Polyyne [3]rotaxanes: Synthesis via dicobalt carbonyl complexes and enhanced stability

New strategies for synthesizing polyyne polyrotaxanes are being developed as an approach to stable carbyne ‘insulated molecular wires’. Here we report an active metal template route to polyyne [3]rotaxanes, using dicobalt carbonyl masked alkyne equivalents. We synthesized two [3]rotaxanes, both with the same C28 polyyne dumbbell component, one with a phenanthroline-based macrocycle and one using a 2,6-pyridyl cycloparaphenylene nanohoop. The thermal stabilities of the two rotaxanes were compared with that of the naked polyyne dumbbell in decalin at 80 °C, and the nanohoop rotaxane was found to be 4.5 times more stable.

Dipyridylmethane Ethers as Ligands for Luminescent Ir Complexes

This work reports two new cationic heteroleptic cyclometalated iridium complexes, containing ether derivatives of di(pyridin-2-yl)methanol. The new ligands are based on dipyridin-2-ylmethane and are designed to obtain ether-based intermediates with extended electronic conjugation by insertion of π system such as phenyl, allyl and ethynyl. Different synthetic strategies were employed to introduce these units, as molecular wires, between the dipyridin-2-ylmethane chelating portion and the terminal N-containing functional group, such as amine and carbamide. The corresponding complexes show luminescence in the blue region of the spectrum, lifetimes between 0.6 and 2.1 μs, high quantum yield and good electrochemical behavior. The computational description (DFT) of the electronic structure highlights the key role of the conjugated π systems on optical and electrochemical properties of the final products.

Flipping the switch: reverse-demand voltage-sensitive fluorophores

Fluorescence microscopy with fluorescent reporters that respond to environmental cues are a powerful method for interrogating biochemistry and biophysics in living systems. Photoinduced electron transfer (PeT) is commonly used as a trigger to modulate fluorescence in response to changes in the biological environment. PeT based indicators rely either on PeT into the excited state (acceptor PeT) or out of the excited state (donor PeT). Our group has been developing voltage-sensitive fluorophores (VF dyes) that respond to changes in biological membrane potential. We hypothesize that the mechanism of voltage sensitivity arises from acceptor PeT (a-PeT) from an electron-rich aniline-containing molecular wire into the excited state fluorophore, resulting in decreased fluorescence at negative membrane potentials. Here, we can reverse the direction of electron flow to access donor-excited PeT (d-PeT) VF dyes by introducing electron-withdrawing (EWG), rather than electron-rich molecular wires. Similar to first-generation aniline containing VF dyes, EWG-containing VF dyes show voltage-sensitive fluorescence, but with the opposite polarity: hyperpolarizing membrane potentials now give fluorescence increases. We use a combination of computation and experiment to estimate a ΔE of ~0.6 eV for voltage sensitivity in d-PeT indicators, show that two of the new reverse VF dyes are voltage sensitive, and provide the first example, to our knowledge, of a molecular sensor that can be tuned across energy regimes to access bi-directional electron flow for fluorescence sensing in living systems.

One-Dimensional Bis(dipyrrinato)zinc(II)-Linked Porphyrinatozinc(II) Polymer: Synthesis, Exfoliation Into Single Wires, and Photofunctionality

One-dimensional bis(dipyrrinato)zinc(II)-linked porphyrinatozinc(II) polymer, 2 were synthesized by facile metal complexation reaction between 5,15-bis(3,5-dioctyloxyphenyl)-10,20-bis(dipyrrinato)porphyrinatozinc(II),1 and zinc(II) acetate. The bulky substituents on the porphyrin units allows 2 to be exfoliated into single molecular wires with a 2.8 nm height and 1.4 Om length. 2 exhibited promising photofunctionality derived from electronic interaction between bis(dipyrrinato)zinc and porphyrinatozinc(II) moieties, which can be engaged in energy transfer system such as photonic molecular wires.

Investigation of transport behavior in borospherene-based molecular wire for rectification applications

The transport properties of molecular wire comprising of B40 fullerene are investigated by employing density functional theory (DFT) and non-equilibrium green’s function (NEGF) methodology. The quantum transport is evaluated by calculating the density of states, transmission spectra at various bias voltages, molecular energy spectra, HOMO-LUMO gap, current–voltage curve, and transmission pathways. In context to its properties, results show that by increasing the length of molecular wire, the device exhibits rectification ratio and prominent NDR behavior. I–V curve scrutinizes that as the length of wire is increased the curve becomes non-linear. This non-linear behavior is more prominent in the case when the length of wire is increased up to six fullerene cages significant rectification ratio (R.R) and negative differential resistance (NDR) comes into the picture. The excellent negative differential resistance ensures that a device with at least six molecular wires can be used as a tunnel diode. Graphic abstract

Electronic and Magnetic Properties of One Dimensional Sandwich Transition Metal-Anthracene Molecular Wires

Organometallic sandwich complexes have been attracting tremendous interest for their potential applications in electronics and spintronics. Here, we systematically studied the structures, electronic and magnetic properties of one dimensional (1D) transition metal (TM)-anthracene (Ant) sandwich molecular wires (SMWs), [TM2Ant]∞ and [TM3Ant]∞ (TM=Ti, V, Cr, Mn), based on density functional theory calculations. Our results showed that all the 1D SMWs display normal sandwich configurations with their binding energies closely related to the choice of TM atoms. Excepting 1D [Mn2Ant]∞ and [Fe3Ant]∞ favoring antiferromagnetic ordering, most 1D [TM2Ant]∞ and [TM3Ant]∞ SMWs display robust ferromagnetic feathers. Particularly, 1D [Cr3Ant]∞ SMW is revealed to be ferromagnetic half-metal with large magnetic moment of 28.0µB per unit cell. Further spintransport calculations double proved that 1D [Cr3Ant]∞ SMW are good spintransport molecular devices. Our findings shed light on the properties of 1D Ant based SMWs and propose a new way to design potential electronic and spintronic devices.