Photocatalytic patterning of monolayers for the site-selective deposition of quantum dots onto TiO2 surfaces

A novel photochemical mechanism is reported for the site-selective deposition of quantum dots onto nanocrystalline TiO2 films. The patterning mechanism involves the combination of surfactant-mediated self-assembly and monolayer photolithography. In the self-assembly process, CdS and CdSe quantum dots were attached to TiO2 surfaces through bifunctional mercaptoalkanoic acid (MAA) linkers. MAAs were adsorbed to the TiO2 surface as the deprotonated carboxylates, primarily through monodentate coordination to Ti4+ sites. CdSe quantum dots were bound to the terminal thiol groups of surface-adsorbed MAAs, with a surface adduct formation constant, Kad, of (2.1 +/- 0.7) x 104 M-1. The color and optical density of the quantum dot-functionalized TiO2 films were tunable. Monolayer photopatterning involved the TiO2-catalyzed oxidative degradation of surface-adsorbed mercaptohexadecanoic acid (MHDA). A mechanism is proposed wherein MHDA degradation occurs through both oxidative decarboxylation and the formation of interchain disulfides. These MHDA photodegradation processes regulate the extent to which CdSe quantum dots adsorb onto the TiO2 surface. Illumination through a photomask yielded optically patterned, quantum dot-functionalized TiO2 films that were characterized by scanning electron microscopy and energy-dispersive X-ray analysis.     

Temporal evolution of the composition of mixed monolayers on TiO2 surfaces: evidence for a dimerization-induced chelate effect

Mixed monolayers of octanoic acid (OA) and 16-mercaptohexadecanoic acid (MHDA) were adsorbed to nanocrystalline TiO(2) films from mixed solutions in tetrahydrofuran. For a range of solution compositions, the mole fraction of MHDA within the mixed monolayers (chi (MHDA,surf)) exceeded that of the coadsorption solution. In addition, chi (MHDA,surf) increased with time, while the sum of the surface coverages of MHDA and OA remained constant. To account for these effects, we propose a mechanism involving disulfide formation between the terminal thiol groups of surface-adsorbed MHDA molecules. Disulfide formation leads to an increase in the surface adduct formation constant ( K(ad)) of dimeric MHDA, causing the gradual displacement of OA from the surface. The mechanism is supported by spectroscopic evidence and desorption kinetics. These are the first examples of mixed monolayers that undergo time-dependent compositional changes as a result of covalent bond formation between surfactants. Our findings illustrate that dimerization and other intermolecular interactions between surfactants may dramatically influence the composition and terminal functionalization of a wide range of mixed monolayer systems.     

Quantum dot solar cells. harvesting light energy with CdSe nanocrystals molecularly linked to mesoscopic TiO2 films

By using bifunctional surface modifiers (SH-R-COOH), CdSe quantum dots (QDs) have been assembled onto mesoscopic TiO(2) films. Upon visible light excitation, CdSe QDs inject electrons into TiO(2) nanocrystallites. Femtosecond transient absorption as well as emission quenching experiments confirm the injection from the excited state of CdSe QDs into TiO(2) nanoparticles. Electron transfer from the thermally relaxed s-state occurs over a wide range of rate constant values between 7.3 x 10(9) and 1.95 x 10(11) s(-1). The injected charge carriers in a CdSe-modified TiO(2) film can be collected at a conducting electrode to generate a photocurrent. The TiO(2)-CdSe composite, when employed as a photoanode in a photoelectrochemical cell, exhibits a photon-to-charge carrier generation efficiency of 12%. Significant loss of electrons occurs due to scattering as well as charge recombination at TiO(2)/CdSe interfaces and internal TiO(2) grain boundaries.     

The interaction between some diamines and CdSe quantum dots

The interaction of some diamines (ethylenediamine (EDA), 1,6-hexanediamine (HDA), o-phenylenediamine (OPD)) with CdSe quantum dots (QDs) is reported. With increasing concentration of EDA from 0 to 2.0 x 10(-6) mol l(-1), slight fluorescence enhancement is observed. However, the CdSe QDs fluorescence quenching is seen at relatively higher concentration of EDA. There is a red-shift of 0-7 nm in fluorescence emission spectra of CdSe QDs when the concentration of EDA is changed from 2.0 x 10(-6) to 8.0 x 10(-6) mol l(-1). The resonance light scattering (RLS) spectra of CdSe QDs have little change when the concentration of EDA is less than 5.0 x 10(-6) mol l(-1). It indicates there are little large particles formed in the solution. However, a significant increase of the RLS is observed in the 300-500 nm wavelength range after adding higher concentration than 5.0 x 10(-6) mol l(-1) EDA, which could be attributed to the large particles formed. The interaction between HDA and CdSe QDs is similar to that of EDA. However, with the OPD, it is found that the interaction is much different from those of EDA, HDA, and that the quenching, even at low concentration, is effective for CdSe QDs emission. The quenching phenomenon could be explained by a surface bound complexation equilibrium model.     

Preparation of colloidal CdSe and CdS/CdSe nanoparticles from sodium selenosulfate in aqueous polymers solutions

Cadmium selenide nanoparticles formation at the interaction between CdCl2 and Na2SeSO3 in aqueous solutions of sodium polyphosphate and gelatin has been studied. Structural and optical properties of CdSe nanoparticles have been characterized. It has been shown that the temperature and the ratio of reagents concentrations are the basic parameters, controlling the size of CdSe nanoparticles. Photocatalytic activity of CdS nanoparticles in Na2SeSO3 reduction has been found and investigated; structural and optical properties of binary CdS/CdSe nanoparticles have been characterized. This photoreaction, when carried out in the presence of CdCl2, results in the formation of composite CdS/CdSe nanoparticles. It has been shown that slow interaction of adsorbed selenosulfate with surface-trapped CdS conduction band electrons is the limiting stage of the photocatalytic reaction.     

Structure-property correlation of CdSe clusters using experimental results and first-principles DFT calculations

Structures and properties of CdSe quantum dots (clusters) up to a diameter of approximately 2 nm were investigated by combining experimental absorption, photoluminescence (PL), and X-ray diffraction (XRD) spectroscopies as well as ab initio DFT calculations. These CdSe clusters were nucleated and grown from solutions containing respective cadmium and selenium precursors following the hot-injection technique that allows one to obtain size-controlled CdSe clusters having PL efficiency up to 0.5. The DFT calculations were performed at the B3LYP/Lanl2dz level and followed by time-dependent TDDFT calculations to estimate n energy singlet transitions. On the basis of the results of these experimental and theoretical studies, an approach to determine whether the proposed cluster with a mean diameter of approximately 2 nm is more physically reasonable is discussed. It was shown that the minimum nucleus of a CdSe cluster consists of (CdSe)(3) with a six-membered ring and planar structure. No PL is observed for this structure. The formation of the next stable cluster depends on whether hexadecylamine (HDA) was used for the growth of the CdSe clusters. In the absence of HDA, the second cluster was found to be (CdSe)(6) characterized by a broad PL spectrum, while in the presence of HDA, it was found to be (CdSe)(n) (where n > or = 14) with a sharp PL spectrum.     

Template-directed adsorption of block copolymers on alkanethiol-patterned gold surfaces

Functionalized alkanethiols have been self-assembled on gold to modify the wetting properties of the surface and promote or hinder the adsorption of block copolymers containing both hydrophobic and hydrophilic blocks. X-ray photoelectron spectroscopy (XPS) studies of spin-coated polyethylene-block-poly(ethylene oxide) (PE-b-PEO) copolymers on 16-mercaptohexadecanoic acid (MHDA)-, octadecanethiol (ODT)-, and 1H,1H,2H,2H-perfluorodecanethiol (PFDT)-covered surfaces have been performed. In the case of an 80 wt % PEO block copolymer, spin-coating on a gold surface precovered with MHDA results in a polymer film thick enough to completely attenuate Au 4f photoelectrons; spin-coating on the more hydrophobic ODT and PFDT monolayers leads to significantly thinner polymer films and incomplete attenuation of the gold photoelectrons. The opposite results are observed when a 20 wt % PEO block copolymer is used. Angle-resolved XPS studies of the 80 wt % PEO block copolymer spin-coated onto an MHDA-covered surface indicate that the PE blocks of the polymer segregate to the near-surface region, oriented away from the hydrophilic carboxylic acid tails of the monolayers; the surface concentration of PE is further enhanced by annealing at 90 degrees C. Microcontact printing and dip-pen nanolithography have been used to pattern gold surfaces with MHDA, and the surfaces have been backfilled with ODT or PFDT, such that the unpatterned regions of the surface are covered with hydrophobic monolayers. In the case of backfilling with PFDT, spin-coating the 80 wt % PEO copolymer onto these patterned surfaces and subsequent annealing results in the block copolymer preferentially adsorbing on the MHDA-covered regions and forming well-defined patterns that mimic the MHDA pattern, as determined by scanning electron microscopy and atomic force microscopy. Significantly worse patterning, characterized by micron-sized polymer droplets, results when the surface is backfilled with ODT instead of PFDT. Using PFDT and MHDA, polymer features having widths as small as 500 nm have been formed. These studies demonstrate a novel method to pattern block copolymers with nanoscale resolution.     

Photorefractive performance of a CdSe/ZnS core/shell nanoparticle-sensitized polymer

We report the photorefractive performance of a polymer composite sensitized by CdSe/ZnS core/shell nanoparticles, and also comprising poly(N-vinylcarbazole) and an electro-optic chromophore. The nanoparticles are characterized by absorption and photoluminescence spectroscopy, elemental analysis, transmission electron microscopy, and powder x-ray diffraction. The electro-optic response of the composite is measured independently of the photorefractive effect by transmission ellipsometry. An asymmetric two-beam coupling gain of 30.6+/-0.4 cm(-1) is obtained, confirming photorefractivity. Degenerate four-wave mixing is used to assess photorefractive performance and, at a poling field of 70 V microm(-1), yields a diffraction efficiency of 4.21%+/-0.03%, a holographic contrast of 3.05 x 10(-4)+/-1 x 10(-6), a space-charge rise time of 25+/-2 s, and a sensitivity of 4.7 x 10(-5)+/-4 x 10(-6) cm3 J(-1). These results constitute a significant improvement on the performance of previous nanoparticle-sensitized photorefractive polymer composites.     

Synthesis and surface structure of thymine-functionalized, self-assembled monolayer-protected gold nanoparticles

Thymine-functionalized SAM-protected gold nanoparticles with diameters of 2.2 +/- 0.3 nm and 7.0 +/- 1.0 nm were prepared via a modified two-phase transfer method. UV-vis spectra showed that particle size and solvent type, as well as surface charge, influenced the gold surface plasmon band absorption, along with the interaction between thymine terminal groups in the solution. Although the bulky thymine end groups interacted strongly on the particle surface, a well-ordered monolayer of thyminethiol derivatives with a long hydrocarbon chain was formed on the particle surface, exhibiting an ordered, all-trans conformation of the methylene backbone, similar to those of corresponding self-assembled monolayers (SAMs) generated from normal alkanethiols. A larger particle size and a longer reaction time facilitated the formation of more ordered thymine-terminated thiol SAMs. Thermal analysis indicated that reorientation of the SAMs during heat treatment occurred by two processes, caused possibly by the separate recrystallization of the hydrocarbon long chains and thymine units. More ordered SAMs with a higher thermal stability were formed on the larger particle surfaces when compared with those on the smaller ones. A greater density of molecular packing was found on the smaller particle surfaces. However, SAMs formed on the larger gold particles resembled 2D SAMs on the smooth, flat gold surfaces. XPS results confirmed the thymine structure as well as the chemical bond between gold and sulfur. One type of adsorbed sulfur species was observed for the smaller particles and two for the larger ones, but a slightly higher binding energy of thiolate was found for the smaller ones.     

In situ AFM studies on self-assembled monolayers of adsorbed surfactant molecules on well-defined H-terminated Si(111) surfaces in aqueous solutions

The formation of self-assembled monolayers (SAMs) of adsorbed cationic or anionic surfactant molecules on atomically flat H-terminated Si(111) surfaces in aqueous solutions was investigated by in situ AFM measurements, using octyl trimethylammonium chloride (C8TAC), dodecyl trimethylammonium chloride (C12TAC), octadecyl trimethylammonium chloride (C18TAC)) sodium dodecyl sulfate (STS), and sodium tetradecyl sulfate (SDS). The adsorbed surfactant layer with well-ordered molecular arrangement was formed when the Si(111) surface was in contact with 1.0x10(-4) M C18TAC, whereas a slightly roughened layer was formed for 1.0x10(-4) M C8TAC and C12TAC. On the other hand, the addition of alcohols to solutions of 1.0x10(-4) M C8TAC, C12TAC, or SDS improved the molecular arrangement in the adsorbed surfactant layer. Similarly, the addition of a salt, KCl, also improved the molecular arrangement for both the cationic and anionic surfactant layers. Moreover, the adsorbed surfactant layer with a well-ordered structure was formed in a solution of mixed cationic (C12TAC) and anionic (SDS) surfactants, though each surfactant alone did not form the well-ordered layer. These results were all explained by taking into account electrostatic repulsion between ionic head groups of adsorbed surfactant molecules as well as hydrophobic interaction between their alkyl chains, which increases with the increasing chain length, together with the increase in the hydrophobic interaction or the decrease in the electrostatic repulsion by incorporating alcohol molecules into the adsorbed surfactant layer, the decrease in the electrostatic repulsion by increasing the concentration of counterions, and the decrease in the electrostatic repulsion by alternate arrangement of cationic and anionic surfactant molecules. The present results have revealed various factors to form the well-ordered adsorbed surfactant layers on the H-Si(111) surface, which have a possibility of realizing the third generation surfaces with flexible structures and functions easily adaptable to circumstances.     

Investigation of dynamics of radiolytic formation of CdSe nanoparticles in aqueous solutions

The formation of cadmium selenide, CdSe, nanoparticles in aqueous solutions containing equimolar ammoniated cadmium sulfate, [Cd(NH(3))](4)SO(4) and sodium selenosulfate, Na(2)SeSO(3) as the starting materials, has been investigated by electron pulse radiolysis coupled with kinetic spectrometry. The formation of CdSe nanoparticles was found to proceed through the generation of short-lived transient intermediate species having an absorption peak at 520 nm, which is formed only upon the reaction of hydrated electrons, e(aq) with the precursor ions under deaerated conditions. The transient intermediate species decays with a weighted average rate constant, 1.2 × 10(7) s(-1). The transient intermediate species formed in the case of individual precursors did not match with the transients formed when both the precursors are taken together in the solutions under the present experimental conditions. The reaction rate constants between the precursor ions, [Cd(NH(3))(4)](2+) and the transient intermediate species formed from [SeSO(3)](2-) was 1.9 × 10(10) M(-1) s(-1). Similarly, the reaction rate constants between the precursor ions, [SeSO(3)](2-) and the transient intermediate species formed from [Cd(NH(3))(4)](2+) was 5.5 × 10(10) M(-1) s(-1). This clearly indicates that the formation of CdSe nanoparticles occurs through both reaction channels. However, the major reaction channel is through the reaction of e(aq) with the [Cd(NH(3))(4)](2+) ions (k = 3.1 × 10 (10) M(-1) s(-1)), as its rate constant is one order higher than that of the reaction of e(aq) with the [SeSO(3)](2-) ions (k = 2.3 × 10(9) M(-1) s(-1)).     

Strong resistance of a thin crystalline layer of balanced charged groups to protein adsorption

Resistance of mixed self-assembled monolayers (SAMs) with various counter-charged terminal groups of different valence and protonation/deprotonation states to nonspecific protein adsorption is investigated. It is demonstrated that excellent nonfouling surfaces can be readily constructed from mixed positively and negatively charged components of equal valence in a wide range of thiol solution compositions. Furthermore, the lattice structure of one of the mixed SAM systems studied is revealed by atomic force microscopy (AFM) to be (5.2 +/- 0.2 A x 5.2 +/- 0.2 A)60 degrees . Results indicate that the packing structure of mixed charged SAMs is determined by strong charge-charge interactions of the terminal groups rather than S-Au and chain-chain interactions. This work provides direct evidence that conformational flexibility is not required for protein resistance of a surface and even a single compact layer of charged groups of balanced charge with a crystalline structure can resist nonspecific protein adsorption, suggesting that tightly bound water molecules on the topmost part of the mixed SAMs play a dominant role in surface resistance to nonspecific protein adsorption.     

Free radical sensor based on CdSe quantum dots with added 4-amino-2,2,6,6-tetramethylpiperidine oxide functionality

The association and resulting fluorescence quenching of CdSe quantum dots by 4-amino-2,2,6,6-tetramethylpiperidine oxide (4-amino-TEMPO), a persistent nitroxide, have been examined using electron paramagnetic resonance (EPR) and fluorescence spectroscopy. EPR data suggest binding constants around (8 +/- 4) x 10(6) M(-1) for green (2.4-2.5 nm) nanoparticles, and the application of Job's method indicates that the preferred mode of binding involves one or two quencher molecules per quantum dot, although more quenchers could bind at high concentrations of 4-amino-TEMPO. Fluorescence quenching by 4-amino-TEMPO is at least 3 orders of magnitude more efficient than by TEMPO itself, reflecting the strong binding confirmed by the EPR data. Stern-Volmer plots are nonlinear and in light of the EPR data probably reflect ready accessibility of the CdSe surface to one or two 4-amino-TEMPO molecules, while additional quenchers can only bind if they displace trioctylphosphine oxide ligands. Quantum dot-4-amino-TEMPO complexes can be used as free radical sensors, since the fluorescence (quenched by the nitroxide) is readily restored when radicals are trapped to form alkoxyamines.     

Planar polarized light emission from CdSe nanoparticle clusters

This paper describes synthesis and optical properties of planar clusters of CdSe nanocrystals. The clusters emit linearly polarized light in the plane of the cluster. The emission wavelength of the clusters can be adjusted between 568 and 639 nm with the size of the CdSe nanocrystals. Planar CdSe microclusters were synthesized by reaction of trioctylphosphine oxide-coated CdSe/CdS nanocrystals with 3-aminopropylsilyl-modified Ca(2)Nb(3)O(10) nanosheets in THF. The clusters are 3.92 +/- 1.18 mum length/width and 91 +/- 37 nm thickness, and they consist of alternating layers of Ca(2)Nb(3)O(10) to which CdSe nanocrystals are attached with densities of 5300 +/-310 particles per side of a single Ca(2)Nb(3)O(10) sheet. The chemical inertness of the clusters in coordinating solvents suggests covalent interactions between the aminopropyl groups and CdSe nanocrystals. Upon excitation at lambda(exc) = 400 nm, the clusters emit green (568 nm), orange (589 nm), or red (639 nm) light, depending on the size of the CdSe crystals. The light is emitted preferentially in the cluster plane and it is linearly polarized along the cluster edges. Combined fluorescence microscopy and atomic force microscopy reveal that the directional emission efficiency depends linearly on the thickness of the clusters, which varies between 70 and 180 nm. The ability to manipulate the direction and polarization of the photoemission of CdSe nanoparticles via assembly into 2D structures is of interest for applications of these and similar structures in advanced optical materials and devices.     

A tripodal [2]rotaxane on the surface of gold

Tripodal [2]rotaxane, 3, and the structurally related axle, 2, incorporating a viologen moiety, a crown ether, and three thiol anchoring groups have been synthesized. Analogous monopodal derivatives, 1, have also been prepared. Self-assembled monolayers of the above tripodal and monopodal systems on gold have been studied by cyclic voltammetry. It has been shown that a thiol anchoring group is required to attach the monopodal viologen 1 to the surface of gold and that the maximum surface coverage of 1 corresponds to 2.7 x 10(-10) mol.cm(-2). The adsorbed monopodal viologen 1 does not thread bis-p-phenylene-34-crown-10 ether, 6. However, the tripodal axle 2 adsorbed on the surface of gold threads the crown ether 6 to form a hetero [2]rotaxane. In the case of the tripodal axle 2, the surface coverage is 7 x 10(-11) mol.cm(-2), while for the tripodal [2]rotaxane 3 the surface coverage reaches 1.1 x 10(-10) mol.cm(-2).     

Preparation and stability of strongly luminescent CdSe/Cd(OH)<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> nanocomposite particles in aqueous solution

Cadmium hydroxide-deposited cadmium selenide nanoparticles were prepared by the addition of cadmium sulfate solution to cadmium selenide nanoparticles in a weak alkaline solution at room temperature. The photoluminescence measurements displayed that the luminescence intensity was greatly increased by the addition of cadmium ions due to the formation of cadmium hydroxide on the surfaces of the cadmium selenide nanoparticles. Then, CdSe/Cd(OH)₂/SiO₂ nanocomposite particles were synthesized using 3-mercatopropyl trimethoxysilane by Stöber method. After the formation of CdSe/Cd(OH)₂/SiO₂ nanocomposite particles, the emission ability was mostly stabilized. Additionally, the stabilization of the composite particles against dilution with the physiological saline was checked. The results showed that the photoluminescence stability was promoted after the deposition of silica on the surfaces of the CdSe/Cd(OH)₂ nanoparticles. Comparison of the stability of CdSe/SiO₂ nanoparticles with that of CdSe/Cd(OH)₂/SiO₂ ones showed that Cd(OH)₂ shell could enhance the photoluminescence effectively.     

Properties of the CdSe(0001), (0001), and (1120) single crystal surfaces: Relaxation, reconstruction, and adatom and admolecule adsorption

Details of the chemical mechanism underlying the growth of colloidal semiconductor nanocrystals remain poorly understood. To provide insight into the subject, we have preformed a comprehensive study of the polar (0001) and (0001) and nonpolar (1120) wurtzite CdSe surfaces that are exposed during crystal growth using first-principles density functional theory (DFT-GGA) calculations. Stabilization of these surfaces by relaxation and reconstruction was considered. Two particular reconstructions of the polar surfaces were examined: vacancy formation on a 2 x 2 unit cell and addition of Se and Cd atoms on the (0001) and (0001) surfaces, respectively. Calculation results indicate that the (1120) is the most stable surface when compared to the two polar surfaces. Furthermore, reconstructions of the (0001) surface are energetically favored when compared to reconstructions of the (0001) facet. Adsorption of Cd and Se atoms and the CdSe molecule on the three relaxed surfaces and two reconstructed (0001) surfaces were also investigated. Several binding sites were considered to determine the most stable binding geometries and energetics. Atomic species preferentially bind in either 2-fold or 3-fold sites, while the CdSe molecule binds parallel to the surface on all of the considered surfaces. Vibrational frequencies of the adspecies were calculated for the most stable binding configurations and were included in the zero point energy correction. Diffusion barriers for the atomic and molecular species were estimated where possible to be between 0.2 and 0.4 eV on the three relaxed surfaces. Thermochemistry of the CdSe molecule binding and dissociation was also investigated. On all considered surfaces, dissociation is preferred to desorption with dissociation only exothermic on the (0001) surface. Comparison of the three relaxed and two reconstructed surfaces indicates that CdSe molecule binding and dissociation is thermodynamically favored on the (0001) surface. This implies that under a reaction-controlled regime, the rate of homoepitaxy would be faster on the (0001) Se terminated surface than on the (0001) and (1120) surfaces, making the (0001) surface of a nanocrystal the primary direction of growth.     

Multidentate surface ligand exchange for the immobilization of CdSe/ZnS quantum dots and surface quantum dot-oligonucleotide conjugates

A method for synthesizing multidentate thiol ligands on fused silica surfaces (e.g., optical fibers) was developed for the immobilization of CdSe/ZnS quantum dots (QDs) capped with hydrophilic or hydrophobic ligands. This work was motivated by the poor stability of QDs immobilized via monodentate thiol ligands and the need for stable immobilization strategies in the development of sensor technologies based on QDs. Multi-dentate immobilization was able to withstand washing protocols, and surface ligand exchange occurred via self-assembly through the zinc-metal affinity interaction. Atomic force and scanning electron microscopy images suggested that the QDs were immobilized at high density, approximately 2-4 x 10 (13) cm (-2). It was possible to immobilize one, two, or three colors of QD. Upon immobilization, 1-2 nm bathochromic shifts in the PL spectra were observed. This was attributed to both ligand exchange and the change in local environment. The change in environment was accompanied by a decrease in PL lifetime. Self-assembly of immobilized QD-oligonucleotide and QD-avidin conjugates was also demonstrated. These conjugates were able to hybridize with complementary oligonucleotide and bind biotin, respectively. This versatile immobilization chemistry is an important step in the development of surface-based QD nanosensors. Such technology requires QDs to be immobilized such that they remain accessible to target molecules in solution.     

Optical method for predicting the composition of self-assembled monolayers of mixed thiols on surfaces coated with silver nanoparticles

With a simple optical method, based on UV-vis absorption spectra on glass slides, it is possible to predict the composition of self-assembled monolayers of mixed thiols, grafted on monolayers of silver nanoparticles. Glass slides are modified with the layer-by-layer technique, first forming a monolayer of mercaptopropyltrimethoxysilane, then grafting a monolayer of silver nanoparticles on it. These surfaces are further coated by single or mixed thiol monolayers, by dipping the slides in toluene solutions of the chosen thiols. Exchange constants are calculated for the competitive deposition between the colorless 1-dodecanethiol or PEG5000 thiol and BDP-SH, with the latter being a thiol-bearing molecule containing the strongly absorbing BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety, synthesized on purpose. The constants are calculated by determining the fraction of BDP-SH deposited on the surface from a solution with a given molar fraction, directly measuring the absorption spectra of BDP-SH on the slides. Then, the exchange constant for the competitive deposition between 1-dodecanethiol and PEG5000 thiol is calculated by combining their exchange constants with BDP-SH. This allows to predict the fraction of the two colorless thiols coating the silver nanoparticles slides obtained from a toluene solution with a given molar fraction, for example, of PEG5000 thiol. The correctness of the calculated surface fraction is verified by studying the coating competition between 1-dodecanethiol and a PEG5000 thiol remotely modified with a strongly absorbing fluorescein fragment.