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We report the synthesis, characterization, and organic light-emitting diode (OLED) application of the first example of a platinum poly-yne (NPtAP) featuring N-heterocyclic carbene (NHC) ligands. NP...

This study probes femto- and picosecond excited-state dynamics of a series of N-heterocyclic carbene (NHC) ligand-containing platinum(II) complexes of the type trans-(NHC)2PtII(CC-Ar)2, where CC-Ar is an arylacetylide. By using femtosecond transient absorption spectroscopy, two dynamic processes are observed: an ultrafast singlet → triplet intersystem crossing (

Two new platinum(II) compounds with trans-(NHC)2Pt(C≡C–C≡C–R)2 (where NHC = N-heterocyclic carbene and R = phenyl or trimethylsilyl) architecture exhibit sharp blue-green or saturated deep-blue pho...

The control over intermolecular interactions between chromophores at nanomaterial interfaces is important for sensing and light-harvesting applications. To that aim, inorganic nanoparticles with anisotropic shape and surface chemistry can serve as useful supports for organic modification. Herein, novel asymmetric perylene diimides with aspartic acid and oleyl terminal groups were grafted to the edges of the layered silicate clay Laponite, a water-dispersible discoidal nanoparticle. The photophysical properties and solvent-dependent self-assembly of the nanoclay-grafted perylenes were investigated, revealing that the polarity of the terminating ligand dictates the aggregation behavior in aqueous solution, where increased water content generally led to the formation of perylene H-aggregates. The anionic basal surface of the nanoclay provided a binding site for a cationic fluorophore, leading to energy transfer from the face-bound donor to the edge-bound perylene acceptor. This study encourages further research on the use of functional ligands for the formation of organic-inorganic hybrids, particularly where inorganic template particles with specific surface chemistry can be exploited to study intermolecular interactions. Overall, these findings should advance further design and implementation of novel semiconducting ligands towards inorganic-organic hybrids, with potential applications in sensing and energy harvesting.

The iron storage protein bacterioferritin (Bfr) binds up to 12 hemes b at specific sites in its protein shell. The heme b can be substituted with the photosensitizer Zn(II)-protoporphyrin IX (ZnPP), and photosensitized reductive iron release from the ferric oxyhydroxide {[FeO(OH)](n)} core inside the ZnPP-Bfr protein shell was demonstrated [Cioloboc, D., et al. (2018) Biomacromolecules 19, 178–187]. This report describes the X-ray crystal structure of ZnPP-Bfr and the effects of loaded iron on the photophysical properties of the ZnPP. The crystal structure of ZnPP-Bfr shows a unique six-coordinate zinc in the ZnPP with two axial methionine sulfur ligands. Steady state and transient ultraviolet–visible absorption and luminescence spectroscopies show that irradiation with light overlapping the Soret absorption causes oxidation of ZnPP to the cation radical ZnPP(•+) only when the ZnPP-Bfr is loaded with [FeO(OH)](n). Femtosecond transient absorption spectroscopy shows that this photooxidation occurs from the singlet excited state ((1)ZnPP*) on the picosecond time scale and is consistent with two oxidizing populations of Fe(3+), which do not appear to involve the ferroxidase center iron. We propose that [FeO(OH)](n) clusters at or near the inner surface of the protein shell are responsible for ZnPP photooxidation. Hopping of the photoinjected electrons through the [FeO(OH)](n) would effectively cause migration of Fe(2+) through the inner cavity to pores where it exits the protein. Reductive iron mobilization is presumed to be a physiological function of Bfrs. The phototriggered Fe(3+) reduction could be used to identify the sites of iron mobilization within the Bfr protein shell.

A family of complexes of the type trans-(NHC)2Pt(C≡C–Ar)2 (NHC = N-heterocyclic carbene and Ar = substituted phenyl or 4-pyridyl) exhibits blue or blue-green phosphorescence. The photoluminescence ...

The quest for efficient solar-to-fuel conversion has led to the development of numerous homogeneous and heterogeneous systems for photochemical stimulation of 2H+ + 2e− → H2. Many such systems consist of a photosensitizer, an H2-evolving catalyst (HEC), and sacrificial electron donor often with an electron relay between photosensitizer and HEC. Colloidal platinum remains a popular HEC. We report here a novel, simple, and high yield synthesis of Pt nanoparticles (Pt NPs) associated with human heavy chain ferritin (Hfn). The formation of the Pt NPs capitalizes on Hfn's native catalysis of autoxidation of Fe(II)(aq) (ferroxidase activity). Fe(II) reduces Pt(II) to Pt(0) and the rapid ferroxidase reaction produces FeO(OH), which associates with and stabilizes the incipient Pt NPs. This Pt/Fe-Hfn efficiently catalyzes photosensitized H2 production when combined with Eosin Y (EY) as photosensitizer and triethanolamine (TEOA) as sacrificial electron donor. With white light irradiation turnover numbers of 300H2 per Pt, 250H2 per EY were achieved. A quantum yield of 18% for H2 production was obtained with 550 nm irradiation. The fluorescence emission of EY is quenched by TEOA but not by Pt/Fe-Hfn. We propose that the photosensitized H2 production from aqueous TEOA, EY, Pt/Fe-Hfn solution occurs via a reductive quenching pathway in which both the singlet and triplet excited states of EY are reduced by TEOA to the anion radical, EY−˙, which in turn transfers electrons to the Pt/Fe-Hfn HEC. Hfn is known to be a remarkably versatile scaffold for incorporation and stabilization of noble metal and semiconductor nanoparticles. Since both EY and Hfn are amenable to scale-up, we envision further refinements to and applications of this photosensitized H2-generating system.

Conjugated polyelectrolytes (CPEs) are a promising class of materials for photovoltaic and sensing applications due to their ability to undergo efficient photoinduced electron transfer (ET). Although water-soluble poly(p-phenylene ethynylene) (PPE) polyelectrolytes have been synthesized for various applications, no reports have clearly revealed the dynamics of the photoinduced ET process and charge transfer state of PPE-type CPE/electron acceptor systems. Herein, we investigated photoinduced ET from a water-soluble PPE based CPE functionalized with alkyl sulfonate (R–SO3−) as side groups to three cationic electron acceptors. Steady-state absorption studies showed a bathochromic shift of the absorption band for all CPE/acceptor mixtures compared to CPE as a result of the suppression of the conformational changes in the polymer caused by the ion–pair interaction. Stern–Volmer (SV) fluorescence quenching studies revealed that all of the cationic electron acceptors efficiently quenched the fluorescence of CPE with SV constants (KSV) in excess of 106 M−1. Picosecond transient absorption (TA) studies of a CPE/methyl viologen mixture revealed the absorption feature of the cation radical state (CPE˙+) of the polyelectrolyte. Kinetic measurements established that the forward electron transfer in the polyelectrolyte/acceptor mixtures occurs with rate constant kf > 1 × 1012 s−1 and the return ET occurs with kb = 3 × 1011 s−1. We also demonstrated that the electron transfer between a PPE-type polyelectrolyte and an acceptor in their assemblies could be modulated by a supramolecular approach, which revealed that the nature of the acceptor–supramolecule host–guest complexes dictates the kinetics of the electron transfer process.

A series of cis-platinum(II) acetylide complexes containing two-photon-absorbing chromophores have been synthesized and characterized to explore the effects of stereochemistry on the nonlinear absorption properties. The molecules feature 4-(phenylethynyl)phenylethynylene (PE2), diphenylaminofluorene (DPAF), and benzothiazolylfluorene (BTF) ligands. The photophysical properties were investigated under one- and two-photon conditions and compared to the known trans analogues via UV-visible absorption, photoluminescence, femtosecond and nanosecond transient absorption (TA), nanosecond z-scan, and femtosecond two-photon absorption (2PA). The bent cis complexes exhibit blue shifts in the absorption, emission, femtosecond, and nanosecond TA spectra along with lower molar extinction coefficients and lower phosphorescence yields relative to the trans complexes suggesting less efficient Pt-induced spin-orbit coupling and intersystem crossing in the cis configuration. The cis chromophores are noncentrosymmetric and therefore show dipolar behavior with a pronounced 2PA in the 0-0 transition of the S0 → S1 band, while the trans complexes show quadrupolar behavior with a forbidden 0-0 transition. In the S0 → Sn region, both cis and trans complexes show intense two-photon-absorption bands (up to 3700 GM by the peak cross section for cis-BTF) which contain a significant contribution from the excited state absorption (S1 → Sn). All six complexes exhibit comparable nonlinear absorption response with a significant contribution from triplet-triplet absorption that slightly favors trans complexes but is more strongly dependent upon the structure of the π-conjugated chromophore.

A series of 11 complexes of the type trans-(NHC)2Pt(CC-Ar)2 (where NHC = N-heterocyclic carbene) have been synthesized and their photophysics characterized. The complexes display moderately efficient deep blue to green phosphorescence from a triplet excited state that is localized mainly in the aryl acetylide ligand (CC-Ar). The emission energy varies with the substituent on CC-Ar, with the highest energy emission for Ar = 4-pyridyl. The emission quantum efficiency and lifetime for the series decreases with increasing emission energy (Eem), and the effect is identified as arising from an increase in the nonradiative decay rate (knr) with Eem. Temperature-dependent emission lifetime studies for three complexes give activation energies for the nonradiative decay process ∼1000 cm-1, and the thermally activated decay process is attributed to crossing to a nonemissive metal-centered (d-d) excited state. At a low temperature, two different emission progressions are observed. Density functional theory calculations suggest that the triplet energy varies with the torsion of the aryl acetylide rings relative to the plane defined by the PtC4 unit (where C = the carbon atoms bonded to Pt). The multiple emission is ascribed to emission from complexes differing with respect to the aryl acetylide ring torsion. Ultrafast transient absorption spectroscopy reveals a fast relaxation (∼5 ps) that may also be due to aryl acetylide ring torsional relaxation in the triplet excited state.

Self-assembly of small molecules through noncovalent interactions into nanoscale architectures has been extensively studied in supramolecular chemistry. However, it is still challenging to develop a biologically inspired self-assembly system that functions in water with complex structure and dynamics by analogy with those found in nature. Here, we report a new water-soluble cationic porphyrin that undergoes adenosine triphosphate (ATP)-templated self-assembly into right-handed double-helical supramolecular structures. Direct observation of the porphyrin-ATP assembly by transmission electron microscopy has been accomplished. The assemblies consist of superhelical fibers with length greater than 1 μm and width ∼46 nm. The chiral superhelical fibers show reversible disassembly to monomers upon hydrolysis of ATP catalyzed by alkaline phosphatase (ALP), and the nanofibers can be re-formed with subsequent addition of ATP. Moreover, transient self-assembly of a chiral double helix is formed when ALP is present to consume ATP.

This paper reports a photophysical investigation of a series of phenylene ethynylene oligomers (OPE) that are end-substituted with a 1,8-naphthalene imide (NI) acceptor. The NI acceptor is attached to the terminus of the OPEs via an ethynylene (-C≡C-) unit that is linked at the 4-position of the NI unit. A series of three oligomers is investigated, OPE1-NI, OPE3-NI, and OPE5-NI, which contain 1, 3, and 5 phenylene ethynylene repeat units, respectively. The properties of the OPEn-NI series are compared to a corresponding set of unsubstituted OPEs, OPE3 and OPE5, which contain 3 and 5 phenylene ethynylene repeats, respectively. The photophysics of all the compounds are interrogated using a variety of techniques including steady-state absorption, steady-state fluorescence, two-photon absorption, time-resolved fluorescence, and transient absorption spectroscopy on femtosecond-to-microsecond time scales. The effect of solvent polarity on the properties of the oligomers is examined. The results show that the NI-substituted oligomers feature a lowest charge transfer (CT) excited state, where the OPE segment acts as the donor and the NI moiety is the acceptor (OPEn•+-NI•-). The absorption spectra in one-photon and two-photon exhibit a clear manifold of absorption features that can be attributed to direct CT absorption. In moderately polar solvents, the emission is dominated by a broad, solvatochromic band that is due to radiative decay from the CT excited state. Ultrafast transient absorption provides evidence for initial population of a locally excited state (LE) which in moderately polar solvents rapidly (∼1 ps) evolves into the CT excited state. The structure, spectroscopy, and dynamics of the CT state are qualitatively similar for OPE3-NI and OPE5-NI, suggesting that delocalization in the OPE segment does not have much effect on the structure or energetics of the CT excited state.

The two-photon absorption properties of anionic poly(phenylene ethynylene)-type conjugated oligo- and polyelectrolytes are studied in molecularly dissolved and aggregated forms in aqueous solution. Several different polyvalent cations are used to induce aggregation. It is found that both materials in the aggregated form exhibit enhanced two-photon excited fluorescence (2PEF) and two-photon cross section (σ2) compared with the molecularly dissolved structures. The 2PEF and σ2 are unaffected by the nature of the polyvalent cation that is used to induce aggregation. The two-photon absorption cross section enhancement arises because of the increase in the difference dipole moment (Δμ) in the aggregates of the conjugated materials, an effect that is attributed to the introduction of charge transfer character into the aggregate excited state.

Silver (AgNPs) and gold (AuNPs) nanoparticles in aqueous solution were generated and stabilized using the 10-oxo-10H-dibenzene thiopyran-3-4-dicarboximide chitosan (TXICh) macrophotoinitiator. The photoinitiator and the nanoparticles in aqueous solution were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). Pure TXICh in aqueous solution forms self-assembled particles with diameter around 30 nm. AgNPs were prepared using TXICh in the presence and absence of triethanolamine (TEOH). During irradiation, a broad band in the range of 410-415 nm was observed, corresponding to the plasmon absorption, indicating the AgNPs formation. TEM images revealed that the AgNPs had spherical shape in the absence and presence of TEOH. The synthesis of AgNPs in the presence of TEOH occurred rapidly (maximum conversion reached after 15 min), whereas in its absence 4 hours were required. The AgNPs prepared with TXICh/TEOH presented smaller and more uniform nanoparticles size. AuNPs were also prepared using TXICh as photoinitiator/stabilizer system. These nanoparticles showed an intense surface plasmon band at 530 nm and the TEM images revealed spherical particles of around 4 nm. These studies indicate that TXICh can act not only as a photoinitiator, but also as a stabilizer in the AgNPs and AuNPs formation.

In the present study, we have attempted to investigate, for the first time, the photophysical behavior of 1,1'-diethyl-2,4'-cyanine (ICY)/clay mineral hybrids in the solid state. The effects promoted by ICY loading and clay type on the spectroscopic properties were studied by UV-vis diffuse reflectance spectroscopy (DR) and different fluorescence techniques. The hybrids were characterized by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). UV-vis-DR revealed the formation of ICY H-aggregates in Wyoming montmorillonite (SWy-1) and Laponite (Lap); however, J-aggregates were predominant for ICY on Arizona (SAz-1) and Barasym (SYn-1) montmorillonites. The formation of J-aggregates was favored on clays with a high layer charge density (SAz-1 and SYn-1). Increasing ICY loading leads to an increase in H-aggregates, which become predominant in all of the samples. The fluorescence spectra of ICY-Lap and ICY-SYn-1 hybrids showed two emissive bands, and they were assigned to the monomeric and J-aggregate species. The fluorescence lifetime showed consistent and distinct values for the two species. The longer fluorescence lifetime can be assigned to the ICY monomers, while the second component has a short lifetime value and may be attributed to J-aggregate emission species. Moreover, confocal fluorescence micrographs showed two different fluorescent domains; monomers (greenish domain) and J-aggregates (orange domain) can be clearly distinguished. For ICY adsorbed on SWy-1 and SAz-1, the intensities of the fluorescence spectra were very low, and it was not possible to measure the fluorescence lifetimes due to high iron content in these clays, which acts as an efficient quencher of the excited singlet state of the dye molecules. XRD and TGA curves showed that the intercalation of ICY into the interlayer regions of SWy-1, SAz-1, and SYn-1 occurred for high dye concentration only. In the case of Laponite, ICY adsorbs on the external surface of the layer. Our studies indicate that the ICY-clays, in particular, ICY-SYn-1 and ICY-Lap, are promising hybrid materials with interesting optical and photophysical properties.

A series of 11 complexes of the type

Films of three polymers, based on ethyl(hydroxyethyl)cellulose functionalized with protonated perichromic dyes, were used for anion sensing. The polymer functionalized with protonated Brooker’s merocyanine acts as a chromogenic/fluorogenic system for the selective detection of cyanide in water. An increase of >28 times was verified for the fluorescence lifetime of the sensing units in the polymer in comparison with protonated Brooker’s merocyanine in water. Moreover, an increase in the p K a values was verified for the sensing units in the polymers. Data suggest that the hydrocarbonic polymeric chains provide an adequate microenvironment to protect the sensing unit from bulk water. The other polymer, functionalized with an iminophenol, also showed high selectivity for cyanide (detection limit = 9.36 × 10 −6 mol L −1 and quantification limit = 3.12 × 10 −5 mol L −1 ). The polymer functionalized with azophenol units is unable for the detection of cyanide, due to the low p K a value verified for its chromogenic units.

Curcumin (CUR) has showed promising photophysical properties regarding to biological and chemical sciences. However, the main barrier for those applications are their low solubility and stability in aqueous solution. The effects of two different clay minerals, the montmorillonite (SWy-2) and the Laponite RD (Lap) nanoclay, on the stabilization of Curcumin were investigated. Their effects were compared with two well-established environments (acidic and neutral aqueous media). CUR/clay hybrids were prepared using a simple and fast method, where CUR solution was added into clay suspensions, to obtain well dispersed hybrids in water. The degradation process of CUR and CUR/clays hybrids was investigated using UV–Vis spectroscopic. For both studied hybrids, the CUR degradation process was suppressed by the presence of the clay particles. Furthermore, the Lap showed a great stabilization effect than SWy-2. This behavior was due to the smaller particle size and higher exfoliation ability of Lap, providing a large surface for CUR adsorption compared to SWy-2. The degradation process of CUR solutions and CUR/clay hybrids was also studied in the presence of light. CUR photodegradation process was faster not only in the aqueous solution but also in the clay suspension compared to those studied in the dark. The presence of clay particles accelerated the photodegradation of CUR due to the products formation in the reactions between CUR and oxygen radicals. Our results showed that the singlet oxygen quantum yield ( Φ Δ ) of CUR were about 59% higher in the clay suspensions than CUR in aqueous solution. Therefore, the formation of CUR/clay hybrids, in particularly with Lap, suppressed the degradation in absence light of CUR and increased the singlet oxygen generation, which makes this hybrids of CUR/clay a promising material to enlarge the application of CUR in the biological sciences.

The preparation and characterization of carbon ceramic electrodes (CCEs) produced by the sol–gel method was reported. Different parameters for the manufacture of CCE were studied. Some factors such as the preparation method, type of precursor and catalyst, directly influence the conductive properties, mechanical and morphological characteristics of CCEs, and these are reflected in their electrochemical response. Such factors were evaluated using a 24 (two factors and four levels) factorial design analyzing the anodic peak currents (Ipa) and the variation of peak potential (ΔEp) responses of the respective cyclic voltammograms in presence of potassium ferrocyanide. Analyzing the set of results obtained from cyclic voltammetry, a higher reversibility was observed for the electrodes prepared by basic catalysis using methyltrimethoxysilicate, MTMS, as Si precursor. It is suggested that the obtained material presents a porous morphological structure, providing higher reversibility and better definition of voltammetric peaks. These electrodes were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XDR).

Montmorillonite/PMMA nanocomposites were obtained by in situ photopolymerization. Methyl methacrylate was photopolymerized in the presence of modified clay minerals using thioxanthone (TX) and ethyl 4-(dimethylamino) benzoate (EDB) as photoinitiating system. The organomontmorillonites (SWy-1-C8-Mt and SWy-1-C16-Mt) were prepared by ion exchange of SW-1 Mt with octyltrimethylammonium bromide (C8) and hexyltrimethylammonium bromide (C16), respectively. X-ray diffraction indicated that clay/PMMA nanocomposites can have intercalated or exfoliated structures, or even a mixture of exfoliated and partially intercalated structure layers. The structure of each particular clay polymer nanocomposite (CPN) depends on the clay mineral loading and the solvent used for the preparation. The molecular weights of the SWy-1-C8/PMMA and SWy-1-C16/PMMA (1.0, 3.0 and 5.0%) obtained by photopolymerization in ethanol, were in the range of 1,000,000 to 3,000,000 D, and in acetonitrile the M w values varied from 220,000 to 270,000 D. Photooxidative degradation of clay/PMMA nanocomposites has been investigated using size exclusion chromatography (SEC). Evidence was found that PMMA and CPN degrade by random chain scissions. The polydispersity increases after irradiation and the degradation rate coefficient for pure PMMA is up to 6 times larger than that for CPN. The effects of the clay mineral content, clay mineral type (clay mineral modified by surfactants with different lengths of alkyl chains) and solvent used for dispersion of organoclay on the photodegradation rate coefficients were also studied. The influence of these parameters on the photodegradation process was statistically evaluated using a two-level factorial design. The importance of the parameters was proved to follow the order: clay mineral content > clay mineral type > solvent. CPN with higher clay mineral loadings showed slower rates of oxidation. The clay mineral stabilizes the polymer against UV irradiation. SWy-1 clay mineral scatters and absorbs the incident light, decreasing the degradation rate of polymer present in the CPN.

The organoclay/poly(methyl methacrylate) (PMMA) nanocomposites were prepared by in situ photopolymerization method using two solvents, ethanol and acetonitrile. The influences of organoclay loading, solvent nature and length of attached surfactant (C8 or C16) on thermal and mechanical properties were studied by thermogravimetric analysis and dynamic mechanical analysis. Alkylammonium surfactants with C8 and C16 chain lengths were evaluated as clay modifiers. All the nanocomposites prepared in acetonitrile exhibited improvement in their thermal stability, mainly due to the interaction between the clay and the polymer which is maximized by the exfoliated clay structure. In the case of PMMA and nanocomposites synthesized in ethanol, the thermal stability of polymer and nanocomposites remained practically the same once the clay structure is predominantly of the intercalated type. In comparison with pure PMMA, glass transition temperature and storage modulus of polymer are notably increased by the presence of clay. It was found that the chain length of surfactant attached to the SWy-1 clay affects the Tg values. Glass transition temperatures of nanocomposites SWy-1-C16/PMMA were significantly higher than the values obtained for nanocomposites SWy-1-C8/PMMA. This can be attributed to the modifying agent C16, which has a greater hydrophobic chain length. The organic tail can provide a better dispersion of the MMA monomer in the organoclay, resulting in a nanocomposite with predominant exfoliated structure. Another significant factor to be considered was the effect of solvent used in the nanocomposite preparation. Considering nanocomposites with the same chain length (C8 or C16), Tg values obtained for nanocomposites prepared with ethanol is higher than those observed for those prepared in acetonitrile. This was attributed to the influence of the average molecular weight; once the nanocomposites prepared in ethanol exhibited higher polymeric chains.

In previous works, we have used two-photon induced photochemistry to fabricate 3D microstructures based on proteins, anti-bodies, and enzymes for different types of bio-applications. Among them, we can cite collagen lines to guide the movement of living cells, peptide modified GFP biosensing pads to detect Gram positive bacteria, anti-body pads to determine the type of red blood cells, and trypsin columns in a microfluidic channel to obtain a real time biochemical micro-reactor. In this paper, we report for the first time on two-photon 3D microfabrication of DNA material. We also present our preliminary results on using a commercial 3D printer based on a video projector to polymerize slicing layers of gelatine-objects.

A novel biopolymeric photoinitiator was synthetized from N -phthaloyl chitosan. The 10-oxo-10H-dibenzene thiopyran-3-4-dicarboximide/chitosan (TXICh) structure was characterized by 1D ( 1 H and 13 C) and 2D ( 1 H 1 H COSY, 1 H 13 C HSQC and 1 H 13 C HMBC) NMR experiments. TXICh showed absorption in a wide region of the visible, with bands at 385, 450 and 540 nm. Fluorescence measurements showed three emitting states with lifetimes of 3, 0.612 and 0.021 ns. Transient lifetimes of the same magnitude were found for TXICh by femtosecond time-resolved pump-probe transient absorption spectroscopy. TXICh triplet formation was observed by flash photolysis. This excited state is responsible for producing radicals, which initiate photopolymerization. The efficiency of TXICh as a biopolymeric photoinitiator was checked by photopolymerization kinetics of TEGDMA using photocalorimetry (photo-DSC). The ability and efficiency of TXICh to act as photoinitiator radical in different wavelengths was confirmed.

The dye loading effect on the photophysical behavior of Auramine O adsorbed onto solid clays was studied. When the dye concentration is increased, solid samples of Auramine O incorporated in SYn-1, SAz-1 and SWy-1 clays show an enhancement of the β-band in the UV–vis-DR spectra and the band at 450 nm shifts to the blue. This behavior can be attributed to the formation of H-type dye aggregates. For SYn-1 and SAz-1 clays, which show higher charge density, the formation of H-aggregates of the dye is favored. The fluorescence intensity and lifetime values of AuO decrease with the increasing of dye loading in these clays, since H aggregates do not exhibit fluorescence. The basal spacing of SAz-1 and SYn-1 containing 5% of AuO remains the same as that for pure SAz-1 and SYn-1. The adsorption of the dye predominantly occurs on the external surface of the SAz-1 and SYn-1 clays. On the other hand, for SWy-1 clay, UV–vis results suggest the presence of H- and J- aggregates. The fluorescence emission and lifetimes increase with the AuO concentration. XRD measurements confirm the penetration of the Auramine O into interlayer regions of the SWy-1 clay. When the Auramine is in the interlamellar regions of clay, the rotation of its phenyl rings is restricted, diminishing the internal conversion rate, therefore increasing the emission. The adsorption of the dye occurs on the external surface and in the interlamellar layers of SWy-1.

This paper reports the effect of the SWy-1 montmorillonite content on the kinetic thermal degradation of poly(2-hydroxyethyl methacrylate) (PHEMA)/SWy-1 nanocomposites prepared by in situ photopolymerization, using thermogravimetry analysis (TGA). 2-Hydroxyethyl methacrylate was photopolymerized in the presence of SWy-1 clay mineral using 2-hydroxy-3- (3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N,N-trimethyl-1-propanium chloride (QTX) and triethanolamine as the photoinitiating system. X-Ray diffraction analysis indicates that the PHEMA/SWy-1 nanocomposites present an intercalated structure. The isoconversional Flynn-Wall-Ozawa method was used to estimate activation energies and pre-exponential factors for the thermal decomposition. All nanocomposites exhibited improvement in their thermal stability, mainly due to the large interaction between the PHEMA intercalated in the SWy-1 structure. The activation energies for PHEMA/SWy-1 nanocomposites increased when increasing the clay content. The SWy-1 clay mineral acts as a better insulator, mass transport barrier and as a "crosslinking agent", increasing the activation energies for the decomposition of the polymer present in the nanocomposites.