Clustering feature of metal atoms in pentacene molecular solids: first-principles study

Metal-atom contamination often induces the degradation of organic molecular devices. In this work, we studied clustering feature of Au and Al impurity metal atoms in pentacene solids by the first-principles calculations. We found that Au atoms prefer to produce clusters in a molecule-edge space due to the strong bonding among Au atoms, and such clusters can increase their sizes by producing molecule vacancies. On the other hand, Al atom prefers to locate separately around the center of pentacene molecules due to the strong bonding between Al atom and surrounding molecules, which produces the scattering distribution of Al atoms in pentacene solids.

A Simple Model of Ballistic Conduction in Multi-Lead Molecular Devices

A fully analytical model is presented for ballistic conduction in a multi-lead device that is based on a π-conjugated carbon framework attached to a single source lead and several sink leads. This source-and-multiple-sink potential (SMSP) model is rooted in the Ernzerhof source-and-sink potential (SSP) approach and specifies transmission in terms of combinations of structural polynomials based on the molecular graph. The simplicity of the model allows insight into many-lead devices in terms of constituent two-lead devices, description of conduction in the multi-lead device in terms of structural polynomials, molecular orbital channels, and selection rules for active and inert leads and orbitals. In the wide-band limit, transmission can be expressed entirely in terms of characteristic polynomials of vertex-deleted graphs. As limiting cases of maximum connection, complete symmetric devices (CSD) and complete bipartite symmetric devices (CBSD) are defined and solved analytically. These devices have vanishing lead-lead interference effects. Illustrative calculations of transmission curves for model small-molecule systems are presented and selection rules are identified.

Synergistic regulation of nonbinary molecular switches by protonation and light

We report a molecular switching ensemble whose states may be regulated in synergistic fashion by both protonation and photoirradiation. This allows hierarchical control in both a kinetic and thermodynamic sense. These pseudorotaxane-based molecular devices exploit the so-called Texas-sized molecular box (cyclo[2]-(2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene); 14+, studied as its tetrakis-PF6− salt) as the wheel component. Anions of azobenzene-4,4′-dicarboxylic acid (2H+•2) or 4,4′-stilbenedicarboxylic acid (2H+•3) serve as the threading rod elements. The various forms of 2 and 3 (neutral, monoprotonated, and diprotonated) interact differently with 14+, as do the photoinduced cis or trans forms of these classic photoactive guests. The net result is a multimodal molecular switch that can be regulated in synergistic fashion through protonation/deprotonation and photoirradiation. The degree of guest protonation is the dominating control factor, with light acting as a secondary regulatory stimulus. The present dual input strategy provides a complement to more traditional orthogonal stimulus-based approaches to molecular switching and allows for the creation of nonbinary stimulus-responsive functional materials.

Chiral control of spin-crossover dynamics in Fe(II) complexes

Iron-based spin-crossover (SCO) complexes hold tremendous promise as multifunctional switches in molecular devices. However, real-world technological applications require the excited high-spin (HS) state to be kinetically stable – a feature that has only been achieved at cryogenic temperatures in the light-induced excited spin-state trapping effect. Here we demonstrate HS state trapping by controlling the chiral configuration of FeII(4,4’-dimethyl-2,2’-bipyridine)3 in solution, associated for stereocontrol with enantiopure ∆- or Λ-TRISPHAT anions. We characterize the HS state relaxation using a newly developed ultrafast circular dichroism technique in combination with transient absorption and anisotropy measurements. We find that the decay of the HS state is accompanied by ultrafast changes of its optical activity, reflecting the coupling to a symmetry-breaking torsional twisting mode, contrary to the commonly assumed picture. Furthermore, we show that the diastereoselective ion-pairing with the enantiopure anions suppresses the vibrational population of the identified twisting mode, thereby achieving a four-fold extension of the HS lifetime. Transferred to the solid state, this novel strategy may thus significantly improve the kinetic stability of iron(II)-based magnetic switches at room temperature.

Doubly linked chiral phenanthrene oligomers for homogeneously π-extended helicenes with large effective conjugation length

Helically twisted conductive nanocarbon materials are applicable to optoelectronic and electromagnetic molecular devices working on the nanometer scale. Herein, we report the synthesis of per-peri-perbenzo[5]- and [9]helicenes in addition to previously reported π-extended [7]helicene. The homogeneously π-extended helicenes can be regarded as helically fused oligo-phenanthrenes. The HOMO−LUMO gap decreased significantly from 2.14 to 1.15 eV with increasing helical length, suggesting the large effective conjugation length (ECL) of the π-extended helical framework. The large ECL of π-extended helicenes is attributed to the large orbital interactions between the phenanthrene subunits at the 9- and 10-positions, which form a polyene-like electronic structure. Based on the experimental results and DFT calculations, the ultrafast decay dynamics on the sub-picosecond timescale were attributed to the low-lying conical intersection.

Ultrahigh Spin Filter Efficiency, Giant Magnetoresistance and Large Spin Seebeck Coefficient in Monolayer and Bilayer Co-/Fe-/Cu-Phthalocyanine Molecular Devices

The spin related electrical and thermoelectric properties of monolayer and bilayer MPc (M = Co, Fe, Cu) molecular devices in a parallel spin configuration (PC) and an anti-parallel spin configuration (APC) between the V-shaped zigzag-edged graphene nanoribbon electrodes and the center bilayer MPc molecules are investigated by combining the density functional theory and non-equilibrium Green’s function approaches. The results show that there is an ultrahigh spin filter efficiency exceeding 99.99995% and an ultra-large total conductance of 0.49996G0 for FePc-CoPc molecular devices in PC and a nearly pure charge current at high temperature in an APC and a giant MR ratio exceeding 9.87 × 106% at a zero bias. In addition, there are pure spin currents for CuPc and FePc molecular devices in PC, and an almost pure spin current for FePc molecular devices in an APC at some temperature. Meanwhile, there is a high SFE of about 99.99585% in a PC and a reserved SFE of about −19.533% in an APC and a maximum MR ratio of about 3.69 × 108% for the FePc molecular device. Our results predict that the monolayer and bilayer MPc (M = Co, Fe, Cu) molecular devices possess large advantages in designing high-performance electrical and spintronic molecular devices.

Re-engineering Plant Phenylpropanoid Metabolism With the Aid of Synthetic Biosensors

Phenylpropanoids comprise a large class of specialized plant metabolites with many important applications, including pharmaceuticals, food nutrients, colorants, fragrances, and biofuels. Therefore, much effort has been devoted to manipulating their biosynthesis to produce high yields in a more controlled manner in microbial and plant systems. However, current strategies are prone to significant adverse effects due to pathway complexity, metabolic burden, and metabolite bioactivity, which still hinder the development of tailor-made phenylpropanoid biofactories. This gap could be addressed by the use of biosensors, which are molecular devices capable of sensing specific metabolites and triggering a desired response, as a way to sense the pathway’s metabolic status and dynamically regulate its flux based on specific signals. Here, we provide a brief overview of current research on synthetic biology and metabolic engineering approaches to control phenylpropanoid synthesis and phenylpropanoid-related biosensors, advocating for the use of biosensors and genetic circuits as a step forward in plant synthetic biology to develop autonomously-controlled phenylpropanoid-producing plant biofactories.