A series of novel benzobphosphole alkynylgold(I) complexes has been demonstrated to display photochromic and mechanochromic properties upon applying the respective stimuli of light and mechanical ...force. Promising multistimuli‐responsive properties of this series of gold(I) complexes have been successfully achieved through judicious molecular design, which involves incorporation of the photochromic dithienylethene‐containing benzobphosphole into the triphenylamine‐containing arylethynyl ligand that is susceptible to mechanical force‐induced color changes via gold(I) complexation. With excellent thermal irreversibility and robust fatigue resistance of this series of gold(I) complexes, multicolor states controlled by the photochromism and mechanochromism have been realized. Repeatable photochromic and mechanochromic cycles without apparent loss of reactivity have also been observed under ambient conditions. The present work provides important insight and an alternative strategy for the molecular design of multistimuli‐responsive materials, paving the way for further development of the underexplored photoresponsive gold(I) complexes and the multistate photocontrolled system.
Gold complexes: Multistimuli‐responsive benzobphosphole alkynylgold(I) complexes have been prepared. The complexes display photochromism and mechanochromism. In addition, robust fatigue resistance and excellent thermal irreversibility of the photoresponsive gold(I) complexes have been realized.
Conspectus Photochromic compounds are well-known for their promising applications in many areas. In this context, many different photochromic families have been developed. As the early study of these ...photochromic compounds was mainly focused on the organic system, their photochromic reactivity was mainly derived from the singlet excited state. We hypothesized that the incorporation of the photochromic ligand to the transition metal complex and coordination complex systems would not only render the triplet state of the organic photochromic system more readily accessible due to the large spin–orbit coupling of the heavy metal center but also would lead to ready extension of the excitation wavelength to less destructive longer wavelength low-energy excitation. On the other hand, the long-lived triplet excited states of the metal complexes are also suitable for energy or electron transfer processes, which should lead to new photochromic behavior and photoswitchable functional properties. Through the incorporation of the stilbene-, azo-, spirooxazine-, and dithienylethene-containing ligands to transition metal complex systems with heavy metal centers and suitable excited states, triplet state photosensitized photochromism has been achieved. With the triplet state photosensitization, the photochromism of these compounds could be extended from the high energy UV region to the visible region. In the development of dithienylethene-containing ligands, we have adopted an alternative strategy, which involves the incorporation of nitrogen and sulfur heterocycles that directly form part of the dithienylethene framework as ligands to exert a much stronger perturbation and influence on the excited state properties of the photochromic unit by the metal center. On the basis of the new design, wide ranges of dithienylethene-containing ligands, including phenanthrolines, 2-pyridylimidazoles, N-pyridylimidazol-2-ylidenes, cyclometalating thienylpyridines, β-diketonates, and β-ketoiminates have been designed and incorporated into various coordination systems. Apart from the photosensitization, tuning of the closed form absorption and photochromic behavior based on the perturbation of the metal center, coordination-assisted planarization, modification of the ancillary ligands and introduction of various electronic excited states derived from the coordination system have been successfully demonstrated. This strategy can be used for developing NIR photochromic dithienylethenes. With the above effects observed upon the coordination to different transition metal centers and central atoms, this strategy offers a simple and effective way for the modification of the photochromic characteristics. Moreover, the emission and other functional properties of the coordination systems could also be photoswitched by the photochromic reactions.
A new class of four‐coordinate donor‐acceptor fluoroboron‐containing thermally activated delayed fluorescence (TADF) compounds bearing a tridentate 2,2′‐(pyridine‐2,6‐diyl)diphenolate (dppy) ligand ...has been successfully designed and synthesized. Upon varying the donor moieties from carbazole to 10H‐spiroacridine‐9,9′‐fluorene to 9,9‐dimethyl‐9,10‐dihydroacridine, these boron derivatives exhibit a wide range of emission colors spanning from blue to yellow with a large spectral shift of 2746 cm−1, with high PLQYs of up to 96 % in the doped thin film. Notably, vacuum‐deposited organic light‐emitting devices (OLEDs) made with these boron compounds demonstrate high performances with the best current efficiencies of 55.7 cd A−1, power efficiencies of 58.4 lm W−1 and external quantum efficiencies of 18.0 %. More importantly, long operational stabilities of the green‐emitting OLEDs based on 2 with half‐lifetimes of up to 12 733 hours at an initial luminance of 100 cd m−2 have been realized. This work represents for the first time the design and synthesis of tridentate dppy‐chelating four‐coordinate boron TADF compounds for long operational stabilities, suggesting great promises for the development of stable boron‐containing TADF emitters.
Fine‐tuned emission: A new class of four‐coordinate fluoroboron‐containing thermally activated delayed fluorescence (TADF) emitters bearing a tridentate 2,2′‐(pyridine‐2,6‐diyl)diphenolate (dppy) ligand has been successfully designed and synthesized. Efficient vacuum‐deposited OLEDs with high EQEs of 18.0 % and long half‐lifetimes of 12 733 hours have been achieved.
Other than traditional cation detection strategies, which are solely based on the ion-receptor complementarity, the extension of the concept of supramolecular chemistry and the mechanisms of ...irreversible analyte-specific reactions have also been integrated into the design of luminescent probes for the detection of cation in view of the exploration of highly sensitive and selective sensors. In this highlight, a versatile range of organic and organometallic architectures with cation-sensing capabilities based on the above mechanisms will be discussed.
The development of size‐selective membranes with well‐defined nanopores towards the precise separation of nanometer‐sized substances is a challenging task to achieve. Here a supramolecular membrane ...is presented that comprises a highly oriented, honeycomb‐like, 2D supramolecular polymer on a polycarbonate filter support. It enables precise size‐selective sieving of colloidal nanoparticles (NPs). Owing to the uniform parallel‐aligned nanocavities within the 2D supramolecular polymers, the composite membrane shows a high size‐selectivity with a sub‐nanometer accuracy in the cutoff size of about 4.0 nm. In principle, the species of size‐separable particles are unlimited, as demonstrated by quantum dots, noble metal, and metal oxide NPs. This supramolecular membrane combined with filtration advances the potential of NPs in terms of their monochromatic emission and size monodispersity, and also enables rapid removal of small magnetic NP adsorbents that are otherwise difficult to capture.
Sub‐nm sieving: A flexible supramolecular membrane for the sub‐nanometer sieving of nanoparticles is developed. This membrane comprises a highly oriented, honeycomb‐like, two‐dimensional supramolecular polymer with uniform nanocavities. Owing to this unique structural feature, a precise cutoff size of about 4 nm has been realized.
With the rich spectroscopic and luminescence properties associated with aurophilic Au⋯Au interactions, gold(I) complexes have provided an excellent platform for the design of luminescent ...chemosensors. This review concentrates on our recent exploration of luminescent gold(I) complexes in host–guest chemistry. Through the judicious design and choice of the functional receptor groups, specific chemosensors for cations and/or anions have been obtained. Utilization of sensing mechanisms based on the on–off switching of Au⋯Au interactions and photoinduced electron transfer (PET) has been successfully demonstrated. The two-coordinate nature of gold(I) complexes has also been utilized for the design of ditopic receptors through connecting both cation- and anion-binding sites within a single molecule.
Complexes of platinum(II) with polypyridine (that is, the multidentate ligands related to pyridine, such as bipyridine or terpyridine) have rich photophysical properties. These compounds are able to ...give different crystal forms in the solid state: this polymorphism is evident in the broad range of colors that can be observed in solid samples. Because of the square-planar coordination geometry of the metal center, Pt···Pt as well as π−π interactions between the chromophoric polypyridyl platinum(II) moieties are thought to contribute to the polymorphism. Owing to limited solubility, metal···metal interactions in platinum(II) polypyridyl systems had been mainly studied in the solid state, but our preparation of more soluble complexes has enabled detailed spectroscopic examinations in solution. In this Account, we describe our development of these alkynylplatinum(II) terpyridyl complexes and their unique spectral properties. A series of square-planar platinum(II) terpyridyl complexes with enhanced solubility due to the presence of the alkynyl group exhibited intense emission in solution. The lowest energy absorption and emission bands are suggested to originate from the dπ(Pt) → π*(terpy) metal-to-ligand charge transfer (MLCT) and π(CC−C6H4−R) → π*(terpy) ligand-to-ligand charge transfer (LLCT) transitions. In addition to polymorphism and a wide range of spectral properties, these complexes also exhibit “solvatochromism” and “solvatoluminescence”. They show remarkable color changes and luminescence enhancement when the diethyl ether content in a solvent mixture is varied, even as the concentration of the platinum(II) complex is held constant. The dramatic color changes and luminescence enhancement are tentatively suggested to originate from a metal−metal-to-ligand charge transfer (MMLCT) transition: reduced solvation (caused by an increase in the fraction of diethyl ether, which is the nonsolvating component of the liquid) is thought to increase Pt···Pt and π−π stacking interactions that arise from ground-state self-assembly or aggregate formation. The absorbance and luminescence wavelengths in these solvent-induced self-assemblies are also found to be dependent on the nature of the anions. Thus, counterions play an important role in governing the degree of self-assembly and the extent of interactions within these aggregates. Several polymers carrying multiple negatively charged functional groups (under basic conditions) as well as oligonucleotides have been shown to induce the aggregation and self-assembly of the positively charged water-soluble alkynylplatinum(II) terpyridyl complexes. The driving force for the induced aggregation and self-assembly is electrostatic binding of the complex molecules to the polymer, which brings the cations into a close proximity that induces Pt···Pt and π−π interactions and gives rise to remarkable color changes and luminescence enhancement. The spectral changes are shown to be related to the properties of both the complexes and the polymers. Upon electrostatic interaction, the platinum(II) complex cations are also found to stabilize the polymers and biopolymers in a helical conformation through Pt···Pt and π−π interactions. The influence on their secondary structure is revealed by significant circular dichroism (CD) signal enhancement.
The ability to precisely control the subcellular distribution of luminous materials presents unprecedented advantages for understanding cell biology and disease therapy. We introduce a luminescence ...tool for subcellular distribution imaging and differentiation of live and dead cells, utilizing cationic organoplatinum(II) complexes that exhibit well‐defined monomeric to aggregate nanostructures along with concentration‐dependent switchable luminescence from green to red due to assembly via PtII⋅⋅⋅PtII and π–π stacking interactions. One of the complexes was chosen to demonstrate the unique lysosome‐to‐nucleus subcellular re‐distribution and imaging capability in live and dead cells, respectively, which represents the first example to discriminate the subcellular localization of platinum(II) complexes through differential luminescence response. These new findings facilitate the fundamental understanding of self‐assembly behaviors of platinum(II) complexes for potential subcellular detection assays.
The aggregation affinities of the platinum(II) complexes enable them to exhibit well‐defined monomeric to aggregate nanostructures along with concentration‐dependent switchable luminescence from green to red, attributed to the extent of PtII⋅⋅⋅PtII and π–π stacking interactions. The platinum(II) complex is applied to manifest the unique lysosome‐to‐nucleus subcellular re‐distribution and imaging capability in live and dead cells.
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