The Genesis of Molecular Electronics

Carroll, R. Lloyd; Gorman, Christopher B.

doi:10.1002/1521-3773(20021202)41:23<4378::aid-anie4378>3.0.co;2-a

Cited by 814 publications

(497 citation statements)

References 84 publications

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“…One particularly fascinating area is the application of switchable molecular building blocks in information storage. 88,89 In order to achieve this goal, however, a detailed understanding of the adsorption behaviour of large organic molecules on well-defined surfaces is essential, which has stimulated model investigations in an ultrahigh vacuum. A large number of studies have been performed using LT STM; this method not only allows for direct imaging of the adsorbed species in real space, but also opens up the possibility to manipulate the molecular objects.…”

Section: Conformational Switching Of Porphyrin Moleculesmentioning

confidence: 99%

Studying the dynamic behaviour of porphyrins as prototype functional molecules by scanning tunnelling microscopy close to room temperature

Marbach

Steinrück

2014

Chem. Commun.

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Scanning tunnelling microscopy (STM) enables us to directly observe the dynamic behaviour of organic molecules on surfaces. While imaging atoms and molecules using STM is certainly fascinating by itself, corresponding temperature-dependent measurements allow for the quantitative determination of the energetics and kinetics of the underlying molecular surface processes. Herein, we review recent advances in the STM investigation of the dynamic behaviour of adsorbed porphyrins at and close to room temperature.Three different case studies are discussed, providing insight into the dynamics of diffusion, rotation, reaction, and molecular switching at surfaces, based on isothermal STM measurements. The reviewed examples demonstrate that variable temperature STM can be a suitable tool to directly monitor the dynamic behaviour of individual adsorbed molecules, at and close to room temperature. Free base porphyrins on Cu(111) proved to be particularly suitable for these studies due to the strong bonding interaction between the iminic nitrogen atoms in the porphyrin macrocycle and the Cu substrate atoms. As a consequence, the corresponding activation energies for surface diffusion, self-metalation reaction and conformational switching are of a magnitude that allows for monitoring the processes at and around room temperature, in contrast to most previous studies, which were performed at cryogenic temperatures. The kinetic analysis of the surface diffusion and self-metalation was performed using an Arrhenius approach, yielding the corresponding activation energies and preexponential factors. In contrast, the conformational switching process was analysed in the framework of transition state theory, based on the Eyring equation. This approach provides a more detailed insight into interpretable thermodynamic potentials, i.e., the enthalpic and entropic contributions to the activation barrier. The analysis shows that at room temperature the adsorption and switching behaviour of the investigated free base porphyrin on Cu(111) is dominated by entropic effects. Since the entropic energy contribution vanishes at low temperatures, the importance of experiments conducted at temperatures close to room temperature is emphasized.

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Section: Conformational Switching Of Porphyrin Moleculesmentioning

confidence: 99%

Studying the dynamic behaviour of porphyrins as prototype functional molecules by scanning tunnelling microscopy close to room temperature

Marbach

Steinrück

2014

Chem. Commun.

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“…[154][156] [179] The concept of molecules as tailor made functional building blocks with atomic precision for electronic applications ranging from single molecules, [153] [253] through molecular devices, [254]- [258] to bulk materials leads to new challenges in organic chemistry. Of particular interest are conjugated systems as their delocalized electrons are expected to considerably favor electronic transport through their planer structures.…”

Section: Switchable Conducting Azo Biphenylsmentioning

confidence: 99%

Shape‐Switchable Azo‐Macrocycles

et al. 2009

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The synthesis of four shape‐switchable macrocycles comprising different peripheral substituents is described. The macrocycles 1–4 consist of m‐terphenyl semicircles interlinked by two azo joints. These macrocycles were assembled from nitro‐functionalized m‐terphenyl moieties through reductive dimerization. The semicircles were assembled through Suzuki cross‐coupling reactions. The molecular weights of the macrocycles were determined by vapour pressure osmometry, because mass spectrometry failed in the cases of 2 and 3. The E → Z photoisomerization reactions were analysed by UV/Vis spectroscopy complemented by 1H NMR studies. A very slow thermal back‐reaction indicated considerable stabilization of the Z isomer. The reduced efficiency of the thermal back‐reaction probably arises from the reduced degree of freedom due to the mechanical interlinking of the two azo groups. The photostationary state consisted of all‐Z (85 %) and all‐E isomers (15 %). The E → Z transformation induced by irradiation displayed simple exponential kinetics, which indicates pairwise switching of the two azo groups in a macrocycle, at least on the timescale under investigation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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“…2,3,7 Supramolecular arrays are of interest with respect to the study of energy transfer and photosynthetic mechanisms 7,8 while two-dimensional porphyrin assemblies have attracted attention for possible application as chemical sensors, in molecular electronics, or as chemically switchable 2D rotors. 3,9,10 Related to this, we recently showed that a porphyrin-functionalized silver surface exhibits ligand binding and unbinding reactions characteristic of the free metalloporphyrin 11 and showed that a well-chosen ligand can strongly alter the dynamics of adsorbed porphyrins. 10 Porphyrins have been attached to oxide surfaces for use as sensors by means of organophosphonate linkers.…”

Section: Introductionmentioning

confidence: 99%

Deprotection, Tethering, and Activation of a One-Legged Metalloporphyrin on a Chemically Active Metal Surface: NEXAFS, Synchrotron XPS, and STM Study of [SAc]P−Mn(III)Cl on Ag(100)

et al. 2009

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The structural and reactive properties of the acetyl-protected "one-legged" manganese porphyrin[SAc]P-Mn(III)Cl on Ag(100) have been studied by NEXAFS, synchrotron XPS and STM.Spontaneous surface-mediated de-protection occurs at 300 K accompanied by spreading of the resulting thio-tethered porphyrin across the metal surface. Loss of the axial chlorine ligand occurs at 498 K, without any de-metallation of the macrocycle, leaving the Mn center in a low co-ordination state. At low coverages the macrocycle is markedly tilted towards the silver surface, as is the phenyl group that forms part of the tethering "leg". In the monolayer region a striking transition occurs whereby the molecule rolls over, preserving the tilt angle of the phenyl group, strongly increasing that of the 2 macrocycle, decreasing the apparent height of the molecule and decreasing its footprint, thus enabling closer packing. These findings are in marked contrast with those previously reported for the corresponding more rigidly bound four-legged porphyrin [JACS 2009[JACS , 126, 1910 suggesting that the physico-chemical properties and potential applications of these versatile systems should be strongly dependent on the mode of tethering to the surface.

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The Genesis of Molecular Electronics

Cited by 814 publications

References 84 publications

Studying the dynamic behaviour of porphyrins as prototype functional molecules by scanning tunnelling microscopy close to room temperature

Studying the dynamic behaviour of porphyrins as prototype functional molecules by scanning tunnelling microscopy close to room temperature

Shape‐Switchable Azo‐Macrocycles

Deprotection, Tethering, and Activation of a One-Legged Metalloporphyrin on a Chemically Active Metal Surface: NEXAFS, Synchrotron XPS, and STM Study of [SAc]P−Mn(III)Cl on Ag(100)

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