ConspectusPhotochromic 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.

Ko Chi Chiu    任咏华    

Accounts of Chemical Research

2018

Isomeric double-decker silsesquioxane-functionalized dinuclear alkynylplatinum(ii) terpyridine complexes demonstrate self-association behaviours via the stabilisation of hydrophobic, Pt⋯Pt and/or π-π stacking interactions. These supramolecular architectures and molecular packings are found to be closely related to the isomeric configurations of the complexes and have been investigated using various spectroscopic studies.

Au-Yeung Ho-Leung    Leung Sammual Yu-Lut    任咏华    

Chemical Communications

2018

Establishment of energy landscape has emerged as an efficient pathway for improved understanding and manipulation of both thermodynamic and kinetic behaviors of complicated supramolecular systems. Herein, we report the establishment of energy landscapes of supramolecular coassembly of platinum(II) complexes and polymers, as well as the fabrication of nanostructures with enhanced complexity and intriguing properties from the coassembly systems. In the energy landscape, coassembly at room temperature has been found to only allow the longitudinal growth of platinum(II) complexes and block copolymers into core-shell nanofibers that are the kinetically trapped products. Thermal annealing can switch on the transverse growth of platinum(II) complexes and block copolymers to produce core-shell nanobelts that are the thermodynamically stable nanostructures. The extents of the transverse growth are found to increase with thermal annealing temperatures, leading to nanobelts with larger widths. Besides, rapid quenching of a hot coassembly mixture to room temperature can capture intermediate nanobelt-block-nanofiber nanostructures that are metastable and capable of converting to nanobelts upon further incubation at room temperature. Moreover, sonication treatment has been found to couple with the energy landscape of the coassembly system and open a unique energy-driven pathway to activate the kinetically forbidden nanofiber-to-nanobelt morphological transformation. Furthermore, based on the established energy landscapes, nanosphere-block-nanobelt nanostructures with distinct segmented architectures have been fabricated by thermal annealing of the ternary mixture of platinum(II) complexes, block copolymers, and polymer brushes in a one-pot and single-step procedure. Finally, the nanobelts and nanosphere-block-nanobelt nanostructures are found to possess intriguing morphological stability against acid and dilution, exhibiting characteristics that are important for promising biomedical applications.

Zhang Kaka    Yeung Margaret Ching-Lam    Leung Sammual Yu-Lut    任咏华    

Journal of the American Chemical Society

2018

A series of alkynylplatinum(II) terpyridine complexes with triethylene glycol units was synthesized, and their self-Assembly properties were investigated in solution by UV-vis absorption, emission, and 1H NMR spectroscopy. The aggregation behaviors of several water-soluble complexes were investigated in aqueous media. Some of them were found to give rise to uniform fibers, suggesting the important role that triethylene glycol units has in regulating their self-Assembly properties. Further modifications of these structures through the incorporation of alkyl chains and changes in counteranions have rendered the complexes more amphiphilic in nature, and the effect of their alkyl chain lengths was studied and optimized. The distinguishable color and spectral changes upon variations in solvent compositions might have potential applications in developing colorimetric and luminescent probes for the detection of microenvironment change. Furthermore, an optimum chain length, i.e., n-butyl chain, is required for the formation of stable and ordered nanostructures. This represents a delicate balance among Pt···Pt, φ-φ stacking, and hydrophobic-hydrophobic interactions and provides guiding principles into the construction of supramolecular materials with practical applications.

Fu Heidi Li-Ki    Po Charlotte    Leung Sammual Yu-Lut    任咏华    

ACS Applied Materials and Interfaces

2017

A series of alkynylplatinum(ii) terpyridine complexes functionalized with polyhedral oligomeric silsesquioxane (POSS) moieties has been demonstrated to exhibit drastic color changes and give various distinctive nanostructures with interesting multi-stage morphological transformations from spheres to nanoplates in response to solvent conditions through the interplay of various intermolecular interactions, including hydrophilic-hydrophilic, hydrophobic-hydrophobic, Pt⋯Pt and π-π stacking interactions. These supramolecular architectures can be systematically modified and controlled through the molecular design and the variation of solvent compositions. In particular, drastic changes in color in response to solvent polarity were observed through the incorporation of the charged moieties, representing a new class of potential candidates for functional materials with sensing or imaging capabilities. This class of complexes has been studied by H NMR spectroscopy, electron microscopy, UV-vis absorption and emission spectroscopy.

Au-Yeung Ho-Leung    Anthony yiu yan Tam    Leung Sammual Yu-Lut    任咏华    

Chemical Science

2017

A new class of highly luminescent bipolar alkynylplatinum(II) complexes has been synthesized, characterized, and applied as phosphorescent dopants in the fabrication of solution-processable organic light-emitting devices (OLEDs). Through the incorporation of a delicate balance of electron-donating carbazole moieties and electron-accepting phenylbenzimidazole or oxadiazole moieties into the platinum(II) core, the platinum(II) complexes have been demonstrated to exhibit bipolar charge transport character with high photoluminescence quantum yields of up to 0.75 in thin films. The introduction of meta-linkages into the complexes further helps weaken the donor-acceptor interactions, facilitating better carrier-transporting abilities. More importantly, high-performance solution-processable green-emitting OLEDs with maximum current efficiencies of up to 57.4 cd A and external quantum efficiencies of up to 16.0% have been realized. This is among the best performances for solution-processable phosphorescent OLEDs reported based on platinum(II) complexes as well as bipolar metal complexes.

Kong Fred Ka-Wai    Tang Man-Chung    Wong Yi-Chun    Ng Maggie    Mei yee Chan    任咏华    

Journal of the American Chemical Society

2017

A class of luminescent cyclometalated gold(III) complexes with oligo(ethylene glycol)- and poly(ethyleneoxide)-block-poly(propylene oxide)-block-poly-(ethylene oxide)-based (PEO-PPO-PEO) alkynyl ligands has been synthesized and characterized. Their photophysical and electrochemical properties have been studied. Cyclometalated gold(III) complexes with oligo(ethylene glycol)-based alkynyl ligands are found to show different aggregation morphologies in DMSO while those with PEO-PPO-PEO-based alkynyl ligand exhibited lower critical solution temperature (LCST) properties in methanol−water (1:1 v/v). Their self-assembly properties have been studied by scanning electron microscopy, transmission electron microscopy, variable-temperature H NMR and UV–vis absorption spectroscopy.

Siu Steven Kin-Lok    Chung Clive Yik-Sham    任咏华    

Journal of Organometallic Chemistry

2017

A new class of platinum(ii) terpyridine complexes with a phosphole-derived bridging alkynyl ligand have been prepared. The X-ray crystal structure of complex 2 has been determined, and reveals a polymeric zig-zag chain structure with the existence of π-π stacking interactions. The photophysical properties have also been studied, with MLCT/LLCT phosphorescence exhibited in degassed CHCl; the energy of which is varied by the π-conjugation of the terpyridine ligands. The solvent-induced assembly of complex 1 has been studied. The incorporation of hydrophobic hydrocarbon chains has been shown to play an important role in assisting the formation of self-assembled nanostructures via Pt⋯Pt, π-π stacking and hydrophobic-hydrophobic interactions. It has been established that an isodesmic growth mechanism operates in polar media to give nanospheres, while fibrous networks originate from the self-assembly of the complexes in non-polar media, predominantly driven by π-π stacking interactions.

Leung Sammual Yu-Lut    Evariste Sloane    Lescop Christophe    Hissler Muriel    任咏华    

Chemical Science

2017

A class of dithienylethene-containing boron(III) diketonates with long alkoxy chains, together with their corresponding β-diketone ligands, has been prepared and characterized. The photophysics, electrochemistry, and photochromism of the compounds have been investigated. Some of them exhibit gelation behavior, which has been explored by variable-temperature UV-vis absorption studies, and the morphology of the gels has been studied by electron microscopy. In addition, the organogels have been found to be photoresponsive with color changes under photoexcitation, leading to the construction of multiresponsive boron(III) diketonate-based materials.

Wong Cheok-Lam    Poon Chun-Ting    任咏华    

Organometallics

2017

Multi-stimuli-responsive tetranuclear gold(I) complexes were prepared based on a tetra(alkynyl)calix[4]arene framework, with incorporation of a series of isocyanide ligands of tunable hydrophilicity. This class of complex was found to exhibit high sensitivity towards group IIIA metal ions especially In. Drastic electronic absorption and emission changes were observed, which could be attributed to the formation of Au⋅⋅⋅Au interactions during the binding event. Solvent-induced self-aggregation was also observed upon changing the solvent environment to a more polar medium, with the formation of nanoaggregates and the turning-on of the aurophilic interactions, leading to interesting luminescence and morphological changes. The aggregation process was monitored by UV/Vis absorption, emission and H NMR spectroscopy and dynamic light scattering (DLS) studies, and the morphological changes were studied by electron microscopy. This new class of complex has shown high sensitivity towards external stimuli and demonstrated the feasibility of employing the on–off switching of aurophilicity as an effective design strategy for the construction of functional supramolecular systems.

Chu Anlea    Hau Franky Ka-Wah    任咏华    

Chemistry - A European Journal

2017