火焰原子吸收光谱法测定。通过实验加深了学生对物理化学课程中吸附动力学等相关内容的理解,同时巩固了学生对仪器分析课程中的原子吸收光谱法的相关内容的掌握。