Electropolymerized highly photoconductive thin films of cyclopalladated and cycloplatinated complexes

Rational design of fluorescent chemosensor for Pd2+ based on the formation of cyclopalladated complex

According to the assumption that the formation of C-Pd bond becomes a cyclopalladated complex (CPC), we designed and synthesized two C-N-N pincer ligands of BODIPY appended 2,2'-bipyridine derivatives (BP and BPB). It has been confirmed that the C-Pd bond does exist and plays a crucial role in "on-off" fluorescence behavior. Based on it, a coordination-induced fluorescence quenching sensor for Pd²⁺ was constructed. The results indicated that BP possessed high sensitivity and specificity for Pd²⁺ in solution. The limit of detection (LOD) of BP is determined to be 0.97 nM within a linear range between 1.0 and 50.0 nM, meanwhile, the platinum-group ions demonstrate no interference. The bio-imaging application of BP was investigated and it exhibited a promising vitro test for fluorescent imaging of Pd²⁺ ions in MCF-7 cells. Meanwhile, BPB coated sensor label for Pd²⁺ was set up. The visible color variation was displayed under UV light with increasing concentrations of Pd²⁺. Briefly speaking, fluorescence probes of BP and BPB offer new approaches for Pd²⁺ detection in a lab and on-site test, as well as the vivo imaging. Then, with the aid of (TD)DFT calculation, the internal reason for the optical difference between the two ligands was disclosed. This concept of CPC containing a Pd-C covalent bond provides a promising perspective of coordination fluorescence sensors.

Tris(4'-Nitrobiphenyl)amine─An Octupolar Chromophore with High Two-Photon Absorption Cross-Section and Its Application for Uncaging of Calcium Ions in the Near-Infrared Region

Compounds with high two-photon absorption (2PA) performance in the near-infrared region have attracted great attention because of their application in the material and biological science. In this study, we have developed a simple and novel octupolar chromophore, tris(4'-nitrobiphenyl)amine 1, with three nitro peripheral groups attached to a triphenylamine core via biphenyl linkers. A mono-branched analogue 2 has also been prepared to investigate the effects of octupolar and dipolar systems on photophysical and 2PA behaviors. Compound 1, despite having a much simpler structure than the previous three-branched scaffolds, exhibits comparable σ₂ values, reaching 1330 GM at 730 nm and 900 GM at 820 nm in toluene. Combined with an outstanding σ₂/MW ratio (2.2 GM g^-1 mol) and a high fluorescence quantum yield (0.51), 1 displays potential as a promising two-photon (2P) probe for bioimaging. Subsequently, the ethylene glycol tetraacetic acid-substituted derivatives featuring octupolar (3 and 5) or dipolar (4 and 6) character have been synthesized and their one-photon (1P) and 2P photochemical reactions have been examined. Finally, 1P- and 2P-triggered uncaging of Ca²⁺ from these calcium chelators has been confirmed.

Photoconductive Properties and Electronic Structure in 3,5-Disubstituted 2-(2'-Pyridyl)Pyrroles Coordinated to a Pd(II) Salicylideneiminate Synthon

The synthesis and the electrochemical, photophysical, structural, and photoconductive properties of three new heteroleptic Pd(II) complexes with various 3′,5′- disubstituted-2-(2′-pyridil) pyrroles H(N^N) as coordinated ligands are reported. The coordination of the metal center was completed by a functionalized Schiff base H(O^N) used as an ancillary ligand. The [(N^N)Pd(O^N)] complexes showed highly interesting photoconductive properties which have been correlated to their electronic and molecular structures. Theoretical density functional theory (DFT) and time-dependent DFT calculations were performed, and the results were confronted with the organization in crystalline phase, allowing to point out that the photoconductive properties are mainly a consequence of an efficient intramolecular ligand-to-metal charge transfer, combined to the proximity between the central metal and the donor moieties in the solid-state molecular stacks. The reported results confirm that these new Pd(II) complexes form a novel class of organometallic photoconductors with intrinsic characteristics suitable for molecular semiconductors applications.

The first evidence of enhancement of the role of d* orbitals in improving photoconduction in crystalline Pd(II) complexes comprising 2-(2′-pyridyl)pyrroles.

Structures and esterolytic reactivity of novel binuclear copper(ii) complexes with reduced l-serine Schiff bases as mimic carboxylesterases

Three novel binuclear copper(ii) complexes with reduced l-serine Schiff bases were synthesized and their structures were analyzed with single-crystal X-ray diffraction and DFT calculations. The crystal data revealed that all of these binuclear complexes are chiral. Both 5-halogenated (bromo- and chloro-) binuclear complexes exhibit right-handed helix structural character. Interestingly, the 5-methyl-containing analogue has a two-dimensional pore structure. In this paper, the esterolysis reactivity of the as-prepared complexes shows that in the hydrolysis of p-nitrophenyl acetate (PNPA) these three complexes provide 26, 18, 40-fold rate acceleration as compared to the spontaneous hydrolysis of PNPA at pH 7.0, respectively. Under selected conditions, in excess buffered aqueous solution a rate enhancement by three orders of magnitude was observed for the catalytic hydrolysis of another carboxylic ester, p-nitrophenyl picolinate (PNPP). These complexes efficiently promoted PNPP hydrolysis in a micellar solution of cetyltrimethylammonium bromide (CTAB), giving rise to a rate enhancement in excess of four orders of magnitude, which is approximately 2.0-3.2 times higher than that in the buffer.

Photoconducting Devices with Response in the Visible-Near-Infrared Region Based on Neutral Ni Complexes of Aryl-1,2-dithiolene Ligands

Metal bis(1,2-dithiolene) complexes belonging to the class [Ni(Ar-edt)₂]^x- [Ar-edt^2- = arylethylene-1,2-dithiolate; Ar = phenyl, (1^x-), 2-naphthyl (2^x-); x = 0 and 1] were fully characterized by NMR, UV-visible-near-infrared (UV-vis-NIR), diffuse reflectance, and FT-IR spectroscopy, as well as cyclic voltammetry and single-crystal X-ray diffraction analysis. These complexes have emerged as new photoconducting materials that allowed for the development of a prototype of photodetectors with response in the vis-NIR region. The photodetecting devices showed in some cases quantum efficiencies orders of magnitude higher than those of previously reported 1,2-dithiolene systems.

Unusual Photoelectrochemical Properties of Electropolymerized Films of a Triphenylamine-Containing Organic Small Molecule

The electropolymerized films of poly(L)_n on an indium-tin oxide (ITO) electrode was prepared by anodic electrooxidation of a dichloromethane solution of a triphenylamine-carrying organic molecule L and were characterized/studied by ultraviolet-visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, electrochemical impedance spectroscopy, cyclic voltammetry, and photoelectrochemical measurements. Poly(L)_n films were found to show surface-controlled TPA^•+1/0 associated quasi-reversible redox and exceptionally high photocurrent generation properties. At a zero external bias potential and under 100 mW/cm² white light irradiation, a photoelectrochemical device composed of a poly(L)₁-modified ITO as the working electode, a platinum disk counter electrode, and saturated calomel electrode reference electrode in a 0.1 M Na₂SO₄ aqueous solution exhibited a significant cathode photocurrent density of 2.2 μA/cm², which could be switched to be anodic and outperform most previously reported molecule-based modified ITO electrodes under similar experimental conditions. The results indicate that poly(L)_n films offer a number of future perspectives ranging from organic photovoltaic to photoelectrochemical catalysis and sensing.

Electropolymerizable IrIII Complexes with β-Ketoiminate Ancillary Ligands

A series of electropolymerizable cyclometallated Ir^III complexes were synthesized and their electrochemical and photophysical properties studied. The triphenylamine electropolymerizable fragment was introduced by using triphenylamine-2-phenylpyridine and, respectively, triphenylamine-benzothiazole as cyclometalated ligands. The coordination sphere was completed by two differently substituted β-ketoiminate ligands deriving from the condensation of acetylacetone or hexafluoroacetylacetone with para-bromoaniline. The influence of the -CH₃ /-CF₃ substitution to the electrochemical and photophysical properties was investigated. Both complexes with CH₃ substituted β-ketoiminate were emissive in solution and in solid state. Highly stable films were electrodeposited onto ITO coated glass substrates. Their emission was quenched by electron trapping within the polymeric network as proven by electrochemical studies. The -CF₃ substitution of the β-ketoiminate leads instead to the quenching of the emission and inhibits electropolymerization.

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.

Anionic cyclometalated Pt(ii) and Pt(iv) complexes respectively bearing one or two 1,2-benzenedithiolate ligands

Novel anionic cyclometalated Pt(ii) square-planar complexes NBu4[(C^N)PtII(S^S)], containing 2-phenylpyridine H(PhPy), 2-(2,4-difluorophenyl)-pyridine H(F2PhPy) and benzo[h]quinoline H(Bzq), respectively, as a cyclometalated ligand and the dianionic 1,2-benzenedithiolate (Thio)2- fragment as an (S^S) ligand, were synthesised. By the simple addition of an equivalent of (Thio)2- to the NBu4[(C^N)PtII(Thio)] complexes, octahedral anionic NBu4[(C^N)PtIV(Thio)2] analogues were obtained, representing, to the best of our knowledge, the first examples of Pt(iv) anionic cyclometalated complexes. The molecular structures of the obtained complexes in the case of the NBu4[(Bzq)PtII(Thio)] and the NBu4[(Bzq)PtIV(Thio)2] complexes were confirmed by single crystal X-ray diffraction analysis. Furthermore, the electrochemical and photophysical properties of the two series of Pt(ii) and Pt(iv) newly synthesised complexes were studied and DFT and TD-DFT calculations were performed in order to comprehensively investigate the displayed behaviour. All Pt(ii) and Pt(iv) complexes show intense luminescence in the solid state, with remarkable enhancement of the emission quantum yields, proving to be excellent examples of aggregation-induced emission systems.

Anionic cyclometallated Pt(ii) square-planar complexes: new sets of highly luminescent compounds

Novel anionic Pt(ii) complexes were synthesized, displaying an outstanding enhancement of the emission efficiency in the solid state.

Near-IR Electrochromism in Electrodeposited Thin Films of Cyclometalated Complexes

Homogeneous thin films of controlled thickness obtained from cyclometalated complexes of general formula [(C(∧)N)M(O(∧)N)], where M = Pd(II) or Pt(II), H(C(∧)N) = 2-phenylpyridine and, respectively, 2-thienylpyridine and H(O(∧)N) = a triphenylamine functionalized Schiff base, have been deposited by oxidative electropolymerization. The films have been electrochemically and morphologically characterized. The metallopolymeric thin films present stable reversible redox behavior and typical cauliflower-like textures in agreement with a nucleation-growth electropolymerization mechanism. However, the film growth is greatly influenced by the nature of the metal center, with a higher tendency of the Pt complexes to promote the 3D growth. Furthermore, a complete spectroelectrochemical study has been performed on electrodeposited films showing near-IR absorption in the oxidized state, high contrast ratios (up to 65%) and low response times.

Thin Film Electrodeposition of Ir(III) Cyclometallated Complexes

Novel electropolymerizable Ir(III) cyclometallated complexes have been synthesized and characterized. In these complexes the cyclometallated ligands are either 2-phenylpyridineH(PhPy) or benzothiazole-triphenylamineH(BzTh-tpa), while the Ir(III) coordination sphere is completed by a Schiff base substituted with a triphenylamine fragment. A complete electrochemical study has been conducted on all complexes, in order to verify the feasibility of electropolymerization and to elucidate the role of the specific position of the triphenylamine moiety in the molecular structure. Homogeneous thin films of Ir(III) metallopolymers have been successfully obtained through electropolymerization process.