Supramolecular assembly of platinum-containing polyhedral oligomeric silsesquioxanes: an interplay of intermolecular interactions and a correlation between structural modifications and morphological transformations.

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 1H NMR spectroscopy, electron microscopy, UV-vis absorption and emission spectroscopy.

Transformable nanostructures of platinum-containing organosilane hybrids: non-covalent self-assembly of polyhedral oligomeric silsesquioxanes assisted by Pt···Pt and π-π stacking interactions of alkynylplatinum(II) terpyridine moieties.

An alkynylplatinum(II) terpyridine complex functionalized with polyhedral oligomeric silsesquioxanes (POSS) moieties has been demonstrated to exhibit self-association behavior to give various distinguishable nanostructures with interesting morphological transformation from rings to rods in response to solvent conditions through the stabilization of Pt···Pt and π-π stacking interactions as well as hydrophobic-hydrophobic interactions. These changes can be systemically controlled by varying the solvent composition and have been studied by (1)H NMR, electron microscopy, UV-vis absorption, and emission spectroscopies.

Förster resonance energy transfer studies of luminescent gold nanoparticles functionalized with ruthenium(II) and rhenium(I) complexes: modulation via esterase hydrolysis.

A number of ruthenium(II) and rhenium(I) bipyridine complexes functionalized with lipoic acid moieties have been synthesized and characterized. Functionalization of gold nanoparticles with these chromophoric ruthenium(II) and rhenium(I) complexes has resulted in interesting supramolecular assemblies with Förster resonance energy transfer (FRET) properties that could be modulated via esterase hydrolysis. The luminescence of the metal complex chromophores was turned on upon cleavage of the ester bond linkage by esterase to reduce the efficiency of FRET quenching. The prepared nanoassembly conjugates have been characterized by transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), UV-visible spectroscopy, and emission spectroscopy. The quenching mechanism has also been studied by transient absorption and time-resolved emission decay measurements. The FRET efficiencies were found to vary with the nature of the chromophores and the length of the spacer between the donor (transition metal complexes) and the acceptor (gold nanoparticles).

Synthesis, characterization, and photophysical properties of Bodipy-spirooxazine and -spiropyran conjugates: modulation of fluorescence resonance energy transfer behavior via acidochromic and photochromic switching.

Two series of Bodipy-containing photochromic spirooxazine and spiropyran derivatives have been designed, synthesized and characterized by (1)H NMR, ESI mass spectrometry and elemental analysis. Their electrochemical and photochromic properties were investigated. The photophysical, ultrafast transient absorption, and fluorescence resonance energy transfer (FRET) properties from Bodipy (donor) to the ring-opened merocyanine (acceptor) were also studied. Upon photoexcitation, all the photochromic spirooxazine- and spiropyran-containing compounds exhibited reversible photochromism. Computational studies have been performed to provide further insights into the nature of the electronic transitions for the two classes of compounds. The rate constants and activation parameters for thermal bleaching reactions of compounds SO, SP-alkyne, 1-3, and 8-10 were determined through kinetic studies in acetonitrile. The thermal bleaching reaction rate of the spiropyran-containing compounds is found to be much slower than that of the spirooxazine-containing counterparts.

A platinum(II) terpyridine metallogel with an L-valine-modified alkynyl ligand: interplay of Pt⋠⋠⋠Pt, π-π and hydrogen-bonding interactions.

A series of platinum(II) terpyridine complexes with L-valine-modified alkynyl ligands has been synthesized. A complex with an unsubstituted terpyridine and one valine unit on the alkynyl is shown to be capable of gel formation, which is in sharp contrast to the gelation properties of the corresponding organic counterparts. Upon sol-gel transition, a drastic color change from yellow to red is observed, which is indicative of the involvement of Pt⋅⋅⋅Pt interactions. Through the concentration- and temperature-dependent UV/Vis absorption, emission, circular dichroism, and (1) H NMR studies, the contribution of hydrogen bonding, Pt⋅⋅⋅Pt and π-π stacking interactions as driving forces for gelation have been established, and the importance of maintaining a delicate balance between different intermolecular forces has also been illustrated.

Luminescent amphiphilic 2,6-bis(1,2,3-triazol-4-yl)pyridine-platinum(II) complexes: synthesis, characterization, electrochemical, photophysical, and Langmuir-Blodgett film-formation studies.

A new series of platinum(II) complexes with tridentate ligands 2,6-bis(1-alkyl-1,2,3-triazol-4-yl)pyridine and 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridine (N7R), [Pt(N7R)Cl]X (1-7) and [Pt(N7R)(CCR')]X (8-17; R=n-C4 H9 , n-C8 H17 , n-C12 H25 , n-C14 H29 , n-C18 H37 , C6 H5 , and CH2 -C6 H5 ; R'=C6 H5 , C6 H4 -CH3 -p, C6 H4 -CF3 -p, C6 H4 -N(CH3 )2 -p, and cholesteryl 2-propyn-1-yl carbonate; X=OTf(-) , PF6 (-) , and Cl(-) ), has been synthesized and characterized. Their electrochemical and photophysical properties have also been studied. Two amphiphilic platinum(II)2,6-bis(1-dodecyl-1,2,3-triazol-4-yl)pyridine complexes (3-Cl and 8) were found to form stable and reproducible Langmuir-Blodgett (LB) films at the air/water interface. These LB films were characterized by the study of their surface-pressure-molecular-area (π-A) isotherms, XRD, and IR and polarized-IR spectroscopy.

Synthesis and characterization of luminescent cyclometalated platinum(II) complexes of 1,3-bis-hetero-azolylbenzenes with tunable color for applications in organic light-emitting devices through extension of π conjugation by variation of the heteroatom.

A series of luminescent cyclometalated platinum(II) complexes of N^C^N ligands [N^C^N=2,6-bis(benzoxazol-2'-yl)benzene (bzoxb), 2,6-bis(benzothiazol-2'-yl)benzene (bzthb), and 2,6-bis(N-alkylnaphthoimidazol-2'-yl)benzene (naphimb)] has been synthesized and characterized. Two of the platinum(II) complexes have been structurally characterized by X-ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. In dichloromethane solution at room temperature, the cyclometalated N^C^N platinum(II) complexes exhibited rich luminescence with well-resolved vibronic-structured emission bands. The emission energies of the complexes are found to be closely related to the electronic properties of the N^C^N ligands. By varying the electronic properties of the cyclometalated ligands, a fine-tuning of the emission energies can be achieved, as supported by computational studies. Multilayer organic light-emitting devices have been prepared by utilizing two of these platinum(II) complexes as phosphorescent dopants, in which a saturated yellow emission with Commission International de I'Eclairage coordinates of (0.50, 0.49) was achieved.

Cholesterol-/estradiol-appended alkynylplatinum(II) complexes as supramolecular gelators: synthesis, characterization, photophysical and gelation studies.

A series of cholesterol-/estradiol-appended alkynylplatinum(II) complexes with tridentate N-donor ligands, based on 2,6-bis(1-alkylpyrazol-3-yl)pyridine, has been synthesized and characterized by (1)H NMR spectroscopy, FAB-mass spectrometry, and elemental analysis. Their photophysical properties have also been investigated. Computational studies have been performed to provide insights into the nature of the electronic transitions. Some of the complexes have been found to form stable thermo- and mechanoresponsive supramolecular gels.

Luminescent platinum(II) complexes of 1,3-bis(N-alkylbenzimidazol- 2'-yl)benzene-type ligands with potential applications in efficient organic light-emitting diodes.

A series of luminescent platinum(II) complexes of tridentate 1,3-bis(N-alkylbenzimidazol-2'-yl)benzene (bzimb) ligands has been synthesized and characterized. One of these platinum(II) complexes has been structurally characterized by X-ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. Computational studies have been performed on this class of complexes to elucidate the origin of their photophysical properties. Some of these complexes have been utilized in the fabrication of organic light-emitting diodes (OLEDs) by using either vapor deposition or spin-coating techniques. Chloroplatinum(II)-bzimb complexes that are functionalized at the 5-position of the aryl ring, [Pt(R-bzimb)Cl], not only show tunable emission color but also exhibit high current and external quantum efficiencies in OLEDs. Concentration-dependent dual-emissive behavior was observed in multilayer OLEDs upon the incorporation of pyrenyl ligand into the Pt(bzimb) system. Devices doped with low concentrations of the complexes gave rise to white-light emission, thereby representing a unique class of small-molecule, platinum(II)-based white OLEDs.

Recent advances in metallogels.

Amongst the areas of supramolecular chemistry, low molecular weight gelators (supramolecular gels) have been considered to be one of the most interesting soft and smart materials due to their ability to construct polymeric structures from small molecules through non-covalent interactions. Recently, metal centres have been incorporated into organic-based gelators that can integrate the interesting and unique properties of metal complexes into gelator molecules that can hardly be achieved by pure organic compounds. In this review, we will give a summary of the recent developments on metallogels and their interesting properties originating from the metal centres.

Functionalized BODIPY with various sensory units--a versatile colorimetric and luminescent probe for pH and ions.

A series of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives containing ion- and pH-sensory units have been successfully designed and synthesized. One of the compounds was structurally characterized by X-ray crystallography. Owing to the presence of an ICT absorption band, one of the compounds was found to show pronounced solvatochromic behavior in different organic solvents. Their emission energies in various solvents show a linear dependence on the Lippert solvent parameter. The cation-binding properties of the complexes with different metal ions (alkali metal, alkaline earth metal and transition metal ions) have been studied using UV-vis and emission spectroscopies. A 1:1 complexation to metal ions (Li(+), Na(+), Mg(2+), Ba(2+), Zn(2+), Cd(2+)) was found for the compound with one azacrown moiety in acetonitrile while another one with two azacrown moieties was shown to form 1:2 complexes with Zn(2+) and Mg(2+) cations. Their stability constants have been determined by both UV-vis and emission spectrophotometric methods. By introducing triarylborane moieties into the meso position and the 2-position of the BODIPY skeleton, different electronic absorption spectral changes together with an emission diminution were observed in response to fluoride ions. Ditopic binding study of 5, which was functionalized with both azacrown and triarylborane moieties, showed emission enhancement in the presence of Mg(2+) and F(-). These findings suggest that these BODIPY derivatives are capable of serving as versatile colorimetric and luminescence probes for pH, cations and F(-).

Structure, photophysical properties and computational study of a highly luminescent mixed-metal platinum(II)-silver(I) system. Potential building blocks for emissive supramolecular structures.

A luminescent cyclometalated platinum(II) complex has been shown to sandwich a silver ion, which demonstrates intense luminescence with appreciable photoluminescence quantum yield. Computational studies have been performed to provide insights into the nature of the photophysical properties.

Single-turn helix-coil strands stabilized by metal···metal and π-π interactions of the alkynylplatinum(II) terpyridyl moieties in meta-phenylene ethynylene foldamers.

Dinuclear alkynylplatinum(II) terpyridyl complexes with oligomeric bridge consisting of five repeating meta-phenylene ethynylene (mPE) units have been found to exhibit a strong tendency to fold back onto themselves to form short helical strands through the stabilization of Pt···Pt and π-π interactions. The steric bulk of the terpyridine ligands and the length of the oligomeric bridge have been found to affect the extent of the intramolecular Pt···Pt interaction that governs the stabilization of the short helical strand in solution. Their folding properties via Pt···Pt and π-π stacking interactions have been studied by (1)H NMR, 2D ROESY NMR, electronic absorption, and emission spectroscopies.

Supramolecular self-assembly of amphiphilic anionic platinum(II) complexes: a correlation between spectroscopic and morphological properties.

A new class of amphiphilic anionic platinum(II) bzimpy complexes has been demonstrated to show aggregation in water through Pt···Pt and π-π stacking interactions. An interesting aggregation-partial deaggregation-aggregation process and a morphological transformation from vesicles to nanofibers have been demonstrated. These changes can be systematically controlled by the variation of solvent composition and could readily be probed by UV-vis absorption, emission, NMR, transmission electron microscopy, and even with our naked eyes.

Synthesis, characterization, and the photochromic, luminescence, metallogelation and liquid-crystalline properties of multifunctional platinum(II) bipyridine complexes.

A series of multifunctional platinum(II) bipyridine complexes were designed, synthesized, and characterized by (1)H NMR, fast atom bombardment mass spectrometry (FAB-MS), and elemental analysis. Their electrochemical and photophysical properties were investigated. The photochromic properties of the spironaphthoxazine-containing complexes were also studied. Some of these complexes were shown to be capable of forming stable thermoreversible metallogels in organic solvents. In contrast to typical thermotropic organogels and metallogels, one of the complexes could form metallogels in dodecane and is very stable towards external stimuli. The photochromic activation parameters for the bleaching reaction of a representative spironaphthoxazine-containing complex in a dodecane gel were determined through kinetic studies at various temperatures. Lamellar liquid-crystalline behavior was also observed in one of the complexes, and the liquid-crystalline properties were studied by thermogravimetry analysis (TGA), polarized optical microscopy (POM), differential scanning calorimetry (DSC), variable-temperature X-ray diffraction (XRD), and variable-temperature infrared (IR) spectroscopy.

A luminescent cyclometalated platinum(II) complex and its green organic light emitting device with high device performance.

A luminescent cyclometalated platinum(II) complex has been demonstrated to show green electrophosphorescence in multilayer organic light-emitting devices (OLEDs) using a dual emissive layer with high current and external quantum efficiencies of 38.9 cd A(-1) and 11.5%, respectively.

Thermo- and acid-responsive photochromic spironaphthoxazine-containing organogelators.

A series of photochromic spironaphthoxazine derivatives has been designed, synthesized, and characterized by using (1)H NMR spectroscopy, FAB mass spectrometry, and elemental analysis. Their photophysical and photochromic behavior have been investigated. Two of the compounds (G(12)-en-SA-SO and G(16)-en-SA-SO) have been shown to be capable of forming stable thermoreversible organogels in organic solvents, tested by the "stable-to-inversion of a test tube" method. Addition of p-toluenesulfonic acid was found to induce the formation of stable organogels at concentrations below that of the critical gelation concentration (c.g.c.), with a concomitant change in color from colorless to purple. Transmission electron microscopy and scanning electron microscopy of the xerogels showed typical fibrous structures in the micrometer scale. The activation parameters for the bleaching reaction of G(8)-en-SA-SO in the solution state and G(16)-en-SA-SO in the gel state have been determined in ethanol through kinetic studies at various temperatures. The results showed that the rate of the bleaching reaction in the gel state was much slower than that in the solution state.

Luminescent alkynylplatinum(II) terpyridyl metallogels stabilized by Pt...Pt, pi-pi, and hydrophobic-hydrophobic interactions.

A series of luminescent alkynylplatinum(II) terpyridyl complexes have been synthesized and characterized by 1H NMR, IR, FAB-mass spectrometry, and elemental analysis; one of the platinum(III) complexes has also been structurally characterized by X-ray crystallography. Their electrochemical and photophysical properties have also been investigated. A majority of the complexes were able to form stable thermoreversible metallogels in organic solvents, tested by the "stable-to-inversion of a test tube" method. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of the xerogels showed typical fibrous structures on the micrometer scale. Interestingly, whereas 2-OTf, 3-OTf, and 5-PF6 formed thermotropic metallogels mainly through van der Waals' forces with different emission colors, 1-X (X = OTf, BF4, PF6, and ClO4) showed additional Pt...Pt and pi-pi interactions to stabilize the resultant metallogels and showed drastic color changes during the gel-to-sol phase transition. The metallogels of 1-X were also different colors, depending on the nature of the counter anions, which governs the degree of aggregation and the extent of Pt...Pt and pi-pi interactions involved in the gelation process. This property may be utilized to serve as an effective reporter for microenvironmental changes.

Unusual luminescence enhancement of metallogels of alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine complexes upon a gel-to-sol phase transition at elevated temperatures.

A series of alkynylplatinum(II) complexes of 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine has been synthesized and characterized by (1)H NMR, IR, FAB mass spectrometry, and elemental analysis; the photophysical properties have also been investigated. All the complexes have been shown to exhibit interesting gelation properties. Scanning electron microscopy (SEM) of the xerogels showed a network of fibrous structures, typical of morphologies of organogels/metallogels. Interestingly, two of the complexes were found to show strong luminescence enhancement upon a gel-to-sol phase transition upon increasing the temperature. This unusual behavior is rarely encountered, as it represents a sharp contrast to that exhibited by other typical thermotropic organogels and metallogels reported so far. Variable-temperature UV-vis and luminescence spectroscopies were performed to probe the gel-to-sol phase transition. Concentration-dependent, variable-temperature, and time-resolved emission studies in dilute benzene solution have also been made to provide further insights into the spectroscopic origin in the sol forms. A quantitative treatment of the system based on the Birks scheme has been performed.