Nonuniform STM Contrast of Self-Assembled Tri- n -octyl-triazatriangulenium Tetrafluoroborate on HOPG

International audienceWe have assembled 4,8,12-tri-n-octyl-4,8,12-triazatrianguleniumtetrafluoroborate (TATA-BF4) on highly oriented pyrolytic graphite (HOPG) and have studied the structure and tunneling properties of this self-assembled monolayer (SAM) using scanning tunneling microscopy (STM) under ambient conditions. We show that the triazatriangulenium cations TATA(+) form hexagonally packed structures driven by the interaction between the aromatic core and the HOPG lattice, as evidenced by density functional theory (DFT) modeling. According to the DFT results, the three alkyl chains of the platform tend to follow the main crystallographic directions of HOPG, leading to a different STM appearance. The STM contrast of the SAM shows that the monolayer is formed by two types of species, namely, TATA(+) with BF4- counterions on top and without them. The cationic TATA(+) platform gives rise to a seemingly higher appearance than neutral TATA-BF4, in contrast to observations made on metallic substrates. The variation of the STM tunneling parameters does not change the relative difference of contrast, revealing the stability of both species on HOPG. DFT calculations show that TATA-BF4 on HOPG has sufficient binding energy to resist dissociation into TATA(+) and BF4-, which might occur under the action of the electric field in the tunneling gap during STM scanning

Kinked row-induced chirality driven by molecule-substrate interactions

International audienceCombining STM measurements on three different substrates (HOPG, MoS2, and Au[111]), DFT calculations, and using a previously developed phenomenological model, we analyze the origin of the self-assembly of 4-Cyano-4′-n-decylbiphenyl (10CB), into kinked row structures. This molecule has an alkyl chain with 10 carbons and a cyanobiphenyl group of particularly large dipole moment. 10CB represents a toy model that we use here to unravel the relationship between the induced kinked structure, in particular, the corresponding chirality expression, and the balanced intermolecular/molecule-substrate interaction. We show that the local ordered structure is driven by the typical alkyl chain/substrate interaction for HOPG and Au[111] and the cyanobiphenyl group/substrate interaction for MoS2. The strongest molecule/substrate interactions are observed for MoS2 and Au[111]. These strong interactions should have led to non-kinked, commensurate adsorbed structures. However, this latter appears impossible due to steric interactions between the neighboring cyanobiphenyl groups that lead to a fan-shape structure of the cyanobiphenyl packing on the three substrates. As a result, the kink-induced chirality is particularly large on MoS2 and Au[111]. A further breaking of symmetry is observed on Au[111] due to an asymmetry of the facing molecules in the rows induced by similar interactions with the substrate of both the alkyl chain and the cyanobiphenyl group. We calculate that the overall 10CB/Au[111] interaction is of the order of 2 eV per molecule. The close 10CB/MoS2 interaction, in contrast, is dominated by the cyanobiphenyl group, being particularly large due to dipole-dipole interaction between the cyanobiphenyl groups and the MoS2 substrate

Optical properties of gold nanoparticles decorated with furan-based diarylethene photochromic molecules

The optical properties of the photochromic 1,2-bis(2-methyl-5-((4-mercaptophenyl)ethynyl)-furan-3-yl)perfluorocyclopentene (YnPhT) covalently attached to gold nanoparticles (AuNP) (d = 17 ± 1 nm) were studied in air at ambient conditions. The reversible ring-opening/closing photochromic reactions of molecules attached on AuNP surface can occur under similar light irradiation conditions as observed for free molecules in ethanolic solution. An unexpected blue shift of the local surface plasmon resonance band (LSPR) of AuNP covered by photochromic molecules was observed after UV light irradiation. A reverse red shift of LSPR was observed when the AuNP are illuminated by visible light. Moreover, increased amplitude of the LSPR was observed for AuNP covered with molecules in the closed-ring state. These observations are discussed in view of molecule – AuNP interactions. These interactions decelerate the kinetics of the ring-closing reaction of YnPhT on AuNP surfaces under UV light irradiation.publishe

Switching at the Nanoscale: Light- and STM-Tip-Induced Switch of a Thiolated Diarylethene Self-Assembly on Au(111)

International audienceThe light-induced and STM-tip-induced switching of photochromic thiol functionalized terphenylthiazole-based diarylethene self-assembly on Au(111) has been investigated in ambient conditions. For such a purpose, we took advantage of the formation of highly ordered domains of opened-ring (1o) or closed-ring (1c) diarylethene isomers. We evidenced a STM-tip-induced switching for the 1o isomer characterized by a tip bias threshold of 1000 mV above which switching of all molecules of the ordered 1o domains occurs into the 1c isomer. In contrast, switching from 1c form into 1o form is not observed at the same tunnelling conditions within a domain formed by ordered 1c molecules. We compared tip-induced switching of ordered 1o domains and switching of single 1o isomers embedded in 1c domains. This led to the demonstration that the process of switching of the 1o isomer is determined by geometry of the molecules but also that the stability of the switched 1c isomer depends on the nature of the surrounding isomers. We also compare tip-induced switching and switching under the action of external UV light irradiation of ordered 1o domains. In contrast with STM tip-induced switching, the UV light induces switching of 1o domains into their stable 1c form, in agreement with a collective switching under irradiation, which cannot occur under the action of STM tip

Ultrafast ring-closing reaction dynamics of a photochromic furan-based difurylethene

The ultrafast photoinduced ring-closing dynamics of a furan-based difurylethene (YnPhT) has been investigated by femtosecond transient absorption spectroscopy. We performed time-dependent density functional theory (TD-DFT) calculations to explain the experimental results in detail. The sub-picosecond time scale of the ring-closing reaction is comparable with thiophene-based analogues, but oxygen atoms at the photochromic core can avoid adverse interaction between switches and metal contacts in further applications. This observation proves that furan-based diarylethenes are potential optoelectronic elements with an ultrafast optical response.publishe

Picosecond cyclization reaction dynamics of furan-based diarylethene with thiosemicarbazone side-chain groups

Picosecond cyclization reaction dynamics of furan-based photochromic diarylethenes with thiosemicarbazone side-chains were studied by femtosecond transient absorption spectroscopy. The monitored ring-closing reaction in the time range of 0÷1100 ps is characterized by two main stages. First stage proceeds during the first 1.1 ps and is associated mainly with redistribution of π-π molecular orbitals of excited open-ring molecules which consequently leads to the formation of excited closed-ring molecules. During the next 300 ps, a long-term relaxation via vibrational cooling of closed-ring form occurs. The obtained relaxation dynamics curve was fitted by an exponential decay function with 68 ps time constant.publishe

STM Observation of Open- and Closed-Ring Forms of Functionalized Diarylethene Molecules Self-Assembled on a Au(111) Surface

International audienceSTM Observation of Open- and Closed-Ring Forms of Functionalized Diarylethene Molecules Self-Assembled on a Au(111) Surface Abstract HTMLFull Text HTML PDFHi-Res PDF[3988 KB] PDFPDF w/ Links[782 KB] Supporting Info Figures Your current credentials do not allow retrieval of the full text. Purchase the full-text Cart PDF/HTML, figures/images, references and tables, (where available) PDF Sergii V. Snegir†‡||, Alexandr A. Marchenko§, Pei Yu, Francois Maurel#, Oleksiy L. Kapitanchuk, Sandra Mazerat, Marc Lepeltier, Anne Léaustic, and Emmanuelle Lacaze*†|| Institut des NanoSciences de Paris (INSP), CNRS, 4 place Jussieu, 75251 Paris, France Institut des NanoSciences de Paris (INSP), UPMC Université Paris 6, 4 place Jussieu, 75251 Paris, France ‡Chuiko Institute of Surface Chemistry, §Institute of Physics, and Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, Kyiv, Ukraine Institut de Chimie Moléculaire et des Matériaux d'Orsay, UMR 8182, Université Paris Sud 11, 91405 Orsay, France Univ Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR CNRS 7086, 15 rue J-A de Baïf, 75205 Paris Cedex 13, France J. Phys. Chem. Lett., 2011, 2 (19), pp 2433-2436 DOI: 10.1021/jz200875c Publication Date (Web): August 24, 2011 Copyright © 2011 American Chemical Society E-mail: [email protected]. CASSection: Surface Chemistry and Colloids Abstract Abstract Image Ordered self-assembled monolayers (SAMs) of thiolated diarylethene photochromic molecules have been built on a Au(111) surface and characterized by mean of scanning tunneling microscopy (STM) for the first time. It has been revealed that molecules deposited from UV-illuminated (closed-ring isomer) and initial solutions (open-ring isomer) both occupy 4 × 2√3 adsorption sites on Au(111) and present a conformation where conjugated parts are parallel to the surface, forming "umbrella-like" structure. On the basis of the distances measured from STM images with intramolecular resolution and on quantum chemical DFT calculations of electronic structure for single molecules, an identical model of molecular packing with a 4 × 4√3 unit cell is proposed for both isomers. The variation of internal orbitals between open- and closed-ring isomers leads to significant change of STM contrast, allowing direct identification of each diarylethene isomer using STM images

Gold Nanoparticle Self-Aggregation on Surface with 1,6-Hexanedithiol Functionalization

Here we study the morphology and the optical properties of assemblies made of small (17 nm) gold nanoparticles (AuNPs) directly on silicon wafers coated with (3-aminopropyl)trimethoxysilane (APTES). We employed aliphatic 1,6-hexanedithiol (HDT) molecules to cross-link AuNPs during a two-stage precipitation procedure. The first immersion of the wafer in AuNP colloidal solution led mainly to the attachment of single particles with few inclusions of dimers and small aggregates. After the functionalization of precipitated NPs with HDT and after the second immersion in the colloidal solution of AuNP, we detected a sharp rise in the number of aggregates compared to single AuNPs and their dimers. The lateral size of the aggregates was about 100 nm, while some of them were larger than 1μm. We propose that the uncompensated dipole moment of the small aggregates appeared after the first precipitation and acts further as the driving force accelerating their further growth on the surface during the second precipitation. By having such inhomogeneous surface coating, the X-ray reciprocal space maps and modulation polarimetry showed well-distinguished signals from the single AuNPs and their dimers. From these observations, we concluded that the contribution from aggregated AuNPs does not hamper the detection and investigation of plasmonic effects for AuNP dimers. Meantime, using unpolarized and polarized light spectroscopy, the difference in the optical signals between the dimers, being formed because of self-aggregation and the one being cross-linked by means of HDT, was not detected.publishe

On a specific state of C60_{60} fullerene in N-methyl-2-pyrrolidone solution: Mass spectrometric study

A solution of fullerene C$_{60}$ in N-methylpyrrolidone (NMP) presents a suitable system for obtaining fullerene's clusters with the tunable size. However, the mechanism of fullerenes interaction with polar NMP molecules is still elusive. Herein, we present the measured laser desorption/ionization mass spectra (LDI MS) of the precipitates produced from C$_{60}$/NMP solutions of different age in comparison with the typical spectra of C$_{60}$ crystallized from toluene and benzene. The distinctive characteristics of the C$_{60}$/NMP mass spectra were identified and carefully examined. The number of characteristic peaks and their relative intensities in the spectra strongly depend on the age of initial C$_{60}$/NMP solutions. This effect was attributed to the specific C$_{60}$-NMP interactions in the solution, namely to the formation of charge-transfer complexes of C$_{60}$ with NMP molecules followed by fullerene cluster formation. The results of additional measurements carried out by means of small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR), UV–Vis absorption spectroscopy together with the density functional theory (DFT) calculations are in accord with the proposed hypothesis

STM Observation of Open- and Closed-Ring Forms of Functionalized Diarylethene Molecules Self-Assembled on a Au(111) Surface

Ordered self-assembled monolayers (SAMs) of thiolated diarylethene photochromic molecules have been built on a Au(111) surface and characterized by mean of scanning tunneling microscopy (STM) for the first time. It has been revealed that molecules deposited from UV-illuminated (closed-ring isomer) and initial solutions (open-ring isomer) both occupy 4 × 2√3 adsorption sites on Au(111) and present a conformation where conjugated parts are parallel to the surface, forming “umbrella-like” structure. On the basis of the distances measured from STM images with intramolecular resolution and on quantum chemical DFT calculations of electronic structure for single molecules, an identical model of molecular packing with a 4 × 4√3 unit cell is proposed for both isomers. The variation of internal orbitals between open- and closed-ring isomers leads to significant change of STM contrast, allowing direct identification of each diarylethene isomer using STM images