The erratic emission of pyrene on gold nanoparticles

The Interaction of Amines with Gold Nanoparticles

Understanding the interactions between amines and the surface of gold nanoparticles is important because of their role in the stabilization of the nanosystems, in the formation of the protein corona, and in the preparation of semisynthetic nanozymes. By using fluorescence spectroscopy, electrochemistry, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and molecular simulation, a detailed picture of these interactions is obtained. Herein, it is shown that amines interact with surface Au(0) atoms of the nanoparticles with their lone electron pair with a strength linearly correlating with their basicity corrected for steric hindrance. The kinetics of binding depends on the position of the gold atoms (flat surfaces or edges) while the mode of binding involves a single Au(0) with nitrogen sitting on top of it. A small fraction of surface Au(I) atoms, still present, is reduced by the amines yielding a much stronger Au(0)-RN.+ (RN. , after the loss of a proton) interaction. In this case, the mode of binding involves two Au(0) atoms with a bridging nitrogen placed between them. Stable Au nanoparticles, as those required for robust semisynthetic nanozymes preparation, are better obtained when the protein is involved (at least in part) in the reduction of the gold ions.

Aggregation behaviour of pyrene-based luminescent materials, from molecular design and optical properties to application

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

Luminescent Self-Assembled Monolayer on Gold Nanoparticles: Tuning of Emission According to the Surface Curvature

Until now, the ability to form a self-assembled monolayer (SAM) on a surface has been investigated according to deposition techniques, which in turn depend on surface-coater interactions. In this paper, we pursued two goals: to form a SAM on a gold nanosurface and to correlate its formation to the nanosurface curvature. To achieve these objectives, gold nanoparticles of different shapes (spheres, rods, and triangles) were functionalized with a luminescent thiolated bipyridine (Bpy-SH), and the SAM formation was studied by investigating the photo-physics of Bpy-SH. We have shown that emission wavelength and excited-state lifetime of Bpy-SH are strongly correlated to the formation of specific aggregates within SAMs, the nature of these aggregates being in close correlation to the shape of the nanoparticles. Micro-Raman spectroscopy investigation was used to test the SERS effect of gold nanoparticles on thiolated bipyridine forming SAMs.

Reductive Amination Reaction for the Functionalization of Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) represent intriguing biopolymeric nanocrystalline materials, that are biocompatible, sustainable and renewable, can be chemically functionalized and are endowed with exceptional mechanical properties. Recently, studies have been performed to prepare CNCs with extraordinary photophysical properties, also by means of their functionalization with organic light-emitting fluorophores. In this paper, we used the reductive amination reaction to chemically bind 4-(1-pyrenyl)butanamine selectively to the reducing termini of sulfated or neutral CNCs (S_CNC and N_CNC) obtained from sulfuric acid or hydrochloric acid hydrolysis. The functionalization reaction is simple and straightforward, and it induces the appearance of the typical pyrene emission profile in the functionalized materials. After a characterization of the new materials performed by ATR-FTIR and fluorescence spectroscopies, we demonstrate luminescence quenching of the decorated N_CNC by copper (II) sulfate, hypothesizing for these new functionalized materials an application in water purification technologies.

A Selective Ratiometric Fluorescent Probe for No-Wash Detection of PVC Microplastic

Microplastics (MP) are micrometric plastic particles present in drinking water, food and the environment that constitute an emerging pollutant and pose a menace to human health. Novel methods for the fast detection of these new contaminants are needed. Fluorescence-based detection exploits the use of specific probes to label the MP particles. This method can be environmentally friendly, low-cost, easily scalable but also very sensitive and specific. Here, we present the synthesis and application of a new probe based on perylene-diimide (PDI), which can be prepared in a few minutes by a one-pot reaction using a conventional microwave oven and can be used for the direct detection of MP in water without any further treatment of the sample. The green fluorescence is strongly quenched in water at neutral pH because of the formation dimers. The ability of the probe to label MP was tested for polyvinyl chloride (PVC), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), poly methyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE). The probe showed considerable selectivity to PVC MP, which presented an intense red emission after staining. Interestingly, the fluorescence of the MP after labeling could be detected, under excitation with a blue diode, with a conventional CMOS color camera. Good selectivity was achieved analyzing the red to green fluorescence intensity ratio. UV-Vis absorption, steady-state and time-resolved fluorescence spectroscopy, fluorescence anisotropy, fluorescence wide-field and confocal laser scanning microscopy allowed elucidating the mechanism of the staining in detail.

Pyrene-Terminated Tin Sulfide Clusters: Optical Properties and Deposition on a Metal Surface

Herein, we present the synthesis of two pyrene-functionalized clusters, [(Rpyr Sn)4 S6 ]⋅2 CH2 Cl2 (4) and [(Rpyr Sn)4 Sn2 S10 ]⋅n CH2 Cl2 (n=4, 5 a; n=2, 5 b; Rpyr =CMe2 CH2 C(Me)N-NC(H)C16 H9 ), both of which form in reactions of the organotin sulfide cluster [(RN Sn)4 S6 ] (C; RN =CMe2 CH2 C(Me)N-NH2 ) with the well-known fluorescent dye 1-pyrenecarboxaldehyde (B). In contrast, reactions using an organotin sulfide cluster with another core structure, [(RN Sn)3 S4 Cl] (A), leads to formation of small molecular fragments, [(Rpyr Cl2 Sn)2 S] (1), (pyren-1-ylmethylene)hydrazine (2), and 1,2-bis(pyren-1-ylmethylene)hydrazine (3). Besides synthesis and structures of the new compounds, we report the influence of the inorganic core on the optical properties of the dye, which was analyzed exemplarily for compound 5 a via absorption and fluorescence spectroscopy. This cluster was also used for exploring the potential of such non-volatile clusters for deposition on a metal surface under vacuum conditions.

The nucleobase assisted pyrene functionalization of gold nanoparticles

Gold nanoparticles were functionalized with a pyrene fluorophore without compromising the functional behaviour of the fluorophore.

A quick one-step synthesis of luminescent gold nanospheres

Gold nanospheres, coated with luminescent molecules (1-pyrenemethylamine hydrochloride, fluorescein isothiocyanate or cresyl violet perchlorate), have been synthesized and purified by a fast one-step procedure. Luminescent nanoparticles have been obtained, in which the match of the plasmonic and emissive properties gives nanosized fluorophores useful in different application fields.

Dual emitting Ag35 nanocluster protected by 2-pyrene imine thiol

In this communication, we present the synthesis of 2-pyrene imine thiol (2-PIT)-protected Ag₃₅ nanoclusters using a ligand exchange-induced structural transformation reaction. The formation of the nanocluster and its composition were confirmed through several spectroscopic and electron microscopic studies. The UV-vis absorption spectrum showed a set of characteristic features of the nanocluster. This nanocluster showed blue emission under UV light due to pyrene to metal core charge-transfer, and NIR emission due to charge-transfer within the metal core. This is the first report on dual emitting pyrene protected atomically precise silver nanoclusters.

Study on the Assembly Structure Variation of Cetyltrimethylammonium Bromide on the Surface of Gold Nanoparticles

In this work, the self-assembly behavior of cetyltrimethylammonium bromide (CTAB) on the surface of citrate-capped gold nanoparticles (AuNPs) in solution has been studied by UV-vis absorption spectroscopy, fluorescence probe techniques, ζ potentiometric methods, transmission electron microscopy, etc. The UV-vis spectra show that the color with the increase of CTAB for the mixture containing CTAB and a given amount of AuNPs changes from red to blue and then to red. The absolute value of ζ potential corresponding to this color change decreases initially and then increases. Specially, the reversible color change, from red to blue and then to red, could be observed only in the case of a gradual addition of a AuNP solution to a CTAB solution; however, this reversible change is not suitable for the mixture formed in a reverse order of mixing. The results from pyrene used as the fluorescence probe indicate that the features in the fluorescence spectrum (including fluorescence quenching, I ₁/I ₃, and the excimer) well correspond to those from the UV-vis spectrum mentioned above. Based on the experimental results, the mechanism of the assembly structure variation of CTAB on the surface of negatively charged AuNPs was proposed. For a given amount of AuNPs, the assembly structure of CTAB on the surface of AuNPs undergoes the transformation from a monolayer to a bilayer with the increase of CTAB. In the case of the concentration of CTAB far beyond its critical micelle concentration (CMC) and the higher ratio of CTAB and AuNPs, there is a possibility of the formation of an extra micellar structure only after the formation of a double-layer structure.

Tunable Aminooxy-Functionalized Monolayer-Protected Gold Clusters for Non-Polar or Aqueous Oximation Reactions

Aminooxy (-ONH2) groups are well known for their chemoselective reactions with carbonyl compounds, specifically aldehydes and ketones. The versatility of aminooxy chemistry has proven to be an attractive feature that continues to stimulate new applications. This work describes application of aminooxy 'click chemistry' on the surface of gold nanoparticles. We present here a trifunctional amine-containing aminooxy alkane thiol ligand for use in the functionalization of gold monolayer protected clusters (Au MPCs). Diethanolamine is readily transformed into an organic-soluble aminooxy thiol (AOT) ligand using a short synthetic path. The synthesized AOT ligand was coated on ≤ 2 nm diameter hexanethiolate (C6S)-capped Au MPCs using a ligand exchange protocol to afford organic-soluble AOT/C6S (1:1 ratio) Au mixed monolayer protected clusters (MMPCs). This work describes the synthesis of Au(C6S)(AOT) MMPCs and representative oximation reactions with various types of aldehyde-containing molecules, highlighting the ease and versatility of the chemistry and how amine protonation can be used to switch solubility characteristics.

Self-Assembled Biocompatible Fluorescent Nanoparticles for Bioimaging

Fluorescence is a powerful tool for mapping biological events in real-time with high spatial resolution. Ultra-bright probes are needed in order to achieve high sensitivity: these probes are typically obtained by gathering a huge number of fluorophores in a single nanoparticle (NP). Unfortunately this assembly produces quenching of the fluorescence because of short-range intermolecular interactions. Here we demonstrate that rational structural modification of a well-known molecular fluorophore N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) (NBD) produces fluorophores that self-assemble in nanoparticles in the biocompatible environment without any dramatic decrease of the fluorescence quantum yield. Most importantly, the resulting NP show, in an aqueous environment, a brightness which is more than six orders of magnitude higher than the molecular component in the organic solvent. Moreover, the NP are prepared by nanoprecipitation and they are stabilized only via non-covalent interaction, they are surprisingly stable and can be observed as individual bright spots freely diffusing in solution at a concentration as low as 1 nM. The suitability of the NP as biocompatible fluorescent probes was demonstrated in the case of HeLa cells by fluorescence confocal microscopy and MTS assays.

Towards optimisation of surface enhanced photodynamic therapy of breast cancer cells using gold nanoparticle–photosensitiser conjugates

Surface enhanced fluorescence of zinc pthalocyanine-functionalised gold nanoparticles leads to a remarkable enhancement in photodynamic efficiency and cell death.

Development of pyrene-stacked carbon nanotube-based hybrid: measurement of NO3− ions using fluorescence spectroscopy

CNT@pyrene hybrid for fluorescent recognition of nitrate ions.

Low-Temperature Synthesis of Carbon-Rich Nanoparticles with a Clickable Surface for Functionalization

Carbon nanoparticles (CNPs) are promising materials for optoelectronic and biomedical applications thanks to their optical properties, low production cost, and superior biocompatibility compared to traditional semiconductor quantum dots. The countless synthetic methods reported allow a library of diverse CNP structures and optical properties, guiding their subsequent applications. However, the current drawbacks lie mainly within these synthetic processes, as many of them require harsh conditions preventing control over morphology and often generating chemically inert nanoparticles. Thus, more advances on low temperature and controllable synthetic processes are desirable. In this study, we suggest a new strategy to synthesize CNPs with tunable size, while avoiding the use of harsh conditions and allowing easy surface functionalization. The metastable state of polyyne-containing materials appoints them as ideal precursors for low-temperature preparation of carbon-rich structures. Our approach is to synthesize octatetrayne-containing particles prompt to spontaneous reaction, including topochemical polymerization, followed by aromatization, to avoid harsh carbonization steps. For the particle synthesis, the well-known dispersion polymerization process has been adapted for homocoupling of terminal butadiynes, generating the octatetrayne-containing particles. The method was proven reproducible, scalable, and versatile, as the particles' size can be modulated between 50 and 170 nm. Surface functionalization via thiol-yne click chemistry was completed with a pyrene-modified thiol ligand to provide the CNPs with photoactive properties in the visible range. The functionalized particles exhibit fluorescence at 470 nm arising from excimer formation.

Enhanced luminescence of Au22(SG)18 nanoclusters via rational surface engineering

We report design strategies for the preparation of highly luminescent Au₂₂(SG)₁₈ clusters, where SG is glutathione, by the functionalization of the cluster shell. In these strategies, the cluster shell was covalently modified with small aromatic molecules and pyrene chromophores that led to a 5-fold PL enhancement by rigidifying the shell-gold. Highly luminescent water-soluble gold clusters with a PL quantum yield of 30% were obtained at room temperature. To further enhance the luminescence, the pyrene chromophores in the functionalized Au₂₂ clusters were photoexcited at 350 nm to induce energy transfer from pyrene to the Au₂₂ cluster. Steady-state and time-resolved PL measurements have shown evidence of enhanced rigidity with increased PL lifetimes for the functionalized Au₂₂ clusters. However, the energy transfer efficiency was found to be only 14% because of the competing electron transfer deactivation pathway as evidenced by the formation of the pyrene anion radical revealed in the ultrafast transient absorption measurements. To suppress the electron transfer pathway, the pyrene functionalized Au₂₂ clusters were ion-paired with tetraoctylammonium (TOA) cations that could break the electron transfer pathway, leading to a dramatic 37-fold increase in PL brightness with the resonance energy transfer efficiency of ca. 80%. This work presents effective design strategies for the preparation of highly luminescent gold clusters by the combination of rigidifying effect and energy transfer sensitization.

Dual emission from 2-(4'-N,N-dimethylaminophenyl)pyridoimidazole-nanoparticle composite: effect of β-cyclodextrin

The interactions of the silver nanoparticles with 2-(4'-N,N-dimethylaminophenyl)benzimidazole and its nitrogen substituted analogues, 2-(4'-N,N-dimethylaminophenyl)pyridoimidazoles are investigated by absorption, steady-state and time resolved fluorescence, field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) techniques. The surface plasmon resonance band, the FESEM and the TEM images of the particles suggest that the fluorophores can stabilize the nanoparticles even in the absence of any other stabilizing agent. On the other hand, in the absence of fluorophores the nanoparticles are unstable and coagulate. In contrary to the earlier literature reports that interactions of nanoparticles with intramolecular charge transfer (ICT) or twisted intramolecular charge transfer (TICT) species quenches their fluorescence, to the best of our knowledge, the first ever formation of TICT state by interactions of nanoparticles with the fluorophores is observed. The formation of TICT state in 2-(4'-N,N-dimethylaminophenyl)pyridoimidazoles results in dual emission. The TICT emissions from the nanoparticle-fluorophore complexes are weak. But the emissions become prominent upon complexation with β-cyclodextrin.

Dye-doped silica nanoparticles as luminescent organized systems for nanomedicine

This review summarizes developments and applications of luminescent dye doped silica nanoparticles as versatile organized systems for nanomedicine.

UV/vis and NIR light-responsive spiropyran self-assembled monolayers

Self-assembled monolayers of a 6-nitro BIPS spiropyran (SP) modified with a disulfide-terminated aliphatic chain were prepared on polycrystalline gold surfaces and characterized by UV/vis absorption, surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopies (XPS). The SAMs obtained are composed of the ring-closed form (i.e., spiropyran) only. Irradiation with UV light results in conversion of the monolayer to the merocyanine form (MC), manifested in the appearance of an N(+) contribution in the N 1s region of the XPS spectrum of the SAMs, the characteristic absorption band of the MC form in the visible region at 555 nm, and the C-O stretching band in the SERS spectrum. Recovery of the initial state of the monolayer was observed both thermally and after irradiation with visible light. Several switching cycles were performed and monitored by SERS spectroscopy, demonstrating the stability of the SAMs during repeated switching between SP and MC states. A key finding in the present study is that ring-opening of the surface-immobilized spiropyrans can be induced by irradiation with continuous wave NIR (785 nm) light as well as by irradiation with UV light. We demonstrate that ring-opening by irradiation at 785 nm proceeds by a two-photon absorption pathway both in the SAMs and in the solid state. Hence, spiropyran SAMs on gold can undergo reversible photochemical switching from the SP to the MC form with both UV and NIR and the reverse reaction induced by irradiation with visible light or heating. Furthermore, the observation of NIR-induced switching with a continuous wave source holds important consequences in the study of photochromic switches on surfaces using SERS and emphasizes the importance of the use of multiple complementary techniques in characterizing photoresponsive SAMs.

Luminescence enhancement of pyrene/dispersant nanoarrays driven by the nanoscale spatial effect on mixing

This work presents a simple method to generate ordered chromophore/dispersant nanoarrays through a pore-filling process for a nanoporous polymer template to enhance chromophore luminescence. Fluorescence results combining with the morphological evolution examined by scanning probe microscopy reveal that the enhanced luminescence intensity reaches the maximum intensity as the nanopores of the template are completely filled by the chromophore/dispersant mixture. The variation is attributed to nanoscale spatial effect on the enhanced mixing efficiency of chromophore and dispersant, that is, the alleviation of self-quenching problem, as evidenced by the results of attenuated total reflection Fourier transform IR spectroscopy combining with grazing incident wide-angle X-ray diffraction. The enhanced luminescence of the chromophore/dispersant nanoarrays driven by the nanoscale spatial effect is highly promising for use in designing luminescent nanodevices.

Gold nanoparticles functionalized with deep-cavity cavitands: synthesis, characterization, and photophysical studies

In this report, we present methods of functionalization of AuNP's with deep-cavity cavitands that can include organic molecules. Two types of deep-cavity cavitand-functionalized AuNP's have been synthesized and characterized, one soluble in organic solvents and the other in water. Functionalized AuNP soluble in organic solvents forms a 1:1 host-guest complex where the guest is exposed to the exterior solvents. The one soluble in water forms a 2:1 host-guest complex where the guest is protected from solvent water. Phosphorescence from thiones and benzil included within heterocapsules attached to AuNP was quenched by gold atoms present closer to the guests included within deep-cavity cavitands. During this investigation, we have synthesized four new deep-cavity cavitands. Of these, two thiol-functionalized hosts allowed us to make stable AuNP's. However, AuNP's protected with two amine-functionalized cavitands tended to aggregate within a day.

Tuning the photophysical properties of pyrene-based systems: a theoretical study

Recently new molecular systems based on the pyrene moiety were developed for photovoltaic applications. Here we present the results of a quantum chemical study focused on the effects induced by some different substituents on the electronic properties of pyrene, to obtain general hints for the molecular design of new pyrene-based systems. In particular, a series of electron-donating (hydroxy, amino, acetylamino) and electron-withdrawing (cyano, carbamoyl, formyl, ethynyl, ethenyl) groups were considered. Furthermore, in addition to the single pyrene molecule, two pyrene units linked by ethenylene, ethynylene, 2,5-thienylene, and ethynylene-p-phenylene containing chains of different lengths were taken into account. For all of the model structures presented, the ground state geometries have been optimized using the density functional approach, while the vertical transition energies were calculated using the time-dependent density functional theory. We will show that the tuning of the lowest electronic excitation energy (i.e., the HOMO-LUMO energy gap) as well as the localization of the spatial distributions of the frontier molecular orbitals (i.e., the nature of the electron-hole pair, generated by photon absorption) can be obtained through the analysis of the pyrene frontier molecular orbitals. This approach allows to evaluate the most suitable position of the substituents on the pyrene moiety giving rise to enhanced electronic effects also in function of their electronic nature. In this way, pyrene-structures with tailored electronic properties could be modeled. Our screening shows that promising candidates for photovoltaic applications could be molecular structures formed by two pyrene units joined/linked by a short conjugated bridge containing double or triple bonds (henceforth pyrene-linked dimers). As far as the single pyrene units are considered, the most significant reduction of the transition energy of the lowest optical electronic excitation is obtained with disubstituted pyrenes with push-pull character.

Kinetics study of the binding of multivalent ligands on size-selected gold nanoparticles

The effect of ligand multivalency and nanoparticle size on the binding kinetics of thiol ligands on gold nanoparticles is investigated by exchanging monovalently bound pyrene on gold nanoparticles against flexible mono- and multivalent thiol ligands. Variable-sized gold nanoparticles of 2.2 ± 0.4, 3.2 ± 0.7, and 4.4 ± 0.9 nm diameter are used as substrates. The particles are coated by thiol functionalized pyrene ligands and the binding kinetics of the thiol ligands is studied by time-resolved fluorescence spectroscopy. The effect of multivalency on the binding kinetics is evaluated by comparing the rate constants of ligands of different valency. This comparison reveals that the multivalent ligands are exchanging substantially more rapidly than the monovalent ones. A particle size dependence of the rate constants is also observed, which is used to derive structural information on the binding of the mono- and multivalent ligands to the nanoparticle surface.

Organic polyaromatic hydrocarbons as sensitizing model dyes for semiconductor nanoparticles

The study of interfacial charge-transfer processes (sensitization) of a dye bound to large-bandgap nanostructured metal oxide semiconductors, including TiO(2), ZnO, and SnO(2), is continuing to attract interest in various areas of renewable energy, especially for the development of dye-sensitized solar cells (DSSCs). The scope of this Review is to describe how selected model sensitizers prepared from organic polyaromatic hydrocarbons have been used over the past 15 years to elucidate, through a variety of techniques, fundamental aspects of heterogeneous charge transfer at the surface of a semiconductor. This Review does not focus on the most recent or efficient dyes, but rather on how model dyes prepared from aromatic hydrocarbons have been used, over time, in key fundamental studies of heterogeneous charge transfer. In particular, we describe model chromophores prepared from anthracene, pyrene, perylene, and azulene. As the level of complexity of the model dye-bridge-anchor group compounds has increased, the understanding of some aspects of very complex charge transfer events has improved. The knowledge acquired from the study of the described model dyes is of importance not only for DSSC development but also to other fields of science for which electronic processes at the molecule/semiconductor interface are relevant.

Thermoreversible covalent self-assembly of oligo(p-phenylenevinylene) bridged gold nanoparticles

Organic-inorganic hybrids have been fabricated through mild Diels-Alder cross-linking between maleimide bearing oligo(p-phenylenevinylene) (OPV) and furan functionalized gold nanoparticles with diameter smaller than 2 nm. The OPV ligands afford strong reaction ability toward furan group due to their maleimide moieties. These small gold nanoparticles form close-packed homogeneous hybrids with well-defined interfaces by incorporating OPV ligands in solutions. Covalent assembly and disassembly of gold nanoparticles can be achieved by repeated thermal stimuli on as-obtained hybrids, which can be monitored by fluorescence changes of OPVs and surface plasmon resonance absorption. Moreover, the dramatic photophysical properties and assembly behavior of these hybrids allow this procedure to be performed as a smart assay for monitoring the process of the Diels-Alder reaction.

Photocatalytic coalescence of functionalized gold nanoparticles

A novel strategy for the synthesis of chromophore-functionalized AuNPs with a narrow size distribution is reported. It consists of increasing the size of preprepared NPs by means of a fast (second scale) and clean (light and an organic photocatalyst) method. The results agree with thiolate ligand liberation from the NP surface promoted by photogenerated radicals. This lets gold cores come together and finally coalesce.