Covalent Self-assembly Research Articles

Tris(thioacetals) from benzene hexathiol: towards covalent self-assembly.

Mixtures of isomers are available from the reaction of benzene hexathiol with three equivalents of p-tolualdehyde and kinetic traps avoided under the reported catalytic conditions, establishing tris(thioacetals) as potential building blocks for covalently self-assembled complex structures.

Nanoscale Consecutive Self-Assembly of Thin-Film Molecular Materials for Electrooptic Switching. Chemical Streamlining and Ultrahigh Response Chromophores

A broadly applicable approach to formation of self-assembled organic electrooptic superlattices for high-speed switching is reported. This two-step “one-pot” method involves (i) layer-by-layer covalent self-assembly of intrinsically acentric monolayers of a new high-hyperpolarizability donor−acceptor aminophenylbenzothiazolpyridinium chromophore (β(0.65 eV)calcd = 1620 × 10-30 cm5 esu-1) on hydrophilic substrates and (ii) in-situ chromophore deprotection concurrent with self-limiting “capping”/planarization of each chromophore layer with octachlorotrisiloxane. The resulting organic films are characterized using a combination of physicochemical methodolgies including synchrotron X-ray specular reflectivity, angle-dependent polarized second harmonic generation spectroscopy, optical spectrometry, X-ray photoelectron spectroscopy, and advancing contact angle measurements. The superlattices exhibit very large second-order responses, χ(2) ≈ 370 pm/V, and a large macroscopic electrooptic coefficient, r33 ≈ 120 pm/V, is estimated at λ0 = 1064 nm.

Nanoscale Refractive Index Tuning of Siloxane-Based Self-Assembled Electro-Optic Superlattices

The refractive indices of self-assembled organic electro-optic superlattices can be tuned by intercalating high-Z optically transparent group 13 metal oxide sheets into the structures during the self-assembly process. Microstructurally regular acentricity and sizable electro-optic responses are retained in this straightforward synthetic procedure. This “one-pot” all wet-chemistry approach involves: i) layer-by-layer covalent self-assembly of intrinsically acentric multilayers of high-hyperpolarizability chromophores on inorganic oxide substrates, ii) protecting group cleavage to generate a large density of reactive surface hydroxyl sites, iii) self-limiting capping of each chromophore layer with octachlorotrisiloxane, iv) deposition of metal oxide sheets derived from THF solutions of Ga(OiC3H7)3 or In(OiC3H7)3, and v) covalent capping of the resulting superlattices.

Nanoscale Covalent Self-Assembly Approach to Enhancing Anode/Hole-Transport Layer Interfacial Stability and Charge Injection Efficiency in Organic Light-Emitting Diodes

The integrity of electrode/organic interfacial contact is shown to be crucial to the performance and stability of organic light-emitting diodes (OLEDs). In this contribution, vapor-deposited lipophilic, hole-transporting N,N‘-diphenyl-N,N‘-bis(3-methylphenyl)[1,1‘-biphenyl]-4,4‘-diamine (TPD) films are shown to undergo dewetting on indium tin oxide (ITO) anode surfaces under mild heating. An effective approach to minimize this interfacial decohesion effect is by small hole transport molecule self-assembly on the anode surface. Thus, conformal N(p-C6H4CH2CH2CH2SiCl3)3 (TAA)-based monolayers can be covalently self-assembled from solution onto hydroxylated ITO surfaces. The resulting nanometer-scale-thick TAA layers (∼11 A/layer) prevent dewetting of the vapor-deposited TPD hole transport layers. Furthermore, ITO/(TAA)n/TPD/Alq/Al structured OLED devices fabricated with these modified ITO−TPD interfaces exhibit, as a function of n, reduced turn-on voltages as well as considerably higher luminous intensities ...

Covalent self-assembly of a dimeric borazaaromatic macrocycle†

Bis(10-hydroxy-10,9-boraza-2-phenanthryl) ether is capable of covalent self-assembly upon dehydration in solution to form the corresponding cyclic dimer.

Luminescent transition-metal-containing cyclophanes (“molecular squares”): covalent self-assembly, host-guest studies and preliminary nanoporous materials applications

An overview is given of the synthesis and characterization of a family of transition-metal cyclophanes containing rhenium tricarbonyl chloro corners and bridging diimine edges. The synthesis of both heterometallic (Re2M2,M = Pd,Pt) and homometallic (Re4) cyclophanes is described. Also briefly described are studies aimed at shedding light on the probable mechanism of high-yield assembly of homometallic molecular squares. The use of these cavity-containing assemblies as hosts in the condensed-phase binding of selected molecular guests is discussed. Also described are preliminary applications of the compounds as thin film nanoporous sensing elements. These studies suggest that the compounds may prove useful in mass-responsive or light-responsive volatile organic chemical sensing devices.

Automated Recognition, Sorting, and Covalent Self-Assembly by Predisposed Building Blocks in a Mixture

Automated Recognition, Sorting, and Covalent Self-Assembly by Predisposed Building Blocks in a Mixture

Kinetic Control of Interparticle Spacing in Au Colloid-Based Surfaces: Rational Nanometer-Scale Architecture

This paper details the kinetic aspects of covalent self-assembly of colloidal Au particles from solution onto immobilized organosilane polymers. On glass substrates, surface formation can be monitored using UV−vis spectroscopy and field emission scanning electron microscopy (FE-SEM). Correlation of these data allows the effect of nanostructure on bulk optical properties to be evaluated. At short derivatization times, particle coverage is proportional to (time)1/2. The particle sticking probability p, defined as the ratio of bound particles to the number of particles reaching the surface in a given time period, can be determined from a knowledge of the particle radius, solution concentration, temperature, and solution viscosity; for surfaces derivatized with (3-mercaptopropyl)trimethoxysilane (MPTMS), p ≈ 1. At longer derivatization times, interparticle repulsions result in a “saturation” coverage at ≈30% of a close-packed monolayer. Two approaches for modulating the rate of surface formation are described: electrochemical potential control on organosilane-modified SnO2 electrodes and charge screening by organic adsorbates. Self-assembly of colloidal Au particles onto functionalized substrate surfaces is a reproducible phenomenon, as evidenced by UV−vis and surface enhanced Raman scattering (SERS) measurements on identically prepared substrates.

Frequency-Dependent Second Harmonic Generation in Acentric Chromophoric Self-Assembled NLO Materials

ABSTRACTAn attractive and challenging approach to the construction of robust, thin film materials with large second-order optical nonlinearities is the covalent self-assembly of aligned arrays of high-β molecular chromophores into multilayer superlattices. In this paper, we describe the dispersion of second harmonic generation (SHG) in a self-assembled (SA) monolayer containing a stilbazolium chromophore. The frequency-dependent measurements were performed on 25 Å thick monolayers on glass using a tunable (0.4–2 μm) light source based on optical parametric amplification (OPA). The SHG spectrum contains a clear two-photon resonance at hω = 1.3eV. The maximum in the second-order susceptibility coincides with a low energy chromophore-centered charge-transfer excitation at 480 nm. The experimental SHG dispersion values compare favorably with theoretical results computed using a sum-over-states (SOS) formalism. However, the measured values exhibit a somewhat broader band response than the theoretical curve, and the origin of this behavior is discussed.