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1.
J Chem Inf Model ; 60(4): 2155-2168, 2020 04 27.
Artigo em Inglês | MEDLINE | ID: mdl-32155335

RESUMO

Due to their unique geometry complex, self-assembled nanoporous 2D molecular crystals offer a broad landscape of potential applications, ranging from adsorption and catalysis to optoelectronics, substrate processes, and future nanomachine applications. Here we report and discuss the results of extensive all-atom Molecular Dynamics (MD) investigations of self-assembled organic monolayers (SAOM) of interdigitated 1,3,5-tristyrilbenzene (TSB) molecules terminated by alkoxy peripheral chains Cn containing n carbon atoms (TSB3,5-Cn) deposited onto highly ordered pyrolytic graphite (HOPG). In vacuo structural and electronic properties of the TSB3,5-Cn molecules were initially determined using ab initio second order Møller-Plesset (MP2) calculations. The MD simulations were then used to analyze the behavior of the self-assembled superlattices, including relaxed lattice geometry (in good agreement with experimental results) and stability at ambient temperatures. We show that the intermolecular disordering of the TSB3,5-Cn monolayers arises from competition between decreased rigidity of the alkoxy chains (loss of intramolecular order) and increased stabilization with increasing chain length (afforded by interdigitation). We show that the inclusion of guest organic molecules (e.g., benzene, pyrene, coronene, hexabenzocoronene) into the nanopores (voids formed by interdigitated alkoxy chains) of the TSB3,5-Cn superlattices stabilizes the superstructure, and we highlight the importance of alkoxy chain mobility and available pore space in the dynamics of the systems and their potential application in selective adsorption.


Assuntos
Grafite , Simulação de Dinâmica Molecular , Nanoporos , Adsorção , Derivados de Benzeno , Conformação Molecular
2.
Nanoscale ; 11(44): 21284-21290, 2019 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-31667485

RESUMO

Nano-porous two-dimensional molecular crystals, self-assembled on atomically flat host surfaces offer a broad range of possible applications, from molecular electronics to future nano-machines. Computer-assisted designing of such complex structures requires numerically intensive modeling methods. Here we present the results of extensive, fully atomistic simulations of self-assembled monolayers of interdigitated molecules of 1,3,5-tristyrilbenzene substituted by C6 alkoxy peripheral chains (TSB3,5-C6), deposited onto highly-ordered pyrolytic graphite. Structural and electronic properties of the TSB3,5-C6 molecules were determined from ab initio calculations, then used in Molecular Dynamics simulations to analyze the mechanism of formation, epitaxy, and stability of the TSB3,5-C6 nanoporous superlattice. We show that the monolayer disordering results from the competition between flexibility of the C6 chains and their stabilization by interdigitation. The inclusion of guest molecules (benzene and pyrene) into superlattice nanopores stabilizes the monolayer. The alkoxy chain mobility and available pore space defines the systems dynamics, essential for potential application.

3.
Chem Commun (Camb) ; 54(69): 9607-9610, 2018 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-30094435

RESUMO

We compare by Scanning Tunneling Microscopy (STM) self-organized honeycomb monolayers of aromatic molecules formed either on graphite or on graphene. A differential contrast between the adsorption sites observed exclusively on graphite evidences the electronic effects of the symmetry breaking by the staggered atomic layers forming this substrate.

4.
Phys Chem Chem Phys ; 20(17): 12295-12302, 2018 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-29687806

RESUMO

Two-photon luminescence (TPL) turn-off in small single gold nanorods (GNRs) exposed to increased resonant femtosecond laser excitation (800 nm wavelength, pulse energy density varying from 125 µJ cm-2 to 2.5 mJ cm-2) is investigated. The origin is shown to be a photo-induced decrease of the rod aspect ratio. This aspect ratio reduction could reasonably be assigned to gold atom diffusion away from the rod tips, where hot spots are localized. The two-photon luminescence signal can be recovered after a blue-shift of the incident excitation wavelength. No change in the excitation wavelength results in an out of resonance excitation of the rods and thus a reduced absorption, acting as feedback to stabilize the GNR shape and size. A theoretical analysis is presented evidencing limited thermal effects in the femtosecond regime for small nanoparticles, in good agreement with complementary topographic characterizations using scanning electron microscopy (SEM) and atomic force microscopy (AFM). We show finally that TPL reveals itself as a highly sensitive tool to follow tiny changes resulting from the photo-induced reshaping of GNRs.

5.
Langmuir ; 33(44): 12759-12765, 2017 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-29028348

RESUMO

We propose a novel approach to trap 2 nm Pt nanocrystals using nanoporous two-dimensional supramolecular networks for cavity-confined host-guest recognition process. This will be achieved by taking advantage of two features of supramolecular self-assembly at surfaces: First, its capability to allow the formation of complex 2D architectures, more particularly, nanoporous networks, through noncovalent interactions between organic molecular building-blocks; second, the ability of the nanopores to selectively host and immobilize a large variety of guest species. In this paper, for the first time, we will use isotropic honeycomb networks and anisotropic linear porous supramolecular networks to host 2 nm Pt nanocrystals.

6.
ACS Nano ; 11(7): 6728-6738, 2017 07 25.
Artigo em Inglês | MEDLINE | ID: mdl-28640628

RESUMO

We show that the use of oriented linear arrays of smectic A defects, the so-called smectic oily streaks, enables the orientation of gold nanorods (GNRs) for a large range of GNR diameters, ranging from 7 to 48 nm, and for various ligands. For the small GNRs it enables oriented end-to-end small chains of GNRs when the density is increased from around 2 GNRs/µm2 to around 6 GNRs/µm2. We have characterized the orientation of single GNRs by spectrophotometry and two-photon luminescence (TPL). A strongly anisotropic absorption of the composites and an on-off switching of GNR luminescence, both controlled by incident light polarization, are observed, revealing an orientation of the GNRs mostly parallel to the oily streaks. A more favorable trapping of GNRs by smectic dislocations with respect to ribbon-like defects is thus demonstrated. The dislocations appear to be localized at a specific localization, namely, the summit of rotating grain boundaries. Combining plasmonic absorption measurements, TPL measurements, and simulation of the plasmonic absorption, we show that the end-to-end GNR chains are both dimers and trimers, all parallel to each other, with a small gap between the coupled GNRs, on the order of 1.5 nm, thus associated with a large red-shift of 110 nm of the longitudinal plasmonic mode. A motion of the GNRs along the dislocations appears as a necessary ingredient for the formation of end-to-end GNR chains, the gap value being driven by the balance between the attracting van der Waals interactions and the steric repulsion between the GNRs and leading to interdigitation of the neighboring ligands. We thus obtain electromagnetic coupling of nanorods controlled by light polarization.

7.
Beilstein J Nanotechnol ; 7: 862-8, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27547603

RESUMO

A well-organized monolayer of alkylated perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) has been formed onto CVD graphene transferred on a transparent substrate. Its structure has been probed by scanning tunnelling microscopy and its optical properties by polarized transmission spectroscopy at varying incidence. The results show that the transition dipoles of adsorbed PTCDI are all oriented parallel to the substrate. The maximum absorption is consistent with the measured surface density of molecules and their absorption cross section. The spectrum presents mainly a large red-shift of the absorption line compared with the free molecules dispersed in solution, whereas the relative strengths of the vibronic structures are preserved. These changes are attributed to non-resonant interactions with the graphene layer and the neighbouring molecules.

8.
Org Biomol Chem ; 14(1): 358-70, 2016 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-26599863

RESUMO

On the basis of our previous work on DNA fluorophores derived from vinylpyridinium-triphenylamine, we explored the structure space around the electron-rich triphenylamine (TP) core by changing the vinyl bond to an oxazole ring. As 2,5-diaryloxazoles are known to be highly fluorescent and efficient two photon absorbers, we synthesized analogues with two different connections of the oxazole to the triphenylamine core: TP-Ox2Py and TP-Ox5Py sets. Since the benzimidazolium group was proven to be more effective in the TP series than the pyridinium, we also synthesized a TP-Ox5Bzim set. The TP-Ox5Py series retains the TP-Py properties: on/off behavior on DNA, good two-photon cross-section and bright staining of nuclear DNA by microscopy under both one or two-photon excitation. On the other hand, the TP-Ox2Py series does not display fluorescence upon binding to DNA. The TP-Ox5Bzim set is fluorescent even in the absence of DNA and displays lower affinity than the corresponding TP-Ox5Py. CD experiments and docking were performed to understand these different behaviors.


Assuntos
Compostos de Anilina/química , Sondas de DNA/química , DNA/química , Fluorescência , Oxazóis/química , Fótons , Corantes Fluorescentes/química , Estrutura Molecular
9.
Chemphyschem ; 16(18): 3774-8, 2015 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-26488211

RESUMO

2D supramolecular self-assembly is a good way to form well-defined nanostructures on various substrates. One of the current challenges is to extend this approach to 3D functional building blocks. Here, we address this issue by providing a strategy for the controlled lifting and positioning of functional units above a graphitic substrate. This is the first time that multistory cyclophane-based 3D tectons incorporating C60 units have been designed and synthesized. Molecular modelling provides a description of the 3D geometries and evidences the flexible character of the building blocks. Despite this later feature, the supramolecular self-assembly of Janus tectons on HOPG yields well-ordered adlayers incorporating C60 arrays at well-defined mean distances from the surface. As our approach is not limited to C60 , the results reported here open-up possibilities for applications where the topological and electronic interactions between the substrate and the functional unit are of prime importance.

10.
Beilstein J Nanotechnol ; 6: 632-9, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25821703

RESUMO

Two-dimensional (2D), supramolecular self-assembly at surfaces is now well-mastered with several existing examples. However, one remaining challenge to enable future applications in nanoscience is to provide potential functionalities to the physisorbed adlayer. This work reviews a recently developed strategy that addresses this key issue by taking advantage of a new concept, Janus tecton materials. This is a versatile, molecular platform based on the design of three-dimensional (3D) building blocks consisting of two faces linked by a cyclophane-type pillar. One face is designed to steer 2D self-assembly onto C(sp(2))-carbon-based flat surfaces, the other allowing for the desired functionality above the substrate with a well-controlled lateral order. In this way, it is possible to simultaneously obtain a regular, non-covalent paving as well as supramolecular functionalization of graphene, thus opening interesting perspectives for nanoscience applications.

11.
Nanotechnology ; 25(43): 435604, 2014 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-25297935

RESUMO

Specific molecular tectons can be designed to form molecular sieves through self-assembly at the solid-liquid interface. After demonstrating a model tecton bearing apolar alkyl chains, we then focus on a modified structure involving asymmetric functionalization of some alkyl chains with polar hydroxyl groups in order to get chemical selectivity in the sieving. As the formation of supramolecular self-assembled networks strongly depends on molecule-molecule, molecule-substrate and molecule-solvent interactions, we compared the tectons' self-assembly on graphite for two types of solvent. We demonstrate the possibility to create hydroxylated stilbenoid molecular sieves by using 1-decanol as a solvent. Interestingly, with this solvent, the porous network is developed on top of a 1-decanol monolayer.

12.
Angew Chem Int Ed Engl ; 53(38): 10060-6, 2014 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-25047257

RESUMO

A general strategy for simultaneously generating surface-based supramolecular architectures on flat sp(2) -hybridized carbon supports and independently exposing on demand off-plane functionality with controlled lateral order is highly desirable for the noncovalent functionalization of graphene. Here, we address this issue by providing a versatile molecular platform based on a library of new 3D Janus tectons that form surface-confined supramolecular adlayers in which it is possible to simultaneously steer the 2D self-assembly on flat C(sp(2))-based substrates and tailor the external interface above the substrate by exposure to a wide variety of small terminal chemical groups and functional moieties. This approach is validated throughout by scanning tunneling microscopy (STM) at the liquid-solid interface and molecular mechanics modeling studies. The successful self-assembly on graphene, together with the possibility to transfer the graphene monolayer onto various substrates, should considerably extend the application of our functionalization strategy.

13.
J Am Chem Soc ; 135(34): 12697-706, 2013 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-23914799

RESUMO

We report on the design and synthesis of two-photon fluorescent triphenylamines bearing two or three vinyl branches terminated by a N-methyl benzimidazolium moiety. The new compounds (TP-2Bzim, TP-3Bzim) are light-up fluorescent DNA probes with a long wavelength emission (>580 nm). Compared to their pyridinium models, the TP-Bzim dyes exhibit a remarkable improvement of both their DNA affinity and fluorescence quantum yield, especially for the two-branch derivative (TP-2Bzim: ΦF = 0.54, Ka = 10(7) M(-1)), resulting in a large fluorescence emission turn-on ratio of up to 140. Concomitantly, the two-photon absorption cross-section of TP-2Bzim is dramatically enhanced upon DNA binding (δ = 1080 vs 110 GM for the free form). This effect of the DNA matrix on the nonlinear absorption is uncovered for the first time. This is attributed to a tight fit of the molecule inside the minor groove of AT-rich DNA which induces geometrical rearrangements in the dye ground state as supported by circular dichroism and molecular modeling data. Consequently, TP-2bzim displays an exceptional two-photon molecular brightness (δ×ΦF = 583 GM), a value unrivalled for a small biofluorophore. These properties enable to image nuclear DNA in fixed cells at submicromolar concentration ([TP-2Bzim] = 100 nM) and to visualize ultrabright foci of centromeric AT-rich chromatin. Finally TP-2Bzim exhibits a high photostability, is live-cell permeant, and does not require RNase treatment. This outstanding combination of optical and biological properties makes TP-2Bzim a bioprobe surpassing the best DNA stainers and paves the way for studying further nonlinear optical processes in DNA.


Assuntos
Compostos de Anilina/química , Sondas de DNA/química , DNA/química , Corantes Fluorescentes/química , Fótons , Células 3T3 , Compostos de Anilina/síntese química , Animais , Células Cultivadas , Sondas de DNA/síntese química , Corantes Fluorescentes/síntese química , Células HT29 , Humanos , Camundongos , Modelos Moleculares
14.
Nanoscale ; 5(4): 1452-5, 2013 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-23306668

RESUMO

Taking into account substrate crystallographic constraints, an overarching molecular binding motif has been designed to allow transferable self-assembling patterns on different substrates. This optimized clip demonstrates robust and equivalent self-assembled architectures on both highly oriented pyrolitic graphite (HOPG) and reconstructed Au(111) surfaces.


Assuntos
Cristalização/métodos , Ouro/química , Grafite/química , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Sítios de Ligação , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
15.
Org Biomol Chem ; 10(30): 6054-61, 2012 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-22614341

RESUMO

On the basis of our previous work on vinyl-triphenylamine derived DNA fluorophores we explored the structure space around this core by coupling it to diverse cationic, anionic and zwitterionic groups in the aim of targeting different classes of biomolecules. In parallel core modifications were performed to optimize the photophysical properties (quantum yield, two-photon absorption). The resulting water soluble π-conjugated molecules are called TP dyes and display an exceptional combination of optical properties: high two-photon absorption cross-section, high photostability, no self-quenching, and switchable fluorescence emission when bound to a biopolymer matrix. The linear and nonlinear optical properties of the TP dyes were studied in vitro in presence of DNA and in presence of a model protein (human serum albumin) using complementary absorption and fluorescence spectroscopy characterization tools. Structure modifications enabled to switch from DNA probes (cationic TP-pyridinium series) to protein probes (anionic TP-rhodanine series) without affecting the optical properties. Finally most TP compounds appear cell-permeant and show an intracellular localization consistent with their in vitro target specificity.


Assuntos
Aminas/química , DNA/metabolismo , Imagem Molecular/métodos , Fótons , Albumina Sérica/metabolismo , Compostos de Vinila/química , Compostos de Vinila/metabolismo , Corantes Fluorescentes/síntese química , Corantes Fluorescentes/química , Corantes Fluorescentes/metabolismo , Células HT29 , Humanos , Fenômenos Ópticos , Coloração e Rotulagem , Compostos de Vinila/síntese química
16.
Opt Express ; 20(8): 8974-81, 2012 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-22513608

RESUMO

We study the propagation properties of surface plasmon polaritons on a Cu surface by means of photoemission electron microscopy. Use of a CMOS process to fabricate the Cu thin film is shown to enable very high propagation distances (up to 65 µm at 750 nm wavelength), provided that the copper native oxide is removed. A critical review of the optical loss mechanisms is undertaken and shed light on the effect of single grain boundaries in increasing the propagation losses of the plasmon. A microscopic interpretation is provided, relying on groove induced electromagnetic hot spots.

17.
Langmuir ; 27(16): 10251-5, 2011 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-21721572

RESUMO

Whereas molecular electronics needs well-controlled 3D geometries for decoupling or interconnecting individual molecules, conjugated polymers form disordered structures when deposited on a substrate. We show that this trend can be overcome in polythiophene derivatives designed so as to exploit weak sulfur-bromine interactions. A self-template effect follows, leading to staggered organizations of well-aligned electronically decoupled conjugated strands, as observed in situ by scanning tunneling microscopy and spectroscopy on graphite.

19.
J Chem Phys ; 134(12): 124702, 2011 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-21456690

RESUMO

The temperature and concentration dependences of the self-assembly onto graphite from solution of a series of molecular building blocks able to form nanoporous structures are analyzed experimentally by in situ scanning tunneling microscopy. It is shown that the commonly observed coexistence of dense and nanoporous domains results from kinetic blockades rather than a thermodynamic equilibrium. The ripening can be favored by high densities of domain boundaries, which can be obtained by cooling the substrate before the nucleation and growth. Then ripening at higher-temperature yields large defect-free domains of a single structure. This thermodynamically stable structure can be either the dense or the nanoporous one, depending on the tecton concentration in the supernatant solution. A sharp phase transition from dense to honeycomb structures is observed at a critical concentration. This collective phenomenon is explained by introducing interactions between adsorbed molecules in the thermodynamic description of the whole system.

20.
Nano Lett ; 11(2): 402-7, 2011 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-21244014

RESUMO

Plasmonic hotspots in single gold nanostars are located at the tips and can be excited selectively by laser light as evidenced by photoelectron emission microscopy. Selectivity is achieved through wavelength and polarization of the excitation light. Comparing photoelectron emission intensity and dark-field scattering spectra of the same individual nanostars reveals differences in terms of observable plasmon resonance wavelengths and field enhancements. Differences are explained with the underlying near- and far-field processes of the two techniques.


Assuntos
Ouro/química , Lasers , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Ressonância de Plasmônio de Superfície/métodos , Teste de Materiais , Tamanho da Partícula , Espalhamento de Radiação
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