Photoresponsive Dithienylethene-Containing Tris(8-hydroxyquinolinato)aluminum(III) Complexes with Photocontrollable Electron-Transporting Properties for Solution-Processable Optical and Organic Resistive Memory Devices.

The rational design of a new class of photoresponsive tris(8-hydroxyquinolinato)aluminum(III) (Alq3) complexes has been developed. By incorporating the photochromic dithienylethene units with different peripheral heterocycles into the Alq3 framework, the photochromic properties as well as photoswitching efficiency can be readily modulated, through effective photocyclization of the Al(III) complex. Such intrinsic photochromic behavior leads to the unprecedented enhancement in the electron-transporting properties as demonstrated by the as-fabricated electron-only device, rendering the realization of photoswitchable electron mobility. In addition, one of these complexes is capable of serving as an active layer for solution-processable resistive memory devices. Photocontrollable memory performance has been achieved with a binary memory behavior, with high ON/OFF ratio and long retention time. This work represents not only the first example of photoresponsive Alq3-based electron-transporting materials but also the solution-processable Alq3-based optical and resistive memory devices with photocontrollable performance.

Adaptive Coordination-Driven Supramolecular Syntheses toward New Polymetallic Cu(I) Luminescent Assemblies.

A thermally activated delayed fluorescence (TADF) tetrametallic Cu(I) metallacycle A behaves as a conformationally adaptive preorganized precursor to afford, through straightforward and rational coordination-driven supramolecular processes, a variety of room-temperature solid-state luminescent polymetallic assemblies. Reacting various cyano-based building blocks with A, a homometallic Cu(I) 1D-helical coordination polymer C and Cu8M discrete circular heterobimetallic assemblies DM (M = Ni, Pd, Pt) are obtained. Their luminescence behaviors are studied, revealing notably the crucial impact of the spin-orbit coupling offered by the central M metal center on the photophysical properties of the heterobimetallic DM derivatives.

Supramolecular Assembly of Phosphole Oxide Based Alkynylplatinum(II) 2,6-Bis(N-alkylbenzimidazol-2'-yl)pyridine Complexes-An Interplay of Hydrophobicity and Aromatic π-Surfaces.

A new class of phosphole oxide based alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine (bzimpy) complexes were synthesized and characterized. Their self-assembly was driven by hydrophobic-hydrophobic and π-π stacking interactions. The self-assembly properties were also investigated by UV/Vis absorption spectroscopy, which revealed that the alkyl-chain length of the bzimpy moiety and the π-surface area of the alkynyl ligand have significant influence on the overall self-assembly process. The alkyl-chain length also affected the morphological structures of the aggregates, which were studied by transmission electron microscopy and scanning electron microscopy.

Solvent-Induced and Temperature-Promoted Aggregation of Bipyridine Platinum(II) Triangular Metallacycles and Their Near-Infrared Emissive Behaviors.

A series of bipyridine platinum(II) complexes with different sizes of triangular metallacycles and alkyl/oligoether chains has been synthesized and characterized. They are packed in a zig-zag fashion with the formation of dimeric structures according to their X-ray crystal structures. Different emission origins are observed due to the different sizes of the triangular ligands. Their morphologies could be tuned by the modification of the molecular structures with different metallacyclic alkynyl ligands and alkyl/oligoether chains and solvents. More interestingly, unusual electronic absorption changes and upfield shifts of the aromatic proton resonances are observed upon increasing the temperature, suggesting further aggregation of the architectures. Near-infrared (NIR) emission is also realized through the tuning of the π-π stacking, Pt⋅⋅⋅Pt interactions, and the packing of planar metallacycles.

Supramolecular Self-Assembly and Dual-Switch Vapochromic, Vapoluminescent, and Resistive Memory Behaviors of Amphiphilic Platinum(II) Complexes.

A series of amphiphilic platinum(II) complexes with tridentate N-donor ligands has been synthesized and characterized. Different supramolecular architectures are constructed using the amphiphilic molecules as the building blocks through the formation of Pt···Pt and π-π stacking interactions in aqueous media. The aggregation-deaggregation-aggregation self-assembly behavior together with obvious spectroscopic changes could be fine-tuned by the addition of THF in aqueous media. More interestingly, one of the complexes is found to show fast response and high selectivity toward alcohol and water vapors with good reversibility, leading to drastic color and luminescence changes, and hence unique dual switching behavior, with the water molecules readily displaced by the alcohol vapor. Rapid writing and erasure have been realized via the control of a jet or a stream of alcohol vapor flow. In addition, it has been employed as active materials in the fabrication of small-molecule solution-processable resistive memory devices, exhibiting stable and promising binary memory performance with threshold voltages of ca. 3.4 V, high ON/OFF ratios of up to 105 and long retention times of over 104 s. The vapochromic and vapoluminescent materials are demonstrated to have potential applications in chemosensing, logic gates, VOC monitoring, and memory functions.

Multi-modulation for self-assemblies of amphiphilic rigid-soft compounds through alteration of solution polarity and temperature.

A new class of small molecule-based amphiphilic carbazole-containing compounds has been designed and synthesized. Detailed analysis of the temperature- and solvent-dependent UV-vis absorption spectra has provided insights into the cooperative self-assembly mechanism of the carbazole-containing compounds. Interestingly, the prepared amphiphilic rigid-soft compounds were also found to display a lower critical solution temperature (LCST) behavior in aqueous solution, which is relatively less explored in small molecule-based materials, leading to promising candidates for the design of a new class of thermo-responsive materials.

A Phosphole Oxide-Containing Organogold(III) Complex for Solution-Processable Resistive Memory Devices with Ternary Memory Performances.

A novel class of luminescent phosphole oxide-containing alkynylgold(III) complex has been synthesized, characterized, and applied as active material in the fabrication of solution-processable resistive memory devices. Incorporation of the phosphole oxide moiety in gold(III) system has been demonstrated to provide an extra charge-trapping site, giving rise to intriguing ternary memory performances with distinct and low switching threshold voltages, high OFF/ON1/ON2 current ratio of 1/10(3)/10(7), and long retention time for the three states. The present study offers vital insights for the future development of multilevel memory devices using small-molecule organometallic compounds.

From spherical to leaf-like morphologies: tunable supramolecular assembly of alkynylgold(I) complexes through variations of the alkyl chain length.

A series of luminescent polynuclear alkynylgold(I) complexes with different lengths of alkyl chains attached at the N-heterocyclic carbene moieties has been synthesised and demonstrated to display intriguing self-assembly behaviours through a cooperative growth mechanism. Variation of the alkyl chain length was found to cause drastic morphological differences in the aggregates and to strongly affect the thermodynamic parameters as revealed by the nucleation-elongation model.

Photo-modulated supramolecular self-assembly of ortho-nitrobenzyl ester-based alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine complexes.

The enhanced supramolecular self-assembly behaviors of photo-caged platinum(II) complexes have been triggered by applying light as the external stimulus. Distinct morphological transformation of the nanoaggregates has been observed in the photo-caged complexes before and after UV irradiation.

Cyclometalated Platinum(II) Complexes with Donor-Acceptor-Containing Bidentate Ligands and Their Application Studies as Organic Resistive Memories.

A series of heteroleptic cyclometalated platinum(II) complexes, [Pt(C^N)(O^O)], (1-10) with various donors and acceptors has been synthesized and characterized by 1 H NMR spectroscopy, elemental analyses, infrared spectroscopy and mass spectrometry. The X-ray structure of 2 has also been determined. The electrochemical and photophysical properties of the platinum(II) complexes were studied. These experimental results have been supported by computational studies. Furthermore, two of the complexes have been employed as the active material in the fabrication of resistive memory devices, exhibiting stable binary memory performance with low operating voltage, high ON/OFF ratio and long retention time.

Boron(iii) ß-diketonate-based small molecules for functional non-fullerene polymer solar cells and organic resistive memory devices.

A class of acceptor-donor-acceptor chromophoric small-molecule non-fullerene acceptors, 1-4, with difluoroboron(iii) ß-diketonate (BF2bdk) as the electron-accepting moiety has been developed. Through the variation of the central donor unit and the modification on the peripheral substituents of the terminal BF2bdk acceptor unit, their photophysical and electrochemical properties have been systematically studied. Taking advantage of their low-lying lowest unoccupied molecular orbital energy levels (from -3.65 to -3.72 eV) and relatively high electron mobility (7.49 × 10-4 cm2 V-1 s-1), these BF2bdk-based compounds have been employed as non-fullerene acceptors in organic solar cells with maximum power conversion efficiencies of up to 4.31%. Moreover, bistable resistive memory characteristics with charge-trapping mechanisms have been demonstrated in these BF2bdk-based compounds. This work not only demonstrates for the first time the use of a boron(iii) ß-diketonate unit in constructing non-fullerene acceptors, but also provides more insights into designing organic materials with multi-functional properties.

Three-Dimensional Spirothienoquinoline-Based Small Molecules for Organic Photovoltaic and Organic Resistive Memory Applications.

A new electron-rich spirothienoquinoline unit, tBuSAF-Th, has been developed via incorporation of a thienyl unit instead of a phenyl unit into the six-membered ring of the spiroacridine (SAF) and utilized for the first time as a building block for constructing small-molecule electron donors in organic solar cells (OSCs) and as active layers in organic resistive memory devices. The resulting three-dimensional spirothienoquinoline-containing 1-4 exhibit high-lying highest occupied molecular orbital (HOMO) energy levels. By the introduction of electron-deficient benzochalcogenodiazole linkers, with the chalcogen atoms being varied from O to S and Se, a progressively lower lowest unoccupied molecular orbital (LUMO) energy level has been achieved while keeping the HOMO energy levels similar. This strategy has allowed an enhanced light-harvesting ability without compromising open-circuit voltage (Voc) in vacuum-deposited bulk heterojunction OSCs using 1-4 as donors and C70 as the acceptor. Good photovoltaic performances with power conversion efficiencies (PCEs) of up to 3.86% and high short-circuit current densities (Jsc) of up to 10.84 mA cm-2 have been achieved. In addition, organic resistive memory devices fabricated with these donor-acceptor small molecules exhibit binary logic memory behaviors with long retention times and high on/off current ratios. This work indicates that the spirothienoquinoline moiety is a potential building block for constructing multifunctional organic electronic materials.

Amphiphilic Carbazole-Containing Compounds with Lower Critical Solution Temperature Behavior for Supramolecular Self-Assembly and Solution-Processable Resistive Memories.

The self-organization and resistive memory performances of a series of newly synthesized water-soluble amphiphilic carbazole derivatives have been explored. Temperature-dependent UV/Vis absorption spectroscopy has been conducted to study the isodesmic self-assembly mechanism of the carbazole-containing compounds. This class of compounds also exhibits interesting lower critical solution temperature properties, which are sensitive to concentration and ionic additives. One of the compounds has been solution-processed and utilized as an active material in the engineering of resistive memory devices, exhibiting a switching voltage of about 3.9 V, a constant ON/OFF current ratio of 106 , and a long retention time of 104  s. The present work demonstrates the versatile potential applications of water-soluble amphiphilic carbazole-containing compounds in supramolecular chemistry and resistive memory devices.

Triindole-Tris-Alkynyl-Bridged Trinuclear Gold(I) Complexes for Cooperative Supramolecular Self-Assembly and Small-Molecule Solution-Processable Resistive Memories.

A novel class of luminescent trinuclear alkynylgold(I) complexes with N-alkyl substituted triindole ligands has been synthesized and characterized. They are found to exhibit rich photophysical and electrochemical properties. The complexes have been demonstrated to display interesting supramolecular assembly with spherical nanostructures in aqueous THF solution through a cooperative growth mechanism. The self-assembly process is shown to be mediated by the π-π stacking interactions and hydrophobic-hydrophobic interactions of the triindole moieties upon solvent modulation. These gold(I) complexes have been employed as active materials in the fabrication of solution-processable resistive memory devices, showing promising binary memory performances with low switching threshold voltages of ca. 1.5 V, high ON/OFF current ratio of up to 105, long retention time of over 104 s, and excellent stability. The present work opens up a new avenue for the future design of versatile organogold(I) complexes that could serve as multifunctional materials.

Tunable self-assembly properties of amphiphilic phosphole alkynylgold(I) complexes through variation of the extent of the aromatic π-surface at the alkynyl moieties.

A new class of amphiphilic phosphole alkynylgold(I) complexes was synthesized and was demonstrated to display sheet-like nanostructures in aqueous DMSO solution. Modulation of the extent of the aromatic π-surface at the alkynyl ligands was found to affect the self-assembly properties as well as the stability of the aggregates as revealed by the nucleation-elongation model.