共查询到20条相似文献,搜索用时 15 毫秒
1.
Hirano Y Tateno S Yamashita Y Ozaki Y 《The journal of physical chemistry. B》2008,112(45):14158-14167
We have investigated the thermal behavior of H-aggregate in a mixed Langmuir-Blodgett (LB) film of the merocyanine dye (MS18)-arachidic acid (C20)- n-octadecane (AL18) ternary system by means of UV-visible and IR absorption spectroscopy in the range from 25 to 250 degrees C with a continuous scan. The results of both UV-visible and IR spectra indicate that the temperature-dependent variation in MS 18 aggregation state is linked not only with the degree of intramolecular charge transfer and the behavior of packing, orientation, conformation, and thermal mobility of the MS18 hydrocarbon chain but also with the presence and absence of AL18. The H-aggregate dissociates from 25 up to 50 degrees C, which is caused by the AL18 evaporation from the mixed LB film and the increment of thermal mobility of the MS18 hydrocarbon chain. From 110 to 160 degrees C, blue-shifted bands, attributed to the oligomeric MS18 aggregation, appear near 515 nm in the MS18-C 20-AL18 ternary system as well. The temperature at which the 515 nm band occurs is identical for both present ternary system and previously investigated MS18-deuterated arachidic acid (C20- d) binary system, and it is in good agreement with the melting point (110 degrees C) of cadmium arachidate (CdC20). Therefore, it is indicated that the driving force which induces the 515 nm band comes from the melting phenomenon of CdC20 molecules which are phase-separated from MS 18 molecules in as-deposited LB films. 相似文献
2.
Hirano Y Tateno S Ozaki Y 《Langmuir : the ACS journal of surfaces and colloids》2007,23(13):7003-7013
We have investigated the thermal behavior of J-aggregates in the mixed Langmuir-Blodgett (LB) films composed of the merocyanine dye (MS18)-deuterated arachidic acid (C20-d) binary system in the temperature range from 25 to 250 degrees C by means of UV-visible and IR transmission absorption spectroscopy. The temperature-dependent variations in both UV-visible and IR absorption spectra indicate that the MS18 aggregation states are linked with the MS18 intramolecular charge transfer and the behavior of the packing, orientation, conformation, and thermal mobility of the MS18 hydrocarbon chain. The J-aggregate formed at 25 degrees C in the mixed LB films dissociates in the temperature range from 25 to 110 degrees C, which is mainly ascribed to the increase in the thermal mobility of MS18 hydrocarbon chain and the dissociation of the chelation by a cadmium ion to the MS18 keto group. A thermally induced blue-shifted band appears at around 515 nm from 110 to 160 degrees C. This band is attributed to oligomeric aggregation with side-by-side alignment of the MS18 transition dipole moments on the basis of the shift to a higher-energy side, broadening, and temporary increment of the MS18 intramolecular charge transfer of the band. Consequently, the appearance of the thermally induced blue-shifted band indicates the possibility that the MS18 aggregation states can be controlled from the red shift to the blue shift by the annealing method adopted in the present study. 相似文献
3.
Takahashi M Okuhara T Yokohari T Kobayashi K 《Journal of colloid and interface science》2006,296(1):212-219
Photoactive film material of long-chain azobenzene derivative, p-(omega-trimethylammoniodecyloxy)-p'-octyloxyazobenzene bromide (TAOAB), was fabricated into a Langmuir-Blodgett (LB) film by a polyion-complex technique using poly(sodium 4-styrenesulfonate) as a polyanion. To investigate the effect of the packing state of the azobenzene chromophore on its orientation and cis-trans isomerization, TAOAB was mixed with methyl stearate in the LB film matrix at various mole fractions (X(TAOAB)), and structural characterizations were subsequently carried out by means of Fourier transform infrared and ultraviolet-visible spectroscopies, X-ray diffraction analysis, and atomic force microscopy. The results obtained show that as the degree of packing increases, both the azobenzene chromophores and the hydrocarbon chains orient more perpendicularly to the surface of the LB film. In addition, reversible cis-trans photoisomerization of TAOAB took place upon alternate irradiation with UV and visible light even in a mixed LB film with the chromophores in a dense lateral packing state. In the process of thermal cis-to-trans isomerization, we found that the reaction rate is strongly affected by the packing state of TAOAB at 20 degrees C, reflecting the differences in steric hindrance among LB films of various X(TAOAB). In addition, higher activation energy was obtained for thermal cis-to-trans isomerization when the free volume around the chromophores became smaller. 相似文献
4.
《Vibrational Spectroscopy》2007,43(1):86-96
The structure of a merocyanine dye (MS) in red- and blue-shifted aggregates involving J- and H-aggregates in mixed LB films of MS–arachidic acid (C20) binary and MS–C20-n-octadecane (AL18) ternary systems ([MS]:[C20]:[AL18] = 1:2:x; x = 0, 1.0, 2.0, 3.0, 4.0 and 5.0) fabricated using an aqueous subphase containing Cd2+ ions has been investigated by means of polarized visible and infrared spectroscopy. Not only the AL18 molecules mixed as a third component but also the Cd2+ ions added to distilled water for the subphase used turn out to be the significant elements for the formation of the MS aggregates in all the ternary systems. It has been found that the degree of the MS intramolecular charge transfer strongly depends on the aggregation states; the J-aggregate (x = 0), H-aggregate (x = 1.0), oligomer (x = 2.0) and relatively small aggregates (x = 3.0, 4.0 and 5.0), and that the stabilization by the intramolecular charge transfer for the formation of the MS aggregates is induced according to the individual aggregation states. The gauche conformation is clarified to be slightly involved in the MS hydrocarbon chains for all the binary and ternary systems. The long axis of the MS hydrocarbon chains in the J-aggregates, being fairly tilted from the film normal, gradually approaches to the film normal with the increasing AL18 content up to x = 2.0 with the orientation of the long axis of the MS hydrocarbon chains remaining constant in the subsequent ternary systems. It can be concluded that the formation of the red- and blue-shifted aggregates is ascribed to the difference in the MS slippage which can also be regulated by the degree of the orientation of the MS hydrocarbon chains, and that the decrease in the size of the MS aggregates accompanied by the increasing AL18 content is due to the blocking by the AL18 molecules being out of the empty space on the MS chromophore. 相似文献
5.
Miguel Gd Pérez-Morales M Martín-Romero MT Muñoz E Richardson TH Camacho L 《Langmuir : the ACS journal of surfaces and colloids》2007,23(7):3794-3801
The molecular organization of a mixed film, containing a water-soluble tetracationic porphyrin (TMPyP) and a p-tert-butyl calix[8]arene octacarboxylic acid derivative (C8A), at the air-water interface and on a solid support (LB film), has been investigated. Although the TMPyP aggregation was not detected at the air-water interface, TMPyP J-aggregates have been found in the LB films (Y-type). Unlike tetraanionic porphyrins, for example TSPP, the TMPyP J-aggregates are not induced by a zwitterion formation. The TMPyP J-aggregation is a result of a "double comb" configuration, where porphyrins from opposite layers are interwoven in a linear infinite J-aggregate. Our results confirm that TMPyP molecules tend to self-aggregate strongly, provided the electrostatic repulsions of their peripheral groups are cancelled by the anionic groups of the C8A matrix. 相似文献
6.
Structural changes of the Langmuir-Blodgett (LB) films of azobenzene accompanied by photoisomerization are described. First, photoisomerization is explained in terms of 'free volume'. In the polyion complex monolayers of amphiphiles having two azobenzene units at the air-water interface, the area per molecule depends on the polycation species. The fraction of cis-azobenzene in the LB films at the photostationary state under the illumination with UV light increased with increasing area per molecule, which is consistent with the concept of free volume. Second, a counter example of the concept of free volume is presented. Three-dimensional cone-shaped structures developed with trans-to-cis photoisomerization in the polyion complex LB film of a water-soluble amphiphilic azobenzene. These structures appeared and disappeared reversibly by alternate illumination with UV and visible light. The results indicate that the two-dimensional LB film structure exerts significant modification by photoisomerization. This is against the concept of free volume because this concept does not consider the possibility that the two-dimensional LB film structures may change into three-dimensional ones. Finally, photo-induced J-aggregate formation of non-photochromic and photochromic dyes is described. Two cyanine dyes were each mixed with an amphiphilic azobenzene in the LB films. These cyanine dyes are known to form J-aggregates in single-component LB films. In the mixed LB films, the J-aggregate formation was suppressed to some extent. The alternate illumination of the films with UV and visible light caused the photoisomerization of azobenzene in the mixed LB films, which triggered the J-aggregate formation of the cyanine dyes. The J-aggregate formation was accompanied by the development of three-dimensional cone-shaped structures from the film surface. When an amphiphilic merocyanine was mixed with the azobenzene in the LB films, J-aggregate formation was also induced by the alternate illumination with UV and visible light. This J-aggregate formation was also accompanied by a large morphological change: circular domains changed into fractal-like ones. The J-aggregate formation of the dyes and the concomitant morphological change were irreversible. In these cases, the photoisomerization of azobenzene served as a trigger to induce self-organization of the dye molecules. 相似文献
7.
A series of gemini amphiphiles with a pyridinium headgroup and rigid spacers were designed, and their interfacial assemblies with cyanine dyes, 3,3-disulfopropyl-9-methyl-selenacarbocyanine (SeCy) and 3,3-disulfopropyl-4,5,4',5'-dibenzo-9-methyl-thiocarbocyanine (MTC), through the air/water interface were investigated. Although the dyes have intrinsic tendencies to form J- or H-aggregates in aqueous solutions, their aggregation could be regulated in the complex films. Depending on the spacer, both J- and H-aggregates were formed for SeCy, whereas an H-aggregate with different absorption bands was obtained for MTC. Furthermore, the formed aggregates in the films could be reversibly switched by treating the complex films with HCl, NH3 gas, or water vapor. The J-aggregates of SeCy could be changed into H-aggregates and recovered through an alternative HCl/NH3 exposure in the films. The H-aggregate of the MTC film could be changed into J-aggregate upon exposure to HCl gas and subsequently put into air or NH 3 gas, and the thus-formed J-aggregate could be changed into H-aggregate under hot water vapor. In addition, such a reversible switch between different aggregates of MTC was only observed when the gemini amphiphiles with rigid spacers were applied. A possible explanation related to the protonation of the dye and the reorganizations in the film during the interconversion between different aggregates was proposed. 相似文献
8.
9.
The tunable self-assembly of a fullerene (C(60))-N,N-dimethylaminoazobenzene (DPNME) molecular system as a function of solvent polarity in THF/water binary solvent is reported. Gradual increase of the volume fraction of the nonsolvent water in a 1×10(-5) M THF solution of DPNME at a mixed dielectric constant ε(mix)≈42 resulted in initial redshifting of the (1)(π→π(*)) absorption band, which signified the 1D head-to-tail or J-type arrangement of the DPNME molecular system. Further increase in the solvent polarity to ε(mix)≈66 evidenced formation of an antiparallel head-to-tail or H-type molecular arrangement in conjunction with the J-aggregates, thereby establishing a solvent-polarity-dependent dynamic equilibrium between the monomer ? J-aggregate ? H-aggregate. The controlled aggregation was governed by the synergetic effect of intermolecular donor-acceptor interaction between the electron-deficient fullerene ring and the electron-rich N,N-dimethylamino-substituted aromatic ring; typically, van der Waals and π-π interactions between the molecules constituting a pair of dimers were envisaged. An agreement between the semiempirically calculated drastically reduced oscillator strength of the DPNME H-dimer in the antiparallel configuration (0.69 vs. 1.29 in the monomeric DPNME) and the experimental electronic absorption spectra beyond ε(mix)=66 further strengthened this assignment to the hitherto forbidden antiparallel H-dimer. Complementing the above, the periodicity of molecular self-assembly dictated a monoclinic unit cell in the single-crystal XRD packing pattern with a C2/c space group; the molecules packed laterally with mutual interdigitation with the donor (E)-N,N-dimethyl-4-(p-tolyldiazenyl)aniline (AZNME) parts in an antiparallel fashion (contrary to the usual expectation for H-aggregates) with strong inter- and intrapair van der Waals and π-π interactions between the constituent fullerene moieties. Unlike those of porphyrin/phthalocyanine bowl-like donor-initiated architectures, a rare class of DPNME dyadic supramolecular self-assemblies was realized with π-extended 2D fullerene networks, in which the linear geometry of the AZNME donor and the conformational rigidity of the fullerene acceptor played crucial roles. 相似文献
10.
Y6 (BTP-4F) is one of the novel non-fullerene acceptors and its photo-physics significantly affects the efficiency of organic solar cells. Here, the photo-induced energy and charge transfer (CT) dynamics in four typical dimers (Y, C, S1, and S2)-TYPE from Y6 films are revealed by combining electronic structure theory calculations, rate theories, and quantum dynamics simulations. The rate theories show that in ground-state CT processes the Y-TYPE is bipolar with the largest rate among all dimers, and in excitation energy transfer the triplet rates are about 105 smaller than the singlet ones, however, the singlet rates can reach 1013s−1, which may lead to the rate theories invalid. The stochastic Schrödinger equation based on the diabatic Hamiltonian is thus adopted to reveal excited-state dynamics. The results show that three of the four dimers are H-aggregate except for S1-TYPE with J-aggregate property. However, these J/H-aggregate properties are excited-state dependent, for instance, the Y-TYPE becomes J-aggregate in the second excited-state. Furthermore, CT states are strongly mixed with the first two excited states, which can dramatically impact the energy transfer. Indeed, the dynamic simulations clarify that the excited-state energy relaxation mediated by CT states can be performed in the first 20 fs, and the CT-state population is even non-negligible in the quasi-stationary distribution. 相似文献
11.
Egawa Y Hayashida R Anzai J 《Langmuir : the ACS journal of surfaces and colloids》2007,23(26):13146-13150
We fabricated a layer-by-layer (LbL) film composed of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and poly(allylamine) (PAA) and investigated its pH response by UV-visible spectrometry. When the (PAA/TPPS)5PAA film was immersed in a pH 1.5 solution, J-aggregate bands were observed at 484 and 691 nm. Above pH 3.0, the J-aggregates were completely dissociated and an H-aggregate band was observed at 405 nm. The interconversion between the J-aggregates and H-aggregates in the LbL film was repeatable and controllable by changing the pH of the solutions. 相似文献
12.
Matsumoto M Nakazawa T Mallia VA Tamaoki N Azumi R Sakai H Abe M 《Journal of the American Chemical Society》2004,126(4):1006-1007
We have found a thermal hysteresis in the photoresponsivity of a Langmuir film for the first time. The Langmuir film of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-8-(docosanoyloxymethyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP) was fabricated at 13 degrees C at 10 mN m-1, followed by heating to a given temperature. UV irradiation of this film caused only the isomerization of SP to the corresponding merocyanine (MC) up to 29 degrees C. Light-induced J-aggregation of MC occurred at 30 degrees C. On the other hand, once the film was heated to 30 degrees C, light-induced J-aggregation was observed down to 27 degrees C. The hysteresis should be related with the phase transitions that occur in the bulk of SP at similar temperatures. No significant morphological change occurred by light-induced J-aggregation in the Langmuir-Blodgett (LB) film of SP by the present method, in contrast to the case of the LB films fabricated under isothermal conditions at 30 degrees C. This feature enabled us to pattern the LB film with J-aggregate of MC by UV irradiation through a photomask of lines with a width of 5 mum each. 相似文献
13.
电荷转移配合物薄膜制备方法和结构表征的研究进展 总被引:1,自引:0,他引:1
回顾了与Langmuir-Blodgett(LB)技术有关的电荷转移配合物薄膜的各类制备方法、结构表征结果,并比较了制备方法对薄膜结构的影响.例如,将LB膜C18H37TCNQ(电子受体)插入到电子给体3,3’,5,5’-tetramethylbenzidine(四甲基联苯胺, TMB)的石油醚溶液中进行掺杂,制备了TMB•C18H37TCNQ电荷转移配合物薄膜.在这种薄膜中,给体和受体以面对面的方式堆积,两者的环平面与基片平面接近垂直.而采用硬脂酸和C18H37TCNQ的混合LB膜通过类似的掺杂路线制备的TMB•C18H37TCNQ薄膜的结构发生了一些变化,例如其长的烃链C18H37更加垂直于基片平面.通过比较以前的各种实验结果可以得出以下结论:电荷转移配合物的结构可以通过制备方法得到控制. 相似文献
14.
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. 相似文献
15.
Dos Santos DS Pavinatto FJ Balogh DT Misoguti L Oliveira ON Mendonça CR 《Journal of colloid and interface science》2004,276(1):138-142
In situ UV-vis absorbance measurements are used to investigate aggregation in Langmuir films from the azopolymer poly[4'-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13), a methacrylate derivative of DR13. The level of aggregation in a Langmuir film is intermediate between that of HPDR13 in chloroform solution and in a deposited LB film, as expected. Absorption is negligible at large areas per monomer, and starts to increase at a critical area that is the same as the one obtained in surface potential isotherms, being close to twice the area per monomer for a condensed film. This indicates that the onset for light absorption coincides with a critical packing density where monolayer structuring occurs and there is a sharp change in the effective dielectric constant of the film/water interface. Consistent with a featureless pressure-area isotherm for HPDR13, denoting no significant molecular rearrangement upon film compression, the UV-vis spectra did not vary with the surface pressure. The intensity of absorbed light increased, though, as the film was compressed owing to a higher density of chromophores. At higher subphase temperatures, larger flexibility of HPDR13 chains led to a more compact arrangement, causing the area per monomer to decrease and the absorbed light to increase-with approximately opposite trends. 相似文献
16.
LIU Hong-Guo FENG Xu-Sheng YANG Kong-ZhangInstitute of Colloid Interface Chemistry Shandong University Jinan Shandong ChinaCHENG Chuan-Fu LI Jian Department of Physics Shandong Normal University Jinan Shandong ChinaLIANG Wei-AnDepartment of Chemistry Shandong University Jinan Shandong China 《中国化学》1995,13(5):415-422
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. 相似文献
17.
Hasegawa T Sato Y Kakuda H Li C Orbulescu J Leblanc RM 《The journal of physical chemistry. B》2008,112(5):1391-1396
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. 相似文献
18.
YANG Wensheng JIANG Yueshun CHAI Xiangdong LI Tiejin FU Lianshe ZHANG Hongjie 《中国科学B辑(英文版)》2000,43(5):555-560
Aggregation behavior of two amphiphilic D-π-A molecules bearing barbituric acid as both recogniton group and electron-drawing substituent , 5-(4-dodecyl oxybenzylidene)-(1H, 3H)- 2,4,6-pyrimidine trione (PB12) and 5-(4-N,N-didodecyl aminobenzylidene)-(1H,3H)-2,4,6-pyrimidine trione (AB12) was studied by UV-visible, fluorescence, and surface voltaic spectroscopies (SPS). The experimental results indicate that PB12 tends to form J-aggregate and AB12 tends to form H-aggregate under increasing concentration. An intramolecular twisted charge transfer (TICT) emission around 500 nm is observed when J-aggregate is formed between PB12 molecules, and an excimer emission around 600 nm is observed when H-aggregate is formed between AB12 molecules. 相似文献
19.
Langmuir-Blodgett (LB) films of N-octadecanoyl-L-alanine and its silver and zinc complexes have been investigated by variable-temperature Fourier transform infrared transmission spectroscopy. The thermal stability of LB films is improved through an intermolecular hydrogen bond and metal complex. The intermolecular hydrogen-bonding interaction between hydrophilic head groups in the same monolayers and the metal complex between one head group and another in the neighboring monolayers considerably increase the interaction between the corresponding hydrophobic alkyl chains. It is shown that the transformation of the triclinic subcell packing of the molecules in the LB films prior to and after the silver complex into hexagonal packing occurs before the phase transition accompanied with a change in molecular orientation. The phase transition behavior of the LB films is varied from a small temperature interval to large one depending on the hydrogen bond and metal complex. 相似文献