Carsten von Hänisch

Cooperative light-induced molecular movements of highly ordered azobenzene self-assembled monolayers

Photochromic systems can convert light energy into mechanical energy, thus they can be used as building blocks for the fabrication of prototypes of molecular devices that are based on the photomechanical effect. Hitherto a controlled photochromic switch on surfaces has been achieved either on isolated chromophores or within assemblies of randomly arranged molecules. Here we show by scanning tunneling microscopy imaging the photochemical switching of a new terminally thiolated azobiphenyl rigid rod molecule. Interestingly, the switching of entire molecular 2D crystalline domains is observed, which is ruled by the interactions between nearest neighbors. This observation of azobenzene-based systems displaying collective switching might be of interest for applications in high-density data storage.

Charge Transport through Molecular Rods with Reduced π-Conjugation

A series of oligophenylene rods of increasing lengths is synthesized to investigate the charge-transport mechanisms. Methyl groups are attached to the phenyl rings to weaken the electronic overlap of the pi-subsystems along the molecular backbones. Out-of-plane rotation of the phenyl rings is confirmed in the solid state by means of X-ray analysis and in solution by using UV/Vis spectroscopy. The influence of the reduced pi-conjugation on the resonant charge transport is studied at the single-molecule level by using the mechanically controllable break-junction technique. Experiments are performed under ultra-high-vacuum conditions at low temperature (50 K). A linear increase of the conductance gap with increasing number of phenyl rings (from 260 meV for one ring to 580 meV for four rings) is revealed. In addition, the absolute conductance of the first resonant peaks does not depend on the length of the molecular wire. Resonant transport through the first molecular orbital is found to be dominated by charge-carrier injection into the molecule, rather than by the intrinsic resistance of the molecular wire length.

Synthesis of molecular lead-pnictogen compounds including [Pb4(SbSiiPr3)6], the first structurally characterised compound with a lead-antimony bond.

The first structurally characterised lead(II) antimony compound with a chemical bond between lead and antimony, [Pb(4)(SbSiiPr(3))(6)] (3), was obtained by the reaction of iPr(3)SiSb-(SiMe(3))(2) with PbCl(2) in Et(2)O at 0 degrees C. The Pb(4)Sb(6) cage structure can be described as a Pb(4)Sb(4) heterocube where two SbSiiPr(3) edges are replaced by (SbSiiPr(3))(2). The average Pb-Sb bond length is 297.7 pm. The heterocubane compounds [PbESi-tBu(2)Ph](4) (E = P, As) were obtained from the reactions of Pb{N(SiMe(3))(2)}(2) with tBu(2)PhSiEH(2).

Cyclic and Polycyclic Gallium-Antimony Compounds: Synthesis and Crystal Structures of [GaCl(PnPr2Ph)(SbSiiPr3)]2 and [(GaCl)4(SbSiiPr3)4(PnPr2Ph)2]

The reaction of [(DME)LiE(SiMe3)2] (E = As, Sb) with iPr3SiCl in DME yields the mixed silylated compounds iPr3SiE(SiMe3)2 (1: E = As, 2: E = Sb). Compounds 1 and 2 were characterised by multinuclear NMR spectroscopy and mass spectrometry. The antimony compound 2 reacts with [GaCl3PnPr2Ph] to give the cyclic compound [GaCl(PnPr2Ph)(SbSiiPr3)]2 (3). The polycyclic Ga-Sb compound [(GaCl)4(SbSiiPr3)4(PnPr2Ph)2] (4) can be obtained from a solution of 3 in benzene. The central structural motif of 3 is a folded Ga2Sb2 four-membered ring. Compound 4 consists of a ladder-like Ga4Sb4 unit and is the first polycyclic Ga-Sb compound described. Compounds 3 and 4 were characterised by single crystal X-ray diffraction. The thermal decomposition of both compounds results in the formation of the binary phase GaSb.

Stable Alkali-Metal Complexes of Hybrid Disila-Crown Ethers

The complexation ability of hybrid disilane and ethylene containing crown ether ring systems was analyzed using 1,2-disila[12]crown-4 (1), 1,2-disila[15]crown-5 (2), 1,2-disila[18]crown-6 (3), and 1,2,7,8-tetrasila[12]crown-4 (7). Alkali-metal complexes (Li(+), Na(+), K(+)) were obtained and analyzed via X-ray diffraction. The complex stability of [Li(1,2-disila[12]crown-4)](+) and [Li(1,2,7,8-tetrasila[12]crown-4)](+) was determined, in relation to the lithium complex of [12]crown-4, by density functional theory (DFT) calculations employing the BP86/def2-TZVP level of theory. In solution, the exchange of lithium cations between pure [12]crown-4 and hybrid [12]crown-4 is on even terms, as has been shown from the relative binding affinity of compounds 1 and 7 by means of dynamic proton nuclear magnetic resonance (NMR) spectroscopy.

Variation of the Ultrafast Fluorescence Quenching in 2,6-Sulfanyl-Core-Substituted Naphthalenediimides by Electron Transfer

The ultrafast fluorescence quenching of 2,6-sulfanyl-core-substituted naphthalenediimides was investigated by transient spectroscopy. We find a strong dependence of the relaxation on the chemical structure of the substituent. Direct linking of an aryl rest to the sulfur atom leads to a strong red shift of the fluorescence in 1 ps and the disappearance of the emission in 5-7 ps depending on the polarity and viscosity of the solvent. This complex behavior is interpreted with the help of quantum chemical calculations. The calculations suggest that the initial relaxation corresponds to a planarization of the substituents and an associated partial electron transfer. This is followed by a twisting of the phenylsulfanyl substituents out of the molecular plane that allows a complete localization of the electron-donating orbital on the aryl group. Finally the back transfer happens in another 5-7 ps. For an additional methylene spacer group between the sulfur and the aryl, this sequence of relaxation steps is not possible and a simple exponential decay, slower by about 1 order of magnitude, is found.

STEPWISE ELIMINATION OF ETHANE TO SYNTHESISE NEW CYCLIC AND CAGE-LIKE GALLIUM-PHOSPHORUS COMPOUNDS

The reaction of GaEt3 with H2PSiMe2R (R = CMe2] initially yields the cyclic compound [(Et2Ga)2{P(H)SiMe2R}2] 1. 1 appears as a mixture of cis and trans isomers and has been characterized by 31P NMR spectroscopy, IR spectroscopy, and mass spectrometry. 1 decomposes at 180°C under elimination of ethane during 1 h to form the cage-like compound [EtGaPSiMe2R]4 (2). Central structural motif of 2 is a Ga4P4 heterocubane cage.

[In3(In2)3(PhP)4(Ph2P2)3Cl7(PEt3)3]– A New Molecular III/V Compound Featuring an Unusual 19-Atom Cage

Near C3symmetry is displayed by the 19-atom In-P polyhedron that forms the central structural unit in the title compound (see structure), which was synthesized by reaction of InCl3 with PEt3 and PhP(SiMe3)2. In addition to In–P bonds, the cage has In–In and P–P bonds. Six terminal chloro ligands and three PEt3 ligands surround the cluster core which itself encloses a central chloride anion.

Synthesis and coordination ability of a partially silicon based crown ether

The first hybrid crown ether with two adjacent disilane fragments was synthesized through reaction of O(Si2Me4Cl)2 (3) with O(C2H4OH)2. By means of DFT calculations, the complexation ability of 1,2,4,5-tetrasila[12]crown-4 (7) towards Li+ was determined to be considerably higher compared to [12]crown-4.

Intramolecular exchange interaction in twofold spin-labelled platinum complexes.

The synthesis and the crystal structures of two platinum bis-ethynyl-phenyl-nitronyl-nitroxide complexes are reported and solution EPR investigations evidenced the intramolecular exchange interaction through a diamagnetic transition metal based spacer.