Porous Supramolecular Assembly of Pentiptycene-Containing Gold(I) Complexes: Persistent Excited-State Aurophilicity and Inclusion-Induced Emission Enhancement

We report herein a porous supramolecular framework formed by a linear mononuclear Au(I) complex (1) via the tongue-and-groove-like joinery between the pentiptycene U-cavities (grooves) and the rod-shaped π-conjugated backbone and alkyl chains (tongues) with the assistance of C-H···π and aurophilic interactions. The framework contains distorted tetrahedral Au₄ units, which undergo stepwise and persistent photoinduced Au(I)-Au(I) bond shortening (excited-state aurophilicity), leading to multicolored luminescence photochromism. The one-dimensional pore channels could accommodate different solvates and guests, and the guest inclusion-induced luminescence enhancement (up to 300%) and/or vapochromism are characterized. A correlation between the aurophilic bonding and the luminescence activity is uncovered by TDDFT calculations. Isostructural derivatives 2 and 3 corroborate both the robustness of the porous supramolecular assembly and the mechanisms of the stimulation-induced luminescence properties of 1. This work demonstrates the cooperation of aurophilicity and structural porosity and adaptability in achieving novel supramolecular photochemical properties.

Significant differences between solid state and solution photochemistry and photophysics of mesogenic organometallic gold complexes

Five new gold complexes 4-ROC6H4C≡CAuN≡CC6H4-4-OR′ (R/R′ = CH3/C9H19 (C1N9 ), C15H31/C9H19 (C15N9 ), C6H13/C15H31 (C6N15 ), C9H19/C15H31 (C9N15 ), C12H25/C15H31 (C12N15 )) were synthesized and characterized (1H and 13C NMR, IR, Raman spectroscopy, and high resolution mass spectrometry). Their organized smectic phases were investigated by TGA, DSC, powder XRD, and polarized light optical microscopy, and the solids are found to have crystalline and amorphous domains. No evidence for Au•••Au interactions was observed. The steady state and time-resolved absorption and emission properties at 298 and 77 K were examined, and surprisingly, the excited lifetime of the triplet excited state in the solid state is extremely short-lived (<100 ps) in comparison with the microsecond time scale recorded for the solution and at 77 K. The photosensitization of 1O2 was observed in solution but not in the solid state. The nature of the singlet (ligand-to-ligand charge transfer) and triplet (ethynyl/intraligand ππ*) excited states were assessed using DFT and TD-DFT computations. The thermal and UV-photochemical formation of gold nanoparticles were performed in solution (slow) and in the solid state (faster). The thermally generated nanoparticles are found to be larger (2–20 nm; TEM) and exhibit well-defined shapes, whereas the photochemically generated ones are smaller (1–10 nm) and show ill-defined shapes.

Tripodal gold(i) polypyridyl complexes and their Cu+ and Zn2+ heterometallic derivatives. Effects on luminescence

Three gold(i) tripodal complexes containing the tris(2-pyridylmethyl)amine (TPA) ligand coordinated to Au-PR₃ moieties (PR₃ = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane, PTA (1), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, DAPTA (2) and triphenylphosphane (3)) were prepared together with a cage-like structure containing triphosphane 1,1,1-tris(diphenylphosphinomethyl)ethane (4). The luminescence of these complexes has been studied and they show a red shift upon the formation of heterometallic complexes by reaction with Zn(NO₃)₂, CuCl and [Cu(CH₃CN)₄]BF₄. The different coordination motifs of the Zn²⁺ and Cu⁺ heterometallic species and the resulting changes in the recorded absorption, emission and NMR spectra were analysed and supported by TD-DFT calculations.

Controlling the supramolecular polymerization of dinuclear isocyanide gold(i) arylethynylene complexes through tuning the central π-conjugated moiety

Tuning the middle chromophores of dinuclear gold(i) arylethynyl complexes has been demonstrated to exhibit a pronounced effect on the photophysical properties, self-assembly mechanisms and morphologies.

A Highly Selective and Sensitive Fluorescent Chemosensor for Detecting Al3+ Ion in Aqueous Solution and Plant Systems

The solubilized form of aluminum, Al³⁺, is present under acid soil conditions and toxic to both animals and plants. Detecting and quantifying Al³⁺ is vital for both chemistry and biology. A new Schiff-based fluorescent turn-on sensor (probe L) for the selective detection of the Al³⁺ ion was synthesized by coupling 2-hydroxy-1-naphthaldehyde and 2-aminoisoindoline-1,3-dione, and the structure was characterized by nuclear magnetic resonance spectra. The probe L exhibited an excellent selective and sensitive response to the Al³⁺ ion over other metal ions in DMSO-H₂O (1:9 v/v). Fluorescence quantification revealed that probe L was promising for the detection and accumulation of Al³⁺. Treating rice seedlings with Al³⁺ at 25–200 μM inhibited their growth. Al³⁺ treatment produced reactive oxygen species in rice roots. Practical applications of the fluorescent probe for the quantification of Al³⁺ in water samples and rice seedlings are demonstrated. Detecting the Al³⁺ ion with the probe L is easy and a potential alternative to existing analytical methods. The method can be used for detecting the Al³⁺ content of aqueous solution and plant systems. The novel fluorescent probe L has good potential for monitoring Al³⁺ content in the environment and biological systems.

Calixarene-based alkynyl-bridged gold(i) isocyanide and phosphine complexes as building motifs for the construction of chemosensors and supramolecular architectures

A calixarene-based alkynyl-bridged Au(i) isocyanide complex with a triazolyl group as a receptor site has been synthesized and demonstrated to be a selective chemosensor for Zn²⁺ based on Au(i)⋯Au(i) interactions.

Cooperative supramolecular polymerization of phosphorescent alkynyl-gold(i)–isocyanide complexes

In this work, coil–rod–coil organogold(i) complexes have been successfully assembled into supramolecular polymers with green phosphorescent emission signal.

Self-assembly of platinum(ii) 6-phenyl-2,2'-bipyridine complexes with solvato- and iono-chromic phenomena

Mono- and di-nuclear organoplatinum(ii) monomers with cyclometalated 6-phenyl-2,2'-bipyridine ligands have been successfully constructed. These systems are capable of displaying intriguing solvato- and iono-chromic phenomena by elaborately manipulating non-covalent PtPt metal-metal and π-π stacking interactions for their self-assembly processes.

Synthesis, photophysical properties and cation-binding studies of bipyridine-functionalized gold(i) complexes

A new family of Au(i) complexes equipped with bipyridine function demonstrate bright luminescence response to M(ii) cations in solution.

Luminescent Iridium(III) Chemosensor for Tandem Detection of F- and Al3

A new highly sensitive luminescent iridium(III) chemosensor, 1, was designed and synthesized for tandem detection of fluoride ions (F^-) and aluminum ions (Al³⁺). This sensor 1 exhibited obvious luminesce quenching by hydrogen bond interactions with F^-. In addition, the resulting 1-F complex can be further used to detect Al³⁺ through a luminesce enhancement. The detection limit (0.02 μM) of 1-F for Al³⁺ is far lower than the World Health Organization (7.41 μM) limit for drinking water. Importantly, chemosensor 1-F could be used to detect and quantify F^- and Al³⁺ reversibly. This sensor achieved rapid detection of two ions, which relies on only one probe.

A coumarin based Schiff base probe for selective fluorescence detection of Al3+ and its application in live cell imaging

A new coumarin based Schiff base compound, CSB-1 has been synthesized to detect metal ion based on the chelation enhanced fluorescence (CHEF). The cation binding properties of CSB-1 was thoroughly examined in UV-vis and fluorescence spectroscopy. In fluorescence spectroscopy the compound showed high selectivity toward Al³⁺ ion and the Al³⁺ can be quantified in mixed aqueous buffer solution (MeOH: 0.01M HEPES Buffer; 9:1; v/v) at pH7.4 as well as in BSA media. The fluorescence intensity of CSB-1 was enhanced by ~24 fold after addition of only five equivalents of Al³⁺. The fluorescence titration of CSB-1 with Al³⁺ in mixed aqueous buffer afforded a binding constant, K_a=(1.06±0.2)×10⁴M^-1. The colour change from light yellow to colourless and the appearance of blue fluorescence, which can be observed by the naked eye, provides a real-time method for Al³⁺ sensing. Further the live cell imaging study indicated that the detection of intracellular Al³⁺ ions are also readily possible in living cell.

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.

Cooperative self-assembly and gelation of organogold(i) complexes via hydrogen bonding and aurophilic Au⋯Au interactions

Organogold(i)-based fibers and gels have been successfully constructed, which involve Au⋯Au interactions in the self-assembled structures.

A rhodamine embedded bio-compatible smart molecule mimicking a combinatorial logic circuit and ‘key-pad lock’ memory device for defending against information risk

A rhodamine-based chemosensor LC with a colorimetric response towards Al³⁺ and Cu²⁺ and only a fluorescence response to Al³⁺ enables us to fabricate a ‘key-pad-logic’ function.

A highly sensitive fluorescent sensor for Al3+and Zn2+based on a diarylethene salicylhydrazide Schiff base derivative and its bioimaging in live cells

A new photochromic diarylethene based sensor with a salicylhydrazide Schiff base displayed a dual-mode with a “turn on” fluorescence response and color changes upon addition of Al³⁺or Zn²⁺.

Homoleptic gold(i) N-heterocyclic allenylidene complexes: excited-state properties and lyotropic chromonics

Phosphorescent Au(i) bis(N-heterocyclic allenylidene) complexes exhibit panchromatic transient absorption upon electronic photo-excitation and can self-organize into lyotropic chromonic mesophases in aqueous solutions.

A novel 8-hydroxyquinoline-pyrazole based highly sensitive and selective Al(iii) sensor in a purely aqueous medium with intracellular application: experimental and computational studies

A new 8-hydroxyquinoline-pyrazole based probe senses Al³⁺ and hence Al³⁺–8Q-NH-Pyz complex mediated F⁻ in a purely aqueous medium.

Synthesis and cation-binding studies of gold(i) complexes bearing oligoether isocyanide ligands with ester and amide as linkers

Bis(alkynyl)calix[4]arene gold(i) isocyanide complexes with amide linkers show strong binding affinity towards Al³⁺, which turns on the low-energy emission associated with the presence of Au(i)⋯Au(i) interactions.

A robust fluorescent chemosensor for aluminium ion detection based on a Schiff base ligand with an azo arm and application in a molecular logic gate

A new azo based chemosensor for detection of Al³⁺ ion has been reported. The sensor has been well characterized using different techniques like single crystal X-ray, NMR, IR, UV etc. Detection limit of the chemosensor was found to be 6.93 nM.

A long lifetime luminescent iridium(iii) complex chemosensor for the selective switch-on detection of Al3+ ions

A novel luminescent cyclometalated iridium(iii) complex 1 was synthesized and employed as a chemosensor for the detection of Al³⁺ ions. 1 displays a long lifetime luminescence that allow 1 to detect Al³⁺ ions in strong fluorescence media.

Solvent-dependent fluorescent-colorimetric probe for dual monitoring of Al3+ and Cu2+ in aqueous solution: an application to bio-imaging

A solvent-dependent reversible fluorescent-colorimetric bis-iminopyridyl Schiff base receptor (N¹E,N⁴E)-N¹,N⁴-bis(quinolin-4-ylmethylene)benzene-1,4-diamine (L) has been developed for the first time for sensitive and selective determination of Al³⁺ and Cu²⁺ in aqueous solution.

A New Fluorescence Turn-On Probe for Aluminum(III) with High Selectivity and Sensitivity, and its Application to Bioimaging

The development of novel selective probes with high sensitivity for the detection of Al(3+) is widely considered an important research goal due to the importance of such probes in medicine, living systems and the environment. Here, we describe a new fluorescent probe, N'-(4-diethylamino-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (1), for Al(3+). Probe 1 was evaluated in a solution of acetonitrile/water (1:1 v/v). Compared with previously reported probes for Al(3+), probe 1 can be synthesized easily and in high yield. A Job plot confirmed that probe 1 is able to complex Al(3+) in a 1:1 ratio, and the binding constant was determined to be 4.25×10(8) m(-1). Moreover, the detection limit was as low as 6.7×10(-9) m, suggesting that probe 1 has a high sensitivity. Common coexistent metal ions, such as K(+), Co(2+), Ca(2+), Ba(2+), Ni(2+), Pb(2+), Hg(2+), Ce(2+), Zn(2+), Cd(2+), Fe(3+), showed little or no interference in the detection of Al(3+) in solution, demonstrating the high selectivity of the probe. Finally, the ability of probe 1 to act as a fluorescent probe for Al(3+) in living systems was evaluated in Gram-negative bacteria, Escherichia coli, and confocal laser scanning microscopy confirmed its utility. The results of this study suggest that 1 has appropriate properties to be developed for application as a fluorescent probe of Al(3+) for use in biological studies.

A new pyrazoline-based fluorescent sensor for Al3+ in aqueous solution

A new pyrazoline-based fluorescent sensor was synthesized and the structure was confirmed by single crystal X-ray diffraction. The sensor responds to Al(3+) with high selectivity among a series of cations in aqueous methanol. This sensor forms a 1:1 complex with Al(3+) and displays fluorescent quenching.