Langmuir-Blodgett films of 9-phenyl anthracene molecules incorporated into different matrices

This communication reports the surface pressure (pi) versus area per molecule (A) isotherm characteristics of the mixed films of 9-phenyl anthracene (PA) in stearic acid (SA) and polymethyl methacrylate (PMMA) matrices, at the air-water interface. The mixed Langmuir films at the air-water interface have been observed to be easily transferred onto solid substrates to form uniform Langmuir-Blodgett films. By changing various parameters, namely molefraction, surface pressure of lifting and number of layers, the mixed Langmuir-Blodgett (LB) films of various types have been fabricated successfully and their spectroscopic characteristics have been reported. From the isotherm characteristics and the area per molecule versus molefraction plot, it is evident that the PA molecules are successfully incorporated into mixed Langmuir-Blodgett films. UV-vis absorption spectroscopic study of the mixed LB films at various molefractions of PA in two different matrices reveal that formation of I-type aggregate in PMMA matrix whereas both I- and H-type aggregates are playing their dominant role in SA matrix. Moreover, fluorescence spectroscopic study reveals reabsorption effect. Molecular movement persists in the freshly prepared LB films, as is evident from the time dependent changes in both UV-vis absorption and fluorescence spectra of the mixed LB films in both matrices. From our observation it is evident that about 200 h is required to get the LB films in a stable condition. Dimers and higher order n-mers are formed at a higher surface pressure of 30 mNm(-1).     

Studies on the structure and miscibility of mixed Langmuir-Blodgett films of a double-armed dibenzo-18-crown-6 ether with stearic acid

Reported here is the study on the structure of Langmuir-Blodgett (LB) films of double-armed dibenzo-18-crown-6 contain biphenyl (DACE) which are newly synthesized and mixed with stearic acid (SA). In addition, the miscibility of the two compounds was also tested by the measurement of the surface pressure-area (pi-A) isotherms of DACE and DACE/SA with various proportions. It is noted that there is no phase segregation in the mixed monolayer film of DACE/SA. Upon calculation of the excess surface area, it is concluded that the SA molecule can enter into the crown ether ring, while an 18C6 ring can host a maximum of one SA molecule. The difference of spectroscopic properties of DACE in LB films and bulk solution has been investigated by ultraviolet-visible (UV-vis) and Fourier-transfer infrared (FTIR) measurements. Molecules of DACE exist in the mixed LB films as monomers in contrast to those in the concentrated solution as aggregates. The hydrocarbon chains in DACE and DACE/SA LB films are tilted to the normal of the substrate surface, but perpendicular to the dipole moment of CO. Both CO bonds in the phenyl ethers and carboxylic ester of DACE, and the long axes of phenyl rings are aligned nearly perpendicular to the substrate surface. Infrared spectra of mixed LB films of DACE/SA present further evidence that the SA molecules enter into the crown ether rings of DACE.     

Langmuir-Blodgett films of p-terphenyl in different matrices: evidence of dual excimer

Langmuir-Blodgett (LB) films at different mole fractions of p-terphenyl have been prepared using two different matrices, viz., stearic acid (SA) and polymethyl methacrylate (PMMA). Multilayered LB films have been formed by changing various LB parameters namely, mole fraction of mixing, changing the number of layers as well as also the different surface pressure of lifting. The spectroscopic characteristics of mixed LB films, solution and microcrystal have been compared using UV-vis absorption and steady state fluorescence spectroscopy. Change of planarity of TP molecules are occurred while going from solution to solid states/films. Fluorescence spectra of the mixed LB films reveal intense excimeric emission in the mixed LB films with D1 excimer peak at 397 nm and D2 excimer peak at 412 nm. Various LB parameters namely changing the number of layers as well as the different surface pressure of lifting played important roles in the formation of dual excimeric sites in the mixed LB films.     

Surface enhanced resonance Raman scattering imaging of Langmuir-Blodgett monolayers of bis (benzimidazo) thioperylene.

The synthesis, spectroscopic characterization and surface-enhanced spectroscopy of a new electro active organic material bis (benzimidazo) thioperylene (Monothio BZP) are reported. Langmuir monolayers of Monothio BZP were successfully formed on water subphase and characterized by the pi-A surface-pressure area isotherm. Langmuir-Blodgett (LB) monomolecular layers of Monothio BZP were fabricated onto glass substrates and onto silver island films for surface-enhanced spectroscopic studies. The results of surface-enhanced resonance Raman scattering (SERRS), SERRS imaging and surface-enhanced fluorescence (SEF) studies for Monothio BZP LB monolayers are reported. Raman imaging (global imaging and point-by-point mapping) of the SERRS signal for a single monomolecular layer on silver islands were obtained using the 514.5 nm laser line. The SERRS imaging permits a visualization of the variation of the SERRS intensity across of the rough metal surface. The SEF was recorded for the excimer emission of aggregates in the LB film. The distance dependence and the enhancement factor of SEF were determined using fatty acid spacing layers. A temperature dependence study of the LB monolayer SERRS and SEF spectra was carried out between -190 degrees and + 200 degrees C confirming the thermal stability of the LB monolayer on silver. The specificity and the sensitivity of SERRS signal on metal island films was probed using mixed LB films with 0.01% molecular ratio of Monothio BZP in Arachidic Acid (AA). The micro-Raman SERRS spectra from ca. 10(-3) attomole of the dye were recorded.     

Incorporation of ovalbumin within cationic octadecylamine monolayer and a comparative study with zwitterionic DPPC and anionic stearic acid monolayer

In this communication we demonstrated the incorporation of water-soluble surface-active protein OVA within an insoluble cationic ODA monolayer and compared with zwitterionic (DPPC) and anionic (SA) monolayer. The incorporation of OVA is found to be more in ODA as compared to that of DPPC and SA. The kinetics of protein adsorption in lipid monolayer gives the idea that unfolding of OVA is less in case of DPPC than SA and ODA. The pi-A isotherm and compressibility study gives the information about the different states of the protein-lipid mixed monolayer. At higher pressure, OVA tend to squeeze out from the lipids monolayer. High-resolution field emission scanning electron microscope (FE-SEM) images confirm this observation. The surface morphology of DPPC-OVA LB film is far better than ODA-OVA and SA-OVA LB film. OVA forms large irregular aggregates on SA and ODA monolayer. Fluorescence study reveals that protein structure is perturbed more in SA and ODA system compared to that of DPPC. The overall results indicate that DPPC monolayer is better to get protein lipid mixed film than SA and ODA monolayer.     

Langmuir and Langmuir-Blodgett films of N-(4-octadecyloxy-2-hydroxybenzylidene) derivatives of amino acids

Langmuir and Langmuir-Blodgett monolayers of N-(4-octadecyloxy-2-hydroxybenzylidene) derivatives of glycine, tyrosine, and phenylalanine were studied using pi-A isotherms and photoelastic modulated FTIR (PEM-FTIR). Based on compression modulus and interaction parameters, mixed monolayers of these compounds with stearylamine (SAM) showed well-organized monolayers compared to mixed systems with stearic acid (SA) and stearyl alcohol (SAL). The pure amphiphiles exhibited fairly well-ordered packing in the films, and in the mixtures, the ordering increased and showed a triclinic packing arrangement. For the phenylalanine amphiphile the packing showed slight disorder compared to the other two compounds. Surface properties of the LB films of these compounds on solid substrates were analyzed using static and dynamic contact angles of a series of liquids. The surface tension of coated substrates reflected clearly the highly acidic character. Fluidlike monolayers having a molecularly rough surface indicated high wettability for n-alkanes. In contrast, the monolayer containing well-ordered, well-packed alkyl chains indicated low wettability and small hysteresis.     

Photoluminescence of a mixed Langmuir-Blodgett film of C(60) and stearic acid at room temperature

pi-A isotherms, transmission electron microscope (TEM), atomic force microscope (AFM) images and photoluminescence spectra of a mixed Langmuir-Blodgett (LB) film of C(60) and stearic acid (SA) deposited on silicon substrate have been measured at room temperature. C(60)/SA nanoparticles aggregated and formed an ordered net-like structure when deposited on silicon substrate. Two PL intense bands centered at 731 and 806nm, respectively, which are rare at room temperature, were obtained. It is supposed that the particular ordered net-like construction of the LB film plays a crucial role in the enhancement of the photoluminescence. The 731nm PL band is related with the aggregation state of the particles and the 806nm PL band is referred as the intrinsic PL spectrum of the C(60).     

Langmuir-Blodgett thin films of quantum dots: synthesis, surface modification, and fluorescence resonance energy transfer (FRET) studies

We describe herein studies on as-prepared hydrophobic ZnS-CdSe quantum dots (QDs) at the air-water interface. Surface pressure-area (pi-A) isotherms have been used to study the monolayer behavior. Uniform, lamellar multilayer thin films of QDs were deposited by the Langmuir-Blodgett (LB) technique. The role of two different surfactant systems commonly employed in the synthesis of these QDs (trioctylphosphine oxide-octadecylamine (TOPO-ODA) system and trioctylphosphine oxide-tetradecylphosphonic acid (TOPO-TDPA) system) on the monolayer behavior and the quality of thin films produced has been investigated. The thin films were characterized by quartz crystal microgravimetry (QCM), contact angle measurements, fluorescence spectroscopy, and transmission electron microscopy (TEM). These QD films were further modified by an amphiphilic polymer, poly(maleic anhydride-alt-1-tetradecene) (PMA). The hydrophobic interaction between the polymers and the surfactants attached to the QDs drove the self-assembly process. The carboxylic acid functional groups in the polymer were also used to immobilize avidin. We have demonstrated a proof of concept for the biosensing strategy wherein the avidin-coated QD films attracted biotinylated gold nanoparticles, resulting in fluorescence resonance energy transfer (FRET) quenching of the thin films.     

Formation of complex Langmuir and Langmuir-Blodgett films of water soluble rosebengal

This communication reports the formation of complex Langmuir monolayer at the air-water interface by charge transfer types of interaction with the water soluble N-cetyl N,N,N-trimethyl ammonium bromide (CTAB) molecules doped with rosebengal (RB), with the stearic acid (SA) molecules of a preformed SA Langmuir monolayer. The reaction kinetics of the formation of RB-CTAB-SA complex monolayer was monitored by observing the increase in surface pressure with time while the barrier was kept fixed. Completion of interaction kinetics was confirmed by FTIR study. This complex Langmuir films at the air-water interface was transferred onto solid substrates at a desired surface pressure to form multilayered Langmuir-Blodgett films. Spectroscopic characterizations reveal some molecular level interactions as well as formation of microcrystalline aggregates depending upon the molar ratios of CTAB and RB within the complex LB films. Presence of two types of species in the complex LB films was confirmed by fluorescence spectroscopy.     

Interfacial behavior of poly(isoprene-b-methyl methacrylate) diblock copolymers and their blends with polystyrene at the air-water interface

The interfacial behavior of poly(isoprene-b-methyl methacrylate) diblock copolymers (PI-b-PMMA), with similar PMMA blocks but differing in the percentage of PI segments, SP19 (5% PI) and SP38 (52% PI), was studied at the air-water interface. The surface pressure-area (pi-A) isotherms, compression-expansion cycles, and relaxation curves were compared with those of the PMMA homopolymer. The short hydrophobic PI block of SP19 does not contribute to the mean molecular area at low surface pressures and yet has a negative contribution (condensing effect) when the surface pressure increases. On the contrary, the long PI block of SP38 contributes considerably to the surface area from low to high surface pressures. The A-t relaxation curves compare well with those of PMMA at low surface pressures (pi = 2 mN.m-1), but not at intermediate and high pressures (pi = 10, 30 mN.m-1), where a clear dependence on the length of the PI block was observed. The quantitative analysis of the relaxation curves at high pressures shows both a fast and slow component, attributed mostly to the local and middle-to-long-range reorganization of PMMA chains, respectively. PI-b-PMMA diblocks and PMMA were further blended with PS. The PS and PMMA are immiscible at the air-water interface. The addition of PS does not change the pi-A isotherm of PMMA, but the copolymers blended with PS form films that are more condensed at low pressures. The Langmuir-Blodgett (LB) films transferred onto mica substrates were analyzed by atomic force microscopy (AFM). The LB films of single diblocks are uniform, while those of PI-b-PMMA and PMMA blended with PS show aggregates with variable patterns.     

Aggregation behavior of heteroleptic tris(phthalocyaninato) dysprosium complexes with different alkoxy chains in monolayer or multilayer solid films

Three heteroleptic tris(phathlocyaninato) dysprosium triple-decker complexes with different alkoxy groups at the peripheral positions of the medium phthalocyanine ligand (Pc)Dy[Pc(OCnH(2n+1))8]Dy(Pc) (n = 4, 8, 16) (I-III) {Pc = unsubstituted phthalocyaninate; Pc(OC4H9)8 = 2,3,9,10,16,17,23,24-octakis(butyloxy)phthalocyaninate; Pc(OC8H17)8 = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninate; Pc(OC16H33)8 = 2,3,9,10,16,17,23,24-octakis(hexadecyloxy)phthalocyaninate} have been synthesized, and their aggregate behaviors in monolayer and multilayer solid films have been comparatively studied. The pure compounds and their 1:4 mixtures with stearic acid (SA) have been found to form a stable monolayer at the air/water interface with a tilted edge-on orientation of (Pc)Dy[Pc(OCnH(2n+1))8]Dy(Pc) molecules. In the pure monolayers of the three triple-decker compounds, wirelike molecular aggregates were observed by high-resolution transmission electron microscopy (HRTEM). Adding SA has been found to prevent triple-decker compounds (Pc)Dy[Pc(OC4H9)8]Dy(Pc) (I) and (Pc)Dy[Pc(OC8H17)8]Dy(Pc) (II) from forming large aggregates, and small domains with a diameter of ca. 10 nm were observed in the mixed monolayers. HRTEM studies revealed that two crystalline phases with rectangular and hexagonal lattice structure are present in the small domains. However, both pi-A isotherms and HRTEM studies indicated that the mixed monolayer of compound (Pc)Dy[Pc(OC16H33)8]Dy(Pc) (III) with SA did not show a difference from the corresponding pure monolayer. The SA molecules were pressed into the cavity above the phthalocyanine ring formed by the eight long hexadecyloxy side chains of the medium macrocycle ligand in III. The multilayer LB films of all of these triple deckers fabricated by the vertical dipping method showed very good layered structure as revealed by the multiple-order diffraction peaks in low-angle X-ray diffraction (LAXRD) patterns.     

Magnetic Langmuir-Blodgett films of ferritin with different iron contents

Magnetic Langmuir-Blodgett films of four ferritin derivatives with different iron contents containing 4220, 3062, 2200, and 1200 iron atoms, respectively, have been prepared by using the adsorption properties of a 6/1 mixed monolayer of methyl stearate (SME) and dioctadecyldimethylammonium bromide (DODA). The molecular organization of the mixed SME/DODA monolayer is strongly affected by the presence of the water-soluble protein in the subphase as shown by pi-A isotherms, BAM images, and imaging ellipsometry at the water-air interface. BAM images reveal the heterogeneity of this mixed monolayer at the air-water interface. We propose that the ferritin is located under the mixed matrix in those regions where the reflectivity is higher whereas the dark regions correspond to the matrix. Ellipsometric angle measurements performed in zones of different brightness of the mixed monolayer confirm such a heterogeneous distribution of the protein under the lipid matrix. Transfer of the monolayer onto different substrates allowed the preparation of multilayer LB films of ferritin. Both infrared and UV-vis spectroscopy indicate that ferritin molecules are incorporated within the LB films. AFM measurements show that the heterogeneous distribution of the ferritin at the water-air interface is maintained when it is transferred onto solid substrates. Magnetic measurements show that the superparamagnetic properties of these molecules are preserved. Thus, marked hysteresis loops of magnetization are obtained below 20 K with coercive fields that depend on the number of iron atoms of the ferritin derivative.     

组份可控的钌螯合物功能单分子膜

用作“表面离子”的钌螯合物Ru(dpphen)32+与脂肪酸类成膜分子以1:2混合时能够得到稳定的混合单分子膜.以十八烷基三氯硅烷（octadecayl trichloro silane, OTS）分子部分取代Ru(dpphen)32+,得到功能分子组份可控的混合单分子膜.研究表明,OTS分子在纯水表面上可以形成交联网状单分子膜结构,混入硬脂酸（SA）分子后,网状结构逐渐被破坏.SA含量增加,破坏的程度就增大,直至SA/OTS为3:1时,完全没有网状交联结构,形成可以用来沉积LB膜的均匀致密的单分子膜.表面离子Ru(dpphen)32+与OTS和SA一起构成三组份混合单分子膜,OTS和Ru(dpphen)32+为表面离子.单分子膜中混有Ru(dpphen)32+分子,可以有效地阻止OTS的交联发生,同时Ru(dpphen)32+/SA基团与OTS/SA基团是均匀共混的.改变Ru(dpphen)32+/SA基团与OTS/SA基团的混合比,即可以做到Ru(dpphen)32+的组份精确可控,得到可用来沉积LB膜的均一、稳定的单分子膜.     

Structural and topographical characteristics of adsorbed WPI and monoglyceride mixed monolayers at the air-water interface

In this work we have analyzed the structural and topographical characteristics of mixed monolayers formed by an adsorbed whey protein isolate (WPI) and a spread monoglyceride monolayer (monopalmitin or monoolein) on the previously adsorbed protein film. Measurements of the surface pressure (pi)-area (A) isotherm were obtained at 20 degrees C and at pH 7 for protein-adsorbed films from water in a Wilhelmy-type film balance. Since the surface concentration (1/A) is actually unknown for the adsorbed monolayer, the values were derived by assuming that the A values for adsorbed and spread monolayers were equal at the collapse point of the mixed film. The pi-A isotherm deduced for adsorbed WPI monolayer in this work is practically the same as that obtained directly by spreading. For WPI-monoglyceride mixed films, the pi-A isotherms for adsorbed and spread monolayers at pi higher than the equilibrium surface pressure of WPI are practically coincident, a phenomenon which may be attributed to the protein displacement by the monoglyceride from the interface. At lower surface pressures, WPI and monoglyceride coexist at the interface and the adsorbed and spread pi-A isotherms (i.e., the monolayer structure of the mixed films) are different. Monopalmitin has a higher capacity than monoolein for the displacement of protein from the air-water interface. However, some degree of interactions exists between proteins and monoglycerides and these interactions are higher for adsorbed than for spread films. The topography of the monolayer corroborates these conclusions.     

Study of molecular interaction in the mixed film of arachidic acid and metal beta-diketonate complexes by the "surface ions" method

Molecular interaction is very important for the mechanical properties and application of Langmuir films. In general, fatty acid film is stabilized by certain "subphase ions." In this work, two metal beta-diketonate complexes (M(tmhd)n, tmhd=2,2,6,6-tetramethyl-3,5-heptanedionate) were used as "surface ions" to form stable condensed films with different ratios at the air/water interface. The pi-A isotherms of the mixed films had been measured. The smaller molecular area of the metal beta-diketonate complexes indicated that the metal beta-diketonate complexes form multilayer condensed structures at high pressure at the air/water interface. However, arachidic acid (AA) retained a monolayer structure at high pressure in the mixed system. No considerable phase separations appeared during the compression of the mixed films, which indicated that the mixed films of metal beta-diketonate complexes and AA were miscible and stable. The molecular interaction of the two components in the mixed films was investigated in detail. Mixed systems with the mixing ratio of M(tmhd)n:AA=1:2 were chosen to study the effects of the interaction on the mechanical properties of the mixed films. The molecular interaction between AA and Ce(tmhd)4 is proved to be more significant than that between AA and Sr(tmhd)2, and the pi-A isotherms of the mixed films differ a lot from that of pure AA monolayer. Due to the strong intermolecular interaction, the liquid region disappears in the Ce(tmhd)4/AA mixed films, and dynamic elasticity is improved especially at high surface pressure. On the other hand, the interaction between the AA and the Sr(tmhd)2 is much weaker and the effects of the interaction on the properties (pi-A isotherm and dynamic elasticity) of the mixed films are not so significant, especially at low surface pressure. These results are in accordant with that of the UV spectra analyses.     

Effects of a central metal on the organization of 5,10,15,20-tetra-(p-chlorophenyl)-rare earth porphyrin hydroxyl compound at the air/water interface and in Langmuir-Blodgett films

Langmuir monolayers and Langmuir-Blodgett (LB) films of 5,10,15,20-tetra-(p-chlorophenyl) terbium/gadolinium porphyrin hydroxyl compound (TbOH and GdOH) and their mixtures with stearic acid (SA) in a molar ratio of 1:1 were investigated by Brewster angle microscopy (BAM), ultraviolet-visible (UV-vis), and infrared (IR) spectroscopy and atomic force microscopy (AFM). pi-A isotherms showed that well-defined Langmuir monolayers were formed at an air/water interface for the porphyrins and their mixture with SA. The BAM observations suggest that the pi-pi interaction between the GdOH molecules is stronger than that between the TbOH molecules. This result can be further confirmed by the AFM measurements. After the introduction of SA, the pi-pi interaction between the TbOH molecules is broken and thus two phases formed in the mixed LB film. However, it cannot break the stronger pi-pi interaction between the GdOH molecules. Therefore, no phase separation is observed in the GdOH/SA LB film. IR reflection-absorption (RA) spectra showed that the COOH groups of SA are partly converted to COO(-) groups, suggesting that there is an interaction between MOH and SA in the films. This interaction leads the benzene rings of TbOH to rotate toward parallel to the substrate and those of GdOH to rotate toward perpendicular to the substrate. All these results have demonstrated that the central metal ions have great effects on the organization and formation of the films.     

Monolayer characteristics of mixed octadecylamine and stearic acid at the air/water interface

Mixed monolayers of stearic acid (SA) and octadecylamine (ODA) at the air/water interface were investigated in this article. The miscibility of the two compounds was evaluated by the measurement of surface pressure-area per molecule (pi-A) isothems and the direct observation of Brewster angle microscopy (BAM) on the water surface. The two compounds were spread individually on the subphase (method 1) or premixed first in the spreading solvent and then cospread (method 2). The effect of spreading method on the miscibility of the two compounds was also studied. The results show that the mixed monolayers prepared by method 1 cannot get a well-mixed state. The isotherms of mixed monolayers preserve both characteristics of SA and ODA and exhibit two collapse points. The calculated excess surface area is very small. Besides, distinguished domains corresponding to those of pure SA and ODA can be inspected from the BAM images. Such results indicate that SA and ODA cannot get a well-mixed phase via 2-dimensional mixing. On the contrary, in the mixed monolayer prepared by cospreading, the two compounds exhibit high miscibility. In the pi-A isotherms, the individual characteristics of SA and ODA disappear. The calculated excess area exhibits a highly positive deviation which indicates the existence of special interaction between the two compounds. The low compressibility of isotherm implies the highly rigid characteristic of the mixed monolayer. which was also sustained by the striplike collapse morphology observed from the BAM. The rigid characteristic of SA/ODA mixed monolayer was attributed to the formation of "catanionic surfactant" by electrostatic adsorption of headgroups of SA and ODA or to the formation of salt by acid-base reaction.     

Study of molecular aggregation of artificial amyloid in a langmuir monolayer by infrared spectroscopy

A synthesized peptidolipid (C18IIGLM-NH2) comprised of a single C18-saturated hydrocarbon chain connected to the amino acid sequence IIGLM terminated with the NH2 group was spread on water, which formed a stable Langmuir monolayer. The Langmuir and Langmuir-Blodgett (LB) films have been characterized by measurements of surface pressure-area (pi-A) and surface potential-area (DeltaV-A) isotherms and infrared multiple-angle incidence resolution spectrometry (MAIRS). The Langmuir monolayer had a significantly larger limiting molecular area than that of a similar molecule of C18IIGLM-OH, which was reported in our previous study. The surface dipole moment analysis coupled with the pi-A isotherm suggested that the C18IIGLM-NH2 monolayer was extraordinarily stiff and the fundamental structure of the monolayer was brought about before the monolayer compression. The infrared MAIRS analysis of the C18IIGLM-NH2 LB film revealed that the backbone structure of the monolayer was the 'antiparallel' beta sheet aligned parallel to the substrate. Since the C18IIGLM-OH LB film was made of 'parallel' beta sheet with a random orientation, it has been found that the present C18IIGLM-NH2 Langmuir monolayer has a largely different monolayer structure, although the chemical structures are slightly different from each other by the terminal group only.     

The incorporation of C_(60) in cavities of 5,10,15,20-tetra-4-oxy(2-stearic acid)phenyl porphyrin in LB film

The structure and properties of mixed monolayer or LB film of 5,10,15,20-tetra-4-oxy(2-stearic acid)phenyl porphyrin/C60 were studied. A isotherms and small angle X-ray diffraction (SAXD) results show that C60 molecules were incorporated into the cavities of por-phyrin molecules in mixed monolayer and LB film . UV-vis spectra of mixed LB films show that the absorption intensity of porphyrin varied compared with pure porphyrin film, probably arising from the interactions between C60 and porphyrin ring. C60 molecules in mixed systems are well-dispersed. The TPP(CO2H)/C60 mixed LB film is a kind of two-dimensional host-guest system.     

Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers

In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)(2)(tmphen)]PF(6), (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air-water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as pi-A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at pi approximately equal to 37 mNm(-1). Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir-Blodgett) technique.