The Monolayer Behavior of Amphiphilic Polymer and Heterostructure of Polymer LB Film/CdS Clusters

In this paper we report the behavior of an amphiphilic polymer monolayer on pure water and Cd2+ subphase. This polymer was composed of hydrophilic ethylene diamine epichlorohydrin slightly crosslinked microgel and hydrophobic stearic chains, noted as ES-1. The introduction of Cd2+ ions in subphase had a marked effect on the process of the organization of the amphiphilic polymer at the air/water interface due to the association of Cd2+ ions with the hydrophilic network, which could be indicated by the pressure-area isotherms and Brewster Angle Microscopy. Ordered ES-1/Cd2+ LB multilayers were fabricated. After the multilayers reacted with H2S gas, CdS clusters were synthesized within the film, which was characterized by X-ray diffraction and UV-visible spectroscopy. Copyright 1999 Academic Press.     

Maximum withdrawal speed for Langmuir-Blodgett film deposition of arachidic acid

The maximum withdrawal speed of Langmuir-Blodgett (LB) film deposition of arachidic acid (AA) was investigated. The quality of LB deposited film was determined by the transfer ratio (TR), together with measurements of surface roughness using atomic force microscopy (AFM). A Langmuir mini-trough was used to provide the surface pressure versus molecular area (pi-A) curves and a flow visualization technique was applied to estimate the dynamic contact angles and to observe the fluid motion. The effects of hydrophobic and hydrophilic substrates, pH and the addition of four different ions, i.e., K+, Ba2+, Cd2+, and Al3+, on the withdrawal speed were examined. The "transition point" from liquid to solid states on the pi-A curve provided a clear indication of the maximum withdrawal speed. The lower the transition point, the higher was the maximum withdrawal speed. Stable deposition was possible only if the pH of the solution was maintained in a narrow range. The observation of dynamic contact angles and fluid motion, particularly the movement of air-liquid interface, was consistent with previous findings. Owing to the "soap effect" of the divalent ions Ba2+ and Cd2+, the maximum speed for successful LB film deposition without significant water entrainment could be extended substantially with the addition of divalent ions.     

Spectroscopic and optical characterization of porphyrin chromophores incorporated into ultrathin polyimide films

Polyamic acid (PAA) containing free-base porphyrin and zinc(II) porphyrin chromophores was synthesized by copolymerization of diphenylether-type tetracarboxylic dianhydride and diamines. The monolayer of the alkylamine salts of PAA (PAASs) at the air/water interface was deposited on solid substrates by the Langmuir-Blodgett (LB) technique. The PAAS LB films thus obtained were converted to polyimide (PI) LB films by chemical treatment. The fluorescence of porphyrin moieties in the PI LB film was observed, because of the weak electron-accepting properties of the diphenylether unit. Therefore, the photophysically important processes, such as photoinduced electron transfer, excitation energy transfer, and excitation energy migration could be investigated in relation to the layered nanostructures of the ultrathin PI films. The fluorescence spectrum suggested that the aggregation of porphyrin moieties in the PI LB films was effectively prevented by the use of polymeric films. The surface plasmon (SP) measurement showed that the thickness of the monolayers was 0.9-1.0 nm for PAAS films and 0.32-0.40 nm on average for PI LB films. The absorption dichroism of the Soret band of porphyrin indicated that porphyrin moieties in the PAAS and PI LB films are oriented in parallel with the substrate. These results showed that the orientation and the spatial distribution of porphyrin units can be efficiently regulated in the PI LB films in a nanometer dimension.     

Langmuir-Blodgett films composed of amphiphilic double-decker shaped polyhedral oligomeric silsesquioxanes

New amphiphilic polyhedral oligomeric silsesquioxanes (POSSs) were synthesized, and their monolayer behavior on a water surface and Langmuir-Blodgett (LB) film formation were studied. Two kinds of amphiphilic POSS molecules, which have two or four di(ethylene glycol) units (2OH-DDSQ and 4OH-DDSQ, respectively), were synthesized by direct hydrosilylation of di(ethylene glycol) vinyl ether with double-decker shaped polyhedral oligomeric silsesquioxanes (DDSQs). Surface pressure (π)-area (A) isotherms and Brewster angle microscope (BAM) measurements indicated that both amphiphilic DDSQs form a stable monolayer at the air-water interface. In addition, 4OH-DDSQ can be deposited on a solid substrate by the LB technique. Atomic force microscope (AFM) images of a one-layer 4OH-DDSQ film showed a homogenous uniform surface on a hydrophilic silicon substrate, whereas nanometer scale dots were formed on a hydrophobic silicon substrate. Multilayer deposition on a hydrophobic substrate resulted in an increase of dot size with increasing deposition number of layers. Moreover, homogenous multilayer films with a few voids were obtained on a hydrophilic substrate. The results indicate that 4OH-DDSQ is a good candidate for preparing hybrid nanoassemblies.     

Anodic electrodeposition of NiTSPP from aqueous basic media

The oxidative electrodeposition of NiTSPP (tetrakis(4-sulfonatophenyl) Ni porphyrin) on ITO electrode from 0.1 M NaOH aqueous solution has been studied, and UV-visible and reflection FTIR spectroscopies have been used to analyze the composition of such film. By use of UV-vis spectroscopy, small absorbance of the film and an almost nulling effect on the Soret band of the porphyrin along the Ni(III)/Ni(II) redox process were observed. The reflection FTIR spectroscopy detected the presence of Ni-OH groups in the reduced film and as well the state of the porphyrin molecules as radical cation. Moreover, the porphyrin has been quantified by means of the area of the vibration bands assigned to the sulfonate groups by using as reference a Langmuir-Blodgett film containing a known surface concentration of NiTSPP. These results lead us propose the formation of a conductor salt by electrocrystallization, with stoichiometries TSPP/Ni(II)(OH)2 and TSPP/Ni(III)OOH, for its reduced and oxidized forms, respectively. In these two forms, the porphyrin rings will be present as radical cation, which may be stabilized through its dimerization or polymerization.     

Fabrication of densely packed titania nanosheet films on solid surface by use of Langmuir-Blodgett deposition method without amphiphilic additives

Densely packed exfoliated nanosheet films such as Ti0.91O2, Ti0.8M0.2O2 (M = Co, Ni), Ti0.6Fe0.4O2, and Ca2Nb3O10 on solid substrates were prepared by the LB transfer method without any amphiphilic additives at the air-water interface. Nanosheet crystallites covered nearly 95% on the solid surface with minimum overlapping of nanosheets. The LB transfer method of the Ti0.91O2 nanosheet monolayer film is applicable for not only hydrophilic substrates such as quartz, silicon, indium-tin oxide (ITO), and glass but also the hydrophobic Au surface. On the basis of these points, the LB transfer method has advantages compared to the alternating layer-by-layer method, which makes use of oppositely charged polyelectrolytes such as poly(ethylenimine) (PEI). Adsorption of hydrophobic Ti0.91O2 nanosheets at the air-water interface is responsible for this LB transfer deposition method. The addition of tetrabutylammonium bromide into the subphase assisted the adsorption, causing an increase in the adsorbed amount of Ti0.91O2 nanosheets at the air-water interface.     

嵌入花生酸镉单层中的卟啉-紫精分子聚集行为的研究

本文制备了卟啉-紫精与花生酸镉混合LB膜, 用紫外可见光谱研究了膜中卟啉基团的聚集及取向, X射线衍射说明混合LB膜具有层状有序的周期结构。扫描电镜结果表明: 通过调节膜的表面压可使聚集成"微畴"的卟啉-紫精均匀分布在花生酸镉单分子层中, 随膜表面压的增大, 小的"微畴"相互连接形成更大的"微畴"。电子衍射说明混合膜中两组份分相存在, 且都为六角对称的有序结构。     

Fingerprinting Petroporphyrin Structures with Vibrational Spectroscopy. 4. Resonance Raman Spectra of Nickel(II) Cycloalkanoporphyrins: Structural Effects Due To Exocyclic Ring Size

Nickel(II) complexes of cycloalkanoporphyrins (CAPs) bearing a saturated carbon ring of varying size between pyrrole C(beta) and methine bridge carbon atoms are widespread in crude oil and related organic rich sediments. We have synthesized a series of NiCAPs containing meso,beta-ethano (NiCAP5), meso,beta-propano (NiCAP6), and meso,beta-butano (NiCAP7) groups and applied UV-visible absorption and resonance Raman (RR) spectroscopies to investigate the effects of the exocyclic ring size on the porphyrin structure and to establish vibrational CAP marker frequencies for petroporphyrins in fossil fuels. The RR spectra of NiCAPs, excited at or near porphyrin Soret ( approximately 400 nm) and Q (510-580 nm) bands are informative and display a rich array of skeletal and alkyl substituent modes. High-frequency (1300-1700 cm(-)(1)) structure-sensitive RR bands shift down considerably (up to 24 cm(-)(1)) with increasing size of the exocyclic ring, implicating increased nonplanar distortions of the tetrapyrrole macrocycle. Unlike in other petroporphyrins studied thus far, etio- and tetrahydrobenzoporphyrins, out-of-plane distortions of the porphyrin imposed by the meso,beta-cycloalkano ring are also sufficient to destroy the center of symmetry of the porphyrin pi-system and produce significant enhancement of the IR-active E(u) skeletal modes in the Q-band-excited RR spectra. The UV-visible absorption spectra also vary with the size of the exocyclic ring; both the Soret and Q bands progressively red shift as the cycloalkano chain becomes longer, implying a destabilization of the two highest occupied pi orbitals in NiCAP6 and NiCAP7. In addition, the size of the exocyclic ring in NiCAPs can be readily determined from the frequency of the approximately 900 cm(-)(1) marker band and the characteristic patterns of skeletal and substituent bands in the 700-1200 and nu(4) ( approximately 1380 cm(-)(1)) regions.     

修饰LB膜法制备的PEDOT薄膜对HCl气体气敏性的影响

以二十烷酸(AA)LB膜为模板, 通过3,4-乙烯二氧噻吩(EDOT)单体在LB膜亲水基团间聚合, 采用垂直拉膜方式在叉指电极上制备了不同层数的AA/PEDOT膜, 并对HCl气体在AA/PEDOT复合LB膜中的作用进行研究, 结果表明, 膜厚、处理温度、拉膜膜压对AA/PEDOT复合LB膜的HCl气体敏感性能有不同程度的影响. 在较小气体体积分数范围(20～60 μL/L)内, AA/PEDOT多层有序膜对气体表现出非线性响应特性, 而在较高浓度范围内则表现出线性响应特性. AA/PEDOT复合LB膜对30 μL/L HCl气体的响应时间约为20 s, 远快于普通PEDOT旋涂膜(约为80 s), 同时在膜压达到45 mN/m时, AA/PEDOT膜的敏感性能反而下降. 敏感机理解释为电子在PEDOT共轭系统和氧化性气体间的转移.     

Dis-aggregation of an insoluble porphyrin in a calixarene matrix: characterization of aggregate modes by extended dipole model

In this paper, the different aggregation modes of a water-insoluble porphyrin (EHO) mixed with an amphiphilic calix[8]arene (C8A), at the air-water interface and in Langmuir-Blodgett (LB) film form, are analyzed as a function of the mixed composition. The strategy used to control the EHO aggregation has consisted of preparing mixed thin films containing EHO and C8A, in different ratios, at the air-water interface. Therefore, the increase of the C8A molar ratio in the mixed film diminishes the aggregation of the EHO molecules, although such an effect must be exclusively related to the dilution of the porphyrin. The reflection spectra of the mixed C8A-EHO films registered at the air-water interface, show a complex Soret band exhibiting splitting, hypochromicity and broadening features. Also, during the transfer process at high surface pressure, it has been shown that the EHO molecules are ejected from the C8A monolayer and only a fraction of porphyrin is transferred to the solid support, in spite of a complete transfer for the C8A matrix. The complex structure of the reflection spectra at the air-water interface, as well as the polarization dependence of the absorption spectra for the mixed LB films, indicate the existence of four different arrangements for the EHO hosted in the C8A matrix. The aggregate formation is governed by two factors: the attraction between the porphyrin rings which minimizes their separation, and the alkyl chain interactions, that is, hydrophobic effect and/or steric hindrance which determine and restrict the possible aggregation structures. By using the extended dipole model, the assignment of the spectral peaks observed to different EHO aggregates is shown.     

Characterization of N-cyclohexylmethacrylamide LB thin films for room temperature vapor sensor application

This study reports the synthesis, characterization and gas sensing applications of N-cyclohexylmethacrylamide (NCMA) monomer material using FT-IR, ¹H and ¹³C NMR, UV-visible spectroscopy, Quartz Crystal Microbalance (QCM) and Langmuir-Blodgett (LB) thin film deposition techniques. The thin film deposition conditions of NCMA monomer material, which are prepared by LB film technique, are characterized by UV-visible spectroscopy and QCM system. The sensing behaviors of the LB film with respect to volatile organic compounds (VOCs) at room temperature are investigated. Surface pressure change as a function of surface area of NCMA molecule at the water surface shows a well-organized and stable monolayer at 18 mN m^?1 surface pressure value for LB film deposition. Transfer ratio values are found to be ≥ 0.94 for quartz glass and ≥ 0.93 for quartz crystal substrate. The typical frequency shift per layer is obtained 20.10 Hz/layer and the deposited mass onto a quartz crystal is calculated as 824.62 ng/layer. The sensing responses of the LB films against chloroform, dichloromethane, acetone, toluene, benzene and ethanol are measured by QCM system. The sensitivities of the NCMA LB film sensor are determined between 0.085 and 0.029 Hz ppm^?1. Sensitivities with detection limits are between 35.29 and 100.33 ppm against organic vapors. These results can be concluded that the monomer LB film sample is found to be significantly more sensitive to chloroform and dichloromethane vapors than others organic vapors used in this work. This material may find potential applications in the development of room temperature organic vapor sensing.     

Perfluorophenyl-Directed Giant Porphyrin J-Aggregates

Quadrupolar interactions of porphyrin bearing two pentafluorophenylethynyl terminals ( 1 ) drove the formation of a successive one-dimensional staircase structure, i.e., J-aggregates, to yield millimeter-length needles with a single-crystalline character in methylcyclohexane solution. In contrast, π-stacked interactions of porphyrin bearing two nonfluorinated phenyl terminals ( 2 ) formed no aggregates in solution. A spin-cast film of 1 also showed bathochromic shift of the Soret and Q bands, indicating the formation of J-aggregates. The molecular arrangement of the J-aggregates was revealed by microbeam glazing-incidence wide-angle X-ray diffraction (GIWAXD), and was in good agreement with the optimized structure generated by density functional theory (DFT) calculations.     

5,10,15,20-四-(4-N,N,N-二甲基十六烷基氨基苯基)卟啉LB膜结构的研究

研究了两亲性卟啉5,10,15,20-四-(4-N,N,N-二甲基十六烷基氨基苯基)卟啉(TDMC₁₆PP)在气/液界面上的成膜性能,制备了其多层LB膜。用UV-Vis吸收光谱、荧光光谱、偏振UV-Vis吸收光谱和小角X射线衍射对LB膜进行了测试表征。结果表明:两亲性卟啉TDMC₁₆PP具有良好的成膜性能,其LB膜性质稳定,有较好的结构均匀性和周期性。在LB膜内,脂肪链并不是直立的,卟啉大环平面与基片平面成42.5°排列。     

具有不同取代链长的卟啉衍生物LB膜的结构研究

本文研究了三种羧酸取代的四苯基卟啉衍生物在空气/Cd^2^+水溶液界面上所形成的单层膜及LB膜。这三种卟啉衍生物中, 一种没有脂链, 另外两种具有不同长度的脂链。由π-A等温线得到的平均表观分子面积相差很大。紫外-可见光谱表明, LB膜中卟啉的Soret吸收带相对于溶液的吸收均红移, 但红移程度不同。LB膜的偏振紫外-可见光谱表明, LB膜中三种卟啉衍生物的卟啉环具有基本一致的取向。运用亚相降低法得到了三种卟啉衍生物单层LB膜, 其紫外-可见光谱与用垂直提拉法得到的LB膜的紫外-可见光谱具有一致的特征。这些结果表明: 卟啉衍生物有无取代链及取代链长的不同对平均表观分子面积的大小和膜中环间的距离有影响, 但对环的取向没有影响。环的取向由环本身及环上的亲水取代基来确定。气/液界面上三种卟啉衍生物的单层膜中环也具有一致的取向, 且与LB膜中环的取向相差不大。提拉不会对膜中环的取向及膜的结构造成大的改变。     

Synthesis and Structure of PEDOT Prepared through a Modified LB Film Method

Adopting LB film method, an arachidic acid (AA)/PEDOT multilayer LB film and polymerized EDOT monomers in hydrophilic group of LB were chosen to prepare the arachidic acid (AA)/PEDOT multilayer LB film. UV-Vis, FT-IR and XPS analyses implied that EDOT was effectively polymerized in film, and thus PEDOT conducting polymer was produced. Analyses of XRR and SIMS indicated that the film had a well-arranged lamella structure, and further research showed that polymerization of EDOT in AA film destroyed the orderliness of the original LB film. This phenomenon could be related to the destructive effect of polymerization on the layered structure. We used four-point probe and semiconductor instrument to study the conductivity property of the film, and observed that the conductivity of AA/PEDOT film had sudden changes with the changes of processing time in an effective conduction network, which was caused by "permeability" in conducting channel of multilayer film. The test results also indicated that the conductivity of AA/PEDOT film was obviously better than that of spin-coating PEDOT/PSS or ODA-SA/PEDOT-PSS film due to the higher π structure of PEDOT structure and ordered film structure.     

Alkylamine sensing using langmuir-blodgett films of n-alkyl-N-phenylamide-substituted zinc porphyrins

Two porphyrin compounds, zinc(II) 5,10,15,20-tetrakis(3,5,5-trimethyl- N-phenylhexanamide)porphyrin and zinc(II) 5,10,15,20-tetrakis(2,2-dimethyl- N-phenylpropanamide)porphyrin, have been investigated as possible candidates for the detection of alkylamines. UV-visible spectroscopy has shown that their solution absorption spectra are significantly modified upon interaction with a range of organic analytes, including acetic acid, butanone, ethylacetate, hexanethiol, octanal, octanol, alkylamines, and trimethylphosphite. Large spectral changes are observed for the family of alkylamines as a result of the specific affinity between zinc and the amine moiety. Langmuir-Blodgett (LB) films of the porphyrins have been fabricated in order to assess their solid-state sensing capability toward amines. The surface pressure-area (Pi- A) isotherms reveal a clear three-phase Langmuir film behavior and show that these monolayer films may be compressed to a relatively high surface pressure ( approximately 40-50 mN m (-1)). The isotherm data alongside molecular modeling suggest a relatively flat orientation of the porphyrin rings of both compounds: that is, a mutually parallel alignment of the plane of the porphyrin ring and that of the water surface. LB films deposited at 15 mN m (-1) have been exposed to alkylamine vapor (carried by N 2). A red shift and increase in intensity of the Soret band absorbance is observed which can be reversed by flowing pure N 2 over the gently heated sample (60 degrees C) after exposure. Primary amines were expected to invoke the greatest sensing response due to (i) their larger association constants with these porphyrins compared to secondary and tertiary amines and (ii) the ease of diffusion of amines which is expected to follow the order primary > secondary > tertiary due to the steric hindrance arising from the bulky secondary and tertiary amines. However, the magnitude of the absorbance change is largest for exposure to the secondary amines, dipropylamine and dibutylamine, for both porphyrins, compared to primary and tertiary amines. This trend follows that observed when the amines were added to solutions of the porphyrins. The rate of response of the porphyrin LB films falls as the molecular weight of the diffusing alkylamine increases. Furthermore, a greater rate of response is observed for the phenylhexanamide porphyrin compared to the phenylpropanamide porphyrin due to its lower molecular density within the LB film and therefore more porous structure.     

Photoinduced electron transfer in Langmuir-Blodgett monolayers of porphyrin-fullerene dyads

A series of electron donor-acceptor (DA) dyads, composed of a porphyrin donor and a fullerene acceptor covalently linked with two molecular chains, were used to fabricate solid molecular films with the Langmuir-Blodgett (LB) technique. By means of the LB technique, the DA molecules can be oriented perpendicular to the plane of the substrate. In DHD6ee and its zinc derivative hydrophilic groups are attached to the phenyl moieties in the porphyrin end of the molecule; while in the other three dyads, TBD6a, TBD6hp, and TBD4hp, the hydrophilic groups are in the fullerene end of the molecule. This makes it possible to alternate the orientation of the molecules in two opposite directions with respect to the air-water interface and to fabricate molecular assemblies in which the direction of the primary photoinduced vectorial electron transfer can be controlled both by the deposition direction of the LB monolayer and by the selection of the used DA molecule. This was proved by the time-resolved Maxwell displacement charge measurements. The spectroscopic properties of the DA films were studied with the steady-state absorption and fluorescence methods. In addition, the time correlated single photon counting technique was used to determine the fluorescence properties of the dyad films.     

单、 双及双混氮杂卟啉的结构和电子吸收光谱

利用密度泛函和含时密度泛函理论对卟啉(FBP)、 单氮杂卟啉(N/Neo-CPs)、 双氮杂卟啉(DNCPs)及双混氮杂卟啉(Neo-C-NCPs)的结构与电子吸收光谱进行了研究. 结果表明, 由于N/C位置改变, 分子对称性和轨道组成发生改变, 氮杂卟啉中2-NCP-2H, 2,18-DNCP-2H 和1,17-Neo-C-NCP的各前线和近前线轨道能级发生较大变化, 光谱峰红移较显著; 电子-空穴分布图表明3类氮杂卟啉电子跃迁途径更丰富. 进一步探讨了水、 氯仿和苯3种溶剂对4类卟啉分子的影响. 结果表明, 随着溶剂极性减小, FBP, N-/Neo-CPs, DNCPs和Neo-C-NCPs的Q带吸收峰红移越明显, 吸收略有增强.     

Molecular Engineering of Push–Pull Porphyrin Dyes for Highly Efficient Dye‐Sensitized Solar Cells: The Role of Benzene Spacers

Porphyrins have drawn much attention as sensitizers owing to the large absorption coefficients of their Soret and Q bands in the visible region. In a donor and acceptor zinc porphyrin we applied a new strategy of introducing 2,1,3‐benzothiadiazole (BTD) as a π‐conjugated linker between the anchoring group and the porphyrin chromophore to broaden the absorption spectra to fill the valley between the Soret and Q bands. With this novel approach, we observed 12.75 % power‐conversion efficiency under simulated one‐sun illumination (AM1.5G, 100 mW cm^?2). In this study, we showed the importance of introducing the phenyl group as a spacer between the BTD and the zinc porphyrin in achieving high power‐conversion efficiencies. Time‐resolved fluorescence, transient‐photocurrent‐decay, and transient‐photovoltage‐decay measurements were employed to determine the electron‐injection dynamics and the lifetime of the photogenerated charge carriers.     

Excited states of porphyrin macrocycles

S1 --> S(n) spectra of porphyrin, diprotonated porphyrin, and tetraoxaporphyrin dication have been measured in the energy range 2-3 eV above S1 at room temperature in solution by means of transient absorption spectroscopy exciting with femtosecond pulses. Highly excited pi pi* states not active in the conventional S0 --> S(n) spectrum have been observed. The experimental data are discussed on the basis of the time dependent density functional theory taking advantage of large scale calculations of configuration interaction between singly excited configurations (DF/SCI). The DF/SCI calculation on porphyrin has allowed to assign g states active in the S1 --> S(n) spectrum. Applying the same calculation method to tetraoxaporphyrin dication the S0 --> S(n) spectrum is reproduced relatively to the Q and B (Soret) bands as well as to the weaker E(u) bands at higher energy. According to our calculation the S1 --> S(n) transient spectrum is related to states of g symmetry mainly arising from excitations between doubly degenerate pi and pi* orbitals such as 2e(g) --> 4e(g). In the case of diprotonated porphyrin it is shown that the complex of the macrocycle with two trifluoroacetate anions plays a significant role for absorption. Charge transfer excitations from the anions to the macrocycle contribute to absorption above the Soret band, justifying the intensity enhancement of the S0 --> S(n) spectrum with respect to the other two macrocyclic systems.