Stepwise Coordination Followed by Oxidation Mechanism for the Multichannel Detection of Cu²⁺ in an Aqueous Environment

The cyclometalated ruthenium–dipicolylamine (DPA) derivative <b>3</b>(PF₆) has been synthesized. In the presence of 1 equiv of Cu²⁺ in an aqueous environment, a new redox peak at −0.03 V vs Ag/AgCl appeared. This peak is assigned to the Cu^II/I process as a result of the complexation of Cu²⁺ with the DPA unit. In the presence of 2 equiv of Cu²⁺, the metal-to-ligand charge-transfer absorption of <b>3</b>(PF₆) at 516 nm significantly decreased and a new absorption peak at 750 nm appeared. Accordingly, the solution turned from purple to yellow. The new absorption at 750 nm is assigned to the ligand-to-metal charge-transfer absorption, as a result of the oxidation of the ruthenium component by Cu²⁺. These optical and electrochemical changes have not been observed in the presence of the other 13 metal ions examined. A single-crystal X-ray structure of <b>3·</b>Cu<b>·</b>CH₃CN<b>·</b>3ClO₄ has been obtained and used for the elucidation of the stepwise recognition mechanism (coordination followed by oxidation), together with the electrochemical and spectroscopic studies of the two model compounds <b>2</b>(PF₆) and <b>4</b> with only the ruthenium component or the DPA unit

H₂PO₄^–- and Solvent-Induced Polymorphism of an Amide-Functionalized [Pt(N^C^N)Cl] Complex

A simple [Pt­(N^C^N)­Cl] complex functionalized with an amide group was prepared, and its absorption and emission properties were examined in different solvents in response to various anions. On the one hand, in the presence of H₂PO₄^–, the solution of the complex shows distinct color changes in CH₃CN, together with a ratiometric emission change from a green emission band at 537 nm to a deep red emission band at 680 nm. On the other hand, two-step spectral changes were observed in response to H₂PO₄^– in CH₂Cl₂, with the green emission being attenuated first followed by the appearance of enhanced and yellow-green emissions at a lower-energy region. These recognition processes are highly selective for H₂PO₄^– against other common anions including F^–, Cl^–, Br^–, I^–, OAc^–, NO₃^–, and HSO₄^–. In addition, the platinum complex displays multistage emission polymorphism in mixed CH₃CN/H₂O solvent of various ratios. The hydrogen-bonding interaction between H₂PO₄^– and the amide unit was confirmed by NMR analysis. In the solid state, this platinum complex emits red light. However, the composite material of the platinum complex with H₂PO₄^– shows purely monomeric yellow emissions. The solid-state materials were further analyzed by single-crystal X-ray and Fourier-transform IR analysis. These studies suggest that this simple platinum complex is useful for the selective recognition of H₂PO₄^– and as solid-state emitting materials with tunable emission colors

Stabilization of a Cyclometalated Ruthenium Sensitizer on Nanocrystalline TiO₂ by an Electrodeposited Covalent Layer

A cyclometalated ruthenium sensitizer 3 containing a triphenylamine unit was synthesized and immobilized on a nanocrystalline TiO2 surface. By using oxidative electrochemical deposition, a covalent layer of a related cyclometalated ruthenium complex 2 was coupled to the top of dye 3. Electrochemical studies suggested that complex 2 was immobilized on the TiO2/3 film surface by a tetraphenylbenzidine linker to form a dimer-like structure. The immobilization of 3 and 2 was further supported by absorption spectral analysis. The resulting electrodeposited TiO2/(3+2) film displays significantly enhanced sensitizer stabilization toward basic aqueous NaOH solution with respect to the original TiO2/3 film. The dye-sensitized solar cells with the TiO2/(3+2) photoanode display a power conversion efficiency of 4.4%, which is slightly inferior to that with the TiO2/3 film (5.1%) under the same measurement conditions

H₂PO₄^–- and Solvent-Induced Polymorphism of an Amide-Functionalized [Pt(N^C^N)Cl] Complex

A simple [Pt­(N^C^N)­Cl] complex functionalized with an amide group was prepared, and its absorption and emission properties were examined in different solvents in response to various anions. On the one hand, in the presence of H₂PO₄^–, the solution of the complex shows distinct color changes in CH₃CN, together with a ratiometric emission change from a green emission band at 537 nm to a deep red emission band at 680 nm. On the other hand, two-step spectral changes were observed in response to H₂PO₄^– in CH₂Cl₂, with the green emission being attenuated first followed by the appearance of enhanced and yellow-green emissions at a lower-energy region. These recognition processes are highly selective for H₂PO₄^– against other common anions including F^–, Cl^–, Br^–, I^–, OAc^–, NO₃^–, and HSO₄^–. In addition, the platinum complex displays multistage emission polymorphism in mixed CH₃CN/H₂O solvent of various ratios. The hydrogen-bonding interaction between H₂PO₄^– and the amide unit was confirmed by NMR analysis. In the solid state, this platinum complex emits red light. However, the composite material of the platinum complex with H₂PO₄^– shows purely monomeric yellow emissions. The solid-state materials were further analyzed by single-crystal X-ray and Fourier-transform IR analysis. These studies suggest that this simple platinum complex is useful for the selective recognition of H₂PO₄^– and as solid-state emitting materials with tunable emission colors

Toward Stable and Efficient Solar Cells with Electropolymerized Films

Researches on the new generation of solar cell devices, including dye-sensitized solar cells (DSSCs), organic solar cells (OSCs), and perovskite solar cells (PSCs), have achieved great success in recent decades. Their long-term performance stabilities limit the commercial productions of these devices. Electropolymerization is a well-known film-deposition method to obtain electroactive and photoactive films with wide optoelectronic applications. The strategies of using cross-linked electropolymerized films toward developing stable and efficient solar cells are reviewed. In situ electropolymerization or postelectrodeposition on dye surfaces is demonstrated to improve the stabilities of DSSCs by suppressing the dye desorption from the substrate. The electropolymerized films of p- or n-type monomers are used as the anodic/cathodic interlayers, hole-transporting layers, or electron transporting layers in OSCs and PSCs with high efficiencies and good performance stabilities. The incorporation of electropolymerized films in solar cells will further boost the efficient utilization of solar energy

Monometallic Osmium(II) Complexes with Bis(<i>N</i>‑methyl­benzimida­zolyl)­benzene or -pyridine: A Comparison Study with Ruthenium(II) Analogues

Seven bis-tridentate osmium complexes with Mebib or Mebip (Mebib is the 2-deprotonated form of 1,3-bis­(<i>N</i>-methyl­ben­zimida­zolyl)­benzene and Mebip is bis­(<i>N</i>-methyl­ben­zimida­zolyl)­pyridine) have been prepared, and their electrochemical and spectroscopic properties are compared with ruthenium structural analogues. Among them, four complexes have the [Os­(NCN)­(NNN)]-type coordination, including [Os­(Mebib)­(Mebip)]­(PF₆)₂ (<b>1</b>(PF₆)₂), [Os­(dpb)­(Mebip)]­(PF₆) (<b>2</b>(PF₆), dpb is the 2-deprotonated form of 1,3-di­(pyrid-2-yl)­benzene), [Os­(Mebib)­(ttpy)]­(PF₆) (<b>3</b>(PF₆), ttpy = 4′-tolyl-2,2′:​6′,2″-ter­pyr­i­dine), and [Os­(dpb)­(ttpy)]­(PF₆) (<b>4</b>(PF₆)). The other three complexes are [Os­(Mebip)₂]­(PF₆)₂ (<b>5</b>(PF₆)₂), [Os­(Mebip)­(tpy)]­(PF₆)₂ (<b>6</b>(PF₆)₂, tpy = 2,2′:​6′,2″-ter­pyr­i­dine), and [Os­(ttpy)₂]­(PF₆)₂ (<b>7</b>(PF₆)₂) with the [Os­(NNN)­(NNN)]-type coordination. Single crystals of <b>2</b>(PF₆) and <b>6</b>(PF₆)₂ have been obtained, and their structures are studied by X-ray crystallographic analysis. The Os­(II/III) redox potentials of <b>1</b>(PF₆)₂ to <b>7</b>(PF₆)₂ progressively increase from +0.04, +0.23, +0.24, +0.36, +0.56, +0.79 to +0.94 V vs Ag/AgCl, which are 200–300 mV less positive relative to the Ru­(II/III) potentials of their ruthenium counterparts. The highest occupied molecular orbital energy levels of <b>1</b>⁺–<b>7</b>²⁺ are calculated to vary in a descending order. The ruthenium and osmium complexes have singlet metal-to-ligand charge-transfer (MLCT) transitions of similar energies and band shapes, while the osmium complexes display additional ³MLCT transitions in the lower-energy region. Complexes <b>6</b>(PF₆)₂ and <b>7</b>(PF₆)₂ emit weakly at 780 and 740 nm, respectively. Complex <b>1</b>(PF₆)₂ was synthesized as the oxidized Os­(III) salt because of the low Os­(II/III) potential. The transformation of <b>1</b>²⁺ to <b>1</b>⁺ by chemical reduction or electrolysis led to the emergence of the ¹MLCT transitions in the visible region

Stepwise Coordination Followed by Oxidation Mechanism for the Multichannel Detection of Cu²⁺ in an Aqueous Environment

The cyclometalated ruthenium–dipicolylamine (DPA) derivative <b>3</b>(PF₆) has been synthesized. In the presence of 1 equiv of Cu²⁺ in an aqueous environment, a new redox peak at −0.03 V vs Ag/AgCl appeared. This peak is assigned to the Cu^II/I process as a result of the complexation of Cu²⁺ with the DPA unit. In the presence of 2 equiv of Cu²⁺, the metal-to-ligand charge-transfer absorption of <b>3</b>(PF₆) at 516 nm significantly decreased and a new absorption peak at 750 nm appeared. Accordingly, the solution turned from purple to yellow. The new absorption at 750 nm is assigned to the ligand-to-metal charge-transfer absorption, as a result of the oxidation of the ruthenium component by Cu²⁺. These optical and electrochemical changes have not been observed in the presence of the other 13 metal ions examined. A single-crystal X-ray structure of <b>3·</b>Cu<b>·</b>CH₃CN<b>·</b>3ClO₄ has been obtained and used for the elucidation of the stepwise recognition mechanism (coordination followed by oxidation), together with the electrochemical and spectroscopic studies of the two model compounds <b>2</b>(PF₆) and <b>4</b> with only the ruthenium component or the DPA unit

Monometallic Osmium(II) Complexes with Bis(<i>N</i>‑methyl­benzimida­zolyl)­benzene or -pyridine: A Comparison Study with Ruthenium(II) Analogues

Seven bis-tridentate osmium complexes with Mebib or Mebip (Mebib is the 2-deprotonated form of 1,3-bis­(N-methyl­ben­zimida­zolyl)­benzene and Mebip is bis­(N-methyl­ben­zimida­zolyl)­pyridine) have been prepared, and their electrochemical and spectroscopic properties are compared with ruthenium structural analogues. Among them, four complexes have the [Os­(NCN)­(NNN)]-type coordination, including [Os­(Mebib)­(Mebip)]­(PF6)2 (1(PF6)2), [Os­(dpb)­(Mebip)]­(PF6) (2(PF6), dpb is the 2-deprotonated form of 1,3-di­(pyrid-2-yl)­benzene), [Os­(Mebib)­(ttpy)]­(PF6) (3(PF6), ttpy = 4′-tolyl-2,2′:​6′,2″-ter­pyr­i­dine), and [Os­(dpb)­(ttpy)]­(PF6) (4(PF6)). The other three complexes are [Os­(Mebip)2]­(PF6)2 (5(PF6)2), [Os­(Mebip)­(tpy)]­(PF6)2 (6(PF6)2, tpy = 2,2′:​6′,2″-ter­pyr­i­dine), and [Os­(ttpy)2]­(PF6)2 (7(PF6)2) with the [Os­(NNN)­(NNN)]-type coordination. Single crystals of 2(PF6) and 6(PF6)2 have been obtained, and their structures are studied by X-ray crystallographic analysis. The Os­(II/III) redox potentials of 1(PF6)2 to 7(PF6)2 progressively increase from +0.04, +0.23, +0.24, +0.36, +0.56, +0.79 to +0.94 V vs Ag/AgCl, which are 200–300 mV less positive relative to the Ru­(II/III) potentials of their ruthenium counterparts. The highest occupied molecular orbital energy levels of 1+–72+ are calculated to vary in a descending order. The ruthenium and osmium complexes have singlet metal-to-ligand charge-transfer (MLCT) transitions of similar energies and band shapes, while the osmium complexes display additional 3MLCT transitions in the lower-energy region. Complexes 6(PF6)2 and 7(PF6)2 emit weakly at 780 and 740 nm, respectively. Complex 1(PF6)2 was synthesized as the oxidized Os­(III) salt because of the low Os­(II/III) potential. The transformation of 12+ to 1+ by chemical reduction or electrolysis led to the emergence of the 1MLCT transitions in the visible region

Near-Infrared Electrochromism in Electropolymerized Metallopolymeric Films of a Phen-1,4-diyl-Bridged Diruthenium Complex

A phen-1,4-diyl-bridged tris-bidentate diruthenium complex 3(PF6)2, [Ru2(dpb)­(vbpy)4]­(PF6)2, has been designed and prepared, where dpb is 1,4-di­(pyrid-2-yl)­benzene and vbpy is 5-vinyl-2,2′-bipyridine. Upon reductive electropolymerization, metallopolymeric thin films of this complex have been deposited on platinum and ITO glass electrode surfaces. These films display two well-separated redox couples at +0.16 and +0.60 V versus Ag/AgCl. In the mixed-valent state, these films display intense intervalence charge transfer absorptions around 1300 nm. The electrochromic behavior at this wavelength has been examined by spectroelectrochemical measurements and double-potential-step chronoamperometry. A highest optical contrast ratio of 41% at 1300 nm with a coloration efficiency of 200 cm2/C has been achieved. The electrochromic behavior is highly dependent on the surface coverage. The highest contrast ratio was obtained with a film of 6.0 × 10–9 mol/cm2. In addition, a monoruthenium complex 2(PF6), [Ru­(dpb)­(vbpy)2]­(PF6), has been prepared and electropolymerized for a comparison study

Lamellar Assembly of Conical Molecules Possessing a Fullerene Apex in Crystals and Liquid Crystals

Shuttlecock molecules made of fullerene and five side chains that have previously been shown to self-assemble into a polar columnar structure are now made into a lamellar structure in crystals and liquid crystals. The molecular design is such that the conical molecules C60(C6H4C⋮CSiMe2nCnH2n+1)5Me form crystals when the silicon substituent is a methyl group and that they form smectic liquid crystals when one of them is a long hydrocarbon chain. The fullerene groups in each layer interact with each other very strongly, suggesting that such lamellar structures may be useful for organic electronics applications