九州大学学術情報リポジトリ
Kyushu University Institutional Repository
フタロシアニン超薄膜と超分子構造に関する研究
藤木, 道也
https://doi.org/10.11501/3065641
出版情報：Kyushu University, 1992, 博士（工学）, 論文博士 バージョン：
権利関係：
ULTRATHIN FILMS AND SUPRAMOLECULAR ARCIDTECTURE OF PHTHALOCYANINE DERIVATIVES
1993
MICHIYA FUJIKI
CHAPTER 1: OVERVIEWS
CONTENTS
§ 1-1. Material Designs of Functional Molecules and Thin Film Preparation
Techniques . . . l
§ 1-2. Historical View of Phthalocyanines and Langmuir-Blodgett Films . . . ... . . 5
§ 1-3. Purpose and Contents of the Present Thesis ... 10
§ 1-4. References . .. . . ... . . ..... . . ... . . .... . . ... . ... . . . ... . . . .... . . ... ... . . 12
CHAPTER 2: SELF-ASSEMBLING PHENOMENA OF NICKEL PHTHALOCY A NINES SUBSTITUTED WITH ALKYLAMIDES §2-1. Introduction ... 19
§2-2. Chemical Structure of Phthalocyanines with Alkylamide Substituents . . . 20
§2-3. Electronic Absorption Spectra of the Phthalocyanine Assemblies ... . . ... . . 20
§2-4. Calculation of Q-band Spectral Shift Using Molecular Exciton Theory . . . 24
§2-5. Evaluation of Q-band Spectral Shift Using a Modified Molecular Exciton Theory . . . ...... .... . ... . . ... . . ..... . . . ... . .. .. . .. ... . . . .... .. . .... . ... . ... . . ... . . . ... . . .. 26
§2-6. Further Evidence of One-Dimensional Self-Assembling Feature . . . ..... . 26
§2-7. Preparation of Phthalocyanines with Alkylamide Substituents ... . . ... 29
§2-8. Conclusion . . . .... . . ... . . ... . . ... . ... . . ... . . 31
§2-9. References ... 32
CHAPTER 3: IN-PLANE DICHROISMS OF PHTHALOCYANINE LANGMUIR-BLODGETT FILMS §3-1. Introduction ... 35
§3-2. Evaluation of the Phthalocyanine Assemblage in Langmuir- Blodgett Film ... 36
§3-3. Force-Area Isotherms of the Phthalocyanine Assemblies . . . ... . . ... . . ... 37
§3-4. Dichroism of the Phthalocyanine Langmuir-Blodgett Films by Polarized UV-Visible Absorption Spectroscopy . . . ... ... . . 39
§3-5. Dichroisms of the Phthalocyanine Langmuir-Blodgett Films by Polarized IR Absorption Spectroscopy ... 43
§3-6. Effect of Deposition Conditions on the Phthalocyanine Assemblies .... . . 45
§3-7. Orientation Mechanism of the Phthalocyanine Assemblies .. . ... . . ... ..... 45
§3-8. Preparation of Langmuir-Blodgett Films . . . ... . ... . . ... ... . . ... . . ... . .... . . 46
§3-9. Conclusion . . . ..... . . ... . . ... . . ... . . ... . ... . . ...... . . ... . . 47
§ 3-1 0. References ... 4 7
CHAPTER 4: DIRECT PATTERNING AND ELECTRICAL PROPERTIES OF ALKYLAMIDE SUBSTITUTED PHTHALOCY ANINE THIN FILMS
§4-1.
§4-2.
§4-3.
§4-4.
§4-5.
§4-6.
§4-7.
§4-8.
§4-9
Introduction .. ................ ...... .... ...................... 51
Electrical Conductivity ................... ....... ......... 52
Patterning Properties of Phthalocyanine Thin Films ....................... ... ....... 53
Cross-Linking Reaction Mechanism ............. . .............. .. ....... 55
Dry Etching Durability ....................... ................. . . ... 58
Fine Patterns Using Electron Beam Lithography ................ ........ 59
Preparation of the Phthalocyanine Thin Films ... . . ... ......... ... .. . .. . ....... 59
Conclusion ........... . ..... ...... . .. .. ..... .. ......... . . ......... 60
References .. ... ... ............... .. ................. . . . ... . .............. 60
CHAPTER 5: FACILE SYNTHESES OF SOLUBLE PHTHALO CY ANINES WITH SHORT ALKYL SUBSTITUENTS §5-1. §5-2. §5-3. §5-4. §5-5. §5-6. §5-7. §5-8. Introduction ... ... . ...... ... . . . ................ 63
Synthetic Schemes ............................................. 64
Bromination of Alkylbenzene Derivative ........... .......... 66
Characterization of Geometric Isomers of Tetra-Substituted Phthalocyanines ............... .. . . ... . ....... . .. .......... 68
Syntheses of Lead II Tetra(tert-butyl)phthalocyanine ............... 74
Preparation of Lightly Substituted Phthalocyanines and Their Intermediates ............ ..... . . ..... . ..................... . . .. ... 74
Conclusion ................................ ... ................... . . . ....... 77
References .............................. .............. 78
CHAPTER 6: CHARACTERIZATION OF LANGMUIR-BLODGETT FILMS OF PHTHALOCY ANINES WITH SHORT ALKYL SUBSTITUENTS §6-1. Introduction ........................ . ................. . ... 79
§6-2. Force-Area Isotherms .... . . ... . . .................................... . . .................... 80
§6-3. UV-Visible Absorption Spectra ......... . . ... ........... 80
§6-4. Powder X-Ray Diffraction Patterns .................. ......... 81
§6-5. Assembled Structures .................... . . . ................ 83
§6-6. Conclusion ................ .. . . . ................ 85
§6-7. References .................................... : ... 85
ii CHAPTER 7: ELECTRICAL PROPERTIES OF LANGMUIR BLODGETT FILMS OF PHTHALOCY A NINES WITH SHORT ALKYL SUBSTITUENTS §7-l. §7-2. §7-3. §7-4. §7-5. §7-6. §7-7. §7-8. Introduction ... 87
Experimental ..... . . . .................................................. 88
In-Plane Conductivity of Langmuir-Blodgett Films ... . . . ... . . . ........ 88
Response in Conductivity Change under Exposure to Active Gases ...... ... 89
Theories for Electrical Conductivity ...... .............................. . 92
Relation Between Electrical Responses and Electronic Potential Parameters ............................. ... ... 93
Conclusion .......... ......... .. . ...... ........ 95
References .......... . .................... 95
CHAPTER 8: NEW TETRAPYRROLIC MACROCYCLE: a,�,'Y-TRIAZATETRABENZCORROLE §8-1. §8-2. §8-3. §8-4. §8-5. §8-6. §8-7. §8-8. §8-9. Introduction . ..................... ... ........... 97
Measurement .... ..... ......................... 98
Syntheses ... . ... .. . . ... . . ... ... ... 98
Re-Characterization of Germanium11 Phthalocyanine and Identification of j..l-HydroxygermaniumiYa,�,"f-Triazatetrabenzcorrole ....... . .... ... . . .... ] 00
Characterization of Other Metalloid a,�,"f-Triazatetrabenzcorroles ... ! 04
Decomposition of GermaniumiYa,�,"f-Triazatetrabenzcorrole ................ 1 06 Ring Contractive Reaction Mechanism of GermaniumlYPhthalocyanine ... 1 07 Molecular Symmetry of GermaniumiYa,�,'Y-Triazatetrabenzcorrole ... ! 07
Conclusion ...... . ...... ... ..... . ....................... 112
§8-1 0. References ...................... ll2 CHAPTER 9: CONCLUDING REMARKS ......... . .. . .............. 115
ACKNOWLEDGEMENTS ........................... ...... ..... . . ........... 119
iii
CHAPTER!
OVERVIEWS
§ 1-1. Material Designs of Functional Molecules and Thin Film Preparation Techniques
§ 1-1-1. Functional Organic Materials for Practical Use in Electronics and Photonics A number of organic substances have attracted special interests for application in the field of electronics and photonics, since they possess a variety of unique properties and functions that cannot seen among inorganic materials. Until now, several organic compounds have actually been available as bulk or thin films because of many advantages involving plasticity, flexibility, non-toxicity, chemical reactivity, light
weight, processability, and productivity, in spite of some disadvantages compared to corresponding inorganic materials.
Table 1-1 summarizes the merits and demerits of such functional organic materials compared with alternative inorganic materials. Polyethylene is invariably used as an insulator for coaxial metal wires and cables, due to its flexibility and light-weighr.l-3 Various polymeric resists for microlithography, which exhibit degradation properties under irradiation of ultraviolet (UV) light, electron beam, or X-ray, are indispensable for making fine circuit patterns with micron or sub-micron scales in the large-scale integrate circuits (LSI) technology .I ,2,4-1 0 Poly(vinylidene fluoride) (PVDF) is utilized as an acoustic-electric transducing material, which is applied for headphones, microphones, and hydrophone for use of the computer tomography.1,2,11,12 Poly(methyl methacrylate) (PMMA) exhibiting optical transparency in visible and near infrared (IR) regions is applied to a core material of low-loss optical plastic fibers (OPF) because of an easy handling and low price.l,2, 13-16 A family of liquid crystals serves flat, light-weigh.t, and color displays operated at low electric power.2,17-19 Organometallic compounds em
ployed in the chemical vapor deposition (MOCVD) process are inevitably necessary to fabricate large-area "superlattice" semiconductors that are artificial periodic ultra thin films consisting of GaAs/AlGaAS, ZnS/ZnSe, Si/SiGe, and so on.20,2l Organic photo
conductors (OPC) exhibiting electrophotographic properties, such as poly(vinylcarbazole) and organic pigments, are commercialized as plain paper copiers (PPC) because of non
toxicity and have now over 50% shares in a market of electrophotographics.2,22-25
Recently, many rr-conjugative organic and polymeric solids possessing mobile electrons and higher polarizability have been of particular interest since these have prospect of developing a variety of applications with excellent performances: non-linear
Table 1-1. Merits and Demerits of Functional Organic Materials and Alternative Inorganic Materials.
function
Oelectrical insulator
Odegradation by UV, electron beam, or X-ray
Opiezoelectricity Opyroelectricity
Otransparency in UV, visible, or near IR
organic material inorganic materials Opol yethylene Oceramics Ochloromethylated polystyrene Onovolac resin OSe-Ge
Opoly(vinylidene fluoride) (PVDF)
OPb-La-Zr-Ti
Oxides(PLZT)
Opolymethylmethacrylate (PMMA)
0 ilica
Oliquid crystals
merits Olight-weight Oflexibility 0 lasticit
Odurable to high-voltage Ohigh sensitivity Ohigh contrast Ohigh sensitivity Ohigh contrast Olight-weight Oflexibility
Othin and large area film availability
Omechanical impedance matching with water
Oflexible
Ohigh numeric aperture Olow loss
Otransparent in UV Olight weight
Ocontrol of molecules or Olow electric power
demerit.
Oflammablity
Ofragile
Odry etching durability
Otoxicity
Othin film preparation Olow Curie points
Ofragile
Ohigher loss limit Ofragile
Ocontrast Oresolution
electron by electric field o eration
�---����--- ---
OCRT(cathode ray tube) Ohigh resolution Oheavy weight Odecomposi tion
Ophotoconducti vity
OGa(CH3)3 (TMG) Opol yvin ylcarbazole Ophthalocyani ne
Oamorphous Se Oamorphous Si (a-Si:H)
Ocolorization Olarge-area film Ohandling Onon-toxicity
Ohigher sensitivity in NIR O!ow cost
Ohighest sensitivity in NIR Otoxicity
optical information processing devices,2 6-2 9 conducting materials,30-32 electro
photographic copiers using near IR laser-diodes,22-24 optical information storages with either heat or photon mode, t ,2,22,23 gas sensors,33 electrochromic displays, 18,34,35 rechargeable battery, 36,37 and static charge dissipating materials.38
§ 1-1-2. Fundamental Concept of Molecular Design for Application
In order to advance functional potential of the n-conjugating organic compounds at a practical device level, several requirement must be considered on a molecular level.
2
Table 1-2. Advantages and Disadvantages of Various Preparation Techniques for Thin Films of Organic and Polymeric Materials.
techniques
Langmuir-Blodgett(LB)
casting
chemical adsorption
electrochemical deposition
vapor deposition ion cluster beam (lCB)
chemical vapor deposition (CVD)
type wet
wet wet
wet
dry dry dry
advantage Oultra thin film
Ofilm thickness Ohigh throughput Oeasy processing
Oeasy control monolayer film Oeasy prepare electrically
conducting film
Oeasy control film thickness Ohigh productivity
Ohigh crystallinity Odefect deficient Ohigh productivity Olarge-area film Odefect deficient
disadvantage Olow productivity Ouse f water subphase Opreparation of surface active
material
Ocontrol of film orientation Opreparation of surface active
material
Opreparation of electro
chemically active material Ofilm orientation
Ovolatile material Oexpensive instrument Ovolatile material Ohigh energy or high temperature
First, choice of an organic framework exhibiting high chemical and thermal stabilities is of the primary importance. Second, the organic framework must posses a film forming ability, while maintaining its function. Almost of all the functional materials are usually employed as thin films. Third, the materials must be made up in a desired packing structure and morphology. Organic compounds often ex hi bit polymorphisms in solid and/or in solution. The morphology of the materials, which is affected strongly by chemical and physical treatments, is related significantly to their chemical and physical properties. Next, defect-deficient thin films of organic material should be formed with a desired thickness and preferential orientation on a suitable substrate. Finally, the intended devices consisting of thin films of the functionalized organic materials will be evaluated and judged by customers, in comparison with the alternative inorganic devices.
§ 1-1-3. Thin Film Preparation Techniques
Many preparation techniques of organic thin film have been presented. They can be classified in two categories: the wet and dry processes. Table 1-2 gives the advantages and disadvantages of those methodologies.
The Langmuir-Blodgett (LB) technique, which is one of the casting methods on water with a molecular thickness, is now widely recognized as a fundamental tool for arranging molecules as an ultrathin, well-ordered film, though only surface-active molecules can be used.39-46 The casting methods involving the spin-casting, and dipping
3
technique are commonly used in the fabrication process of polymer films in electrophotography and LSI technology, since the high-quality and large area films with high-throughput can easily be prepared at an ambient condition. 8-10 The chemical adsorption technique is frequently used to control the wettability of surfaces by silane coupling agents.47 The electrochemical polymerization is applicable to electrochemically active molecules but lacks controllability and regularity of the polymers deposited.48,49
On the other hand, the dry techniques basically consist both of evaporation and deposition processes of molecules in an evacuated chamber. All the dry techniques need large-scale equipments consisting of chamber, vacuum pumps, heating boat, and in-situ monitors, unlike the wet techniques. The vapor deposition technique is frequently used for preparation of thin films for thermally stable and evaporable organic materials.SO The ion cluster beam (ICB) technique, which is a modification of the vapor deposition method. is u eful to obtain densely packed and oriented films.SI The chemical vapor deposition (CVD) technique, which involves an introduction of gaseous molecules and the subsequent chemical reaction stimulated by thermal treatment and/or irradiations of high energy such as UV light or plasma, is especially important for preparation of inorganic semiconducting thin films with large area, high-quality, and regulation of the composition.20,50
§ 1-1-4. Molecular Assemblage
Self-assembling phenomena are recognized to be one of the most essential natures in the living and inanimate worlds. Nevertheless, understanding and control of self
assembling nature on a molecular level are still at a rudimentary stage,52,53 except for a few successful studies.
Wegner et al. found that substituted diacetylene derivatives polymerized in solid state and gave a single crystal of the 7t-conjugative polymer.54-56 Schmidt et al.
elucidated a relation between solid-state photoreaction and crystal structure by means of X-ray analysis based on the assumption of topochemical hypothesis in 1964.57 Since a few systematic studies for forced control of molecular packing arrangement had been established, in 1971 Schmidt proposed a crystal engineering concept that manipulate organic crystals and control its chemical reactivity in the solid state by an introduction of specific substituents to the molecules.5 8 From their continuing studies, it was demonstrated that the presence of hydrogen-bonding groups such as primary amides and urethane, dichlorophenyl groups, unsaturated carbonyl, or charge-transfer interaction are the most important factors in the solid-state photochemical reactivity.57-59
Kunitake et al. demonstrated for the first time that some simplified synthetic dialkyl ammonium salts in water for bilayer membranes with vesicle and lamella structures in analogy with the living cells in 1977.60 Since the finding, a relation between
the morphology of the membrane and the molecular tructure of the amphiphiles was intensively studied. The synthetic lipids, which usually contain both of tw hydrophobic long alkyl chains and hydrophilic moiety, form aggregates with bilayer thickness in aqueous media and spontaneously develop higher-order morphological tructures:
globules, vesicles, rods, tubes, disks, and helical superstructures.6l-63 They concluded that these morphologies are primarily related to the surface curvatures of the lipid molecules.
§ 1-2. Historical View of Phthalocyanines and Langmuir-Blodgett Films
§ 1-2-1. Choice of Phthalocyanine and the Langmuir-Blodgett Technique for Application Phthalocyanine and metallophthalocyanine are the 7t-conjugating, planar and robust macrocyclic dyes like porphyrins.64-70 The phthlocyanine structures are exceptionally stable to alkalies, acids, heat, UV light, and electron beam among organic compounds.64-71 In addition, the compounds have been of particular interest in many basic and applied researches because of their versatile chemical and physical properties.
The frameworks can fulfill the first requirement as the functional molecule as mentioned in §l-1-2.
The LB technique provides tailored ultra thin organic films with a molecular size thickness and with a certain orientation on substrates under the conditions of ambient temperature and pressure.42-46 The technique can fulfill the fourth requirement on the functional molecule as mentioned in § 1-1-2.
§ 1-2-2. Phthalocyanines
Figure 1-1 shows the chemical structure of metallophthalocyani ne. Compared with porphyrins, phthalocyanines had received relatively little interest, because researchers other than the phthalocyanine chemists had believed for a long time that phthalocyanines are insoluble in water as well as in organic solvents and are hard to modify their chemical structures. However, recent progresses on chemical modification of the phthalocyanine framework have been remarkable,64,65 because many applied chemists and physicists intend to exploit thin films of robust molecules including phthalocyanine, anthracene, and tetracyanoquinodimethane.
Metal-free phthalocyanine was for the fir t time obtained in 1907 accidentally by Braun and Tcherniac, as a by-product of the preparation of ortho-cyanobenzamide from phthalamide and acetic anhydride.72 Linstead et al. determined the chemical structure of metal-free phthalocyanine and several metallophthalocyanines in 1933.73-77 Robertson et al. confirmed their planarity and dimensions by means of X-ray analysis in 1935.78-82
Figure 1-1. Chemical structure of metallophthalocyanine.
During the 1930s to 1950s, understanding on versatile chemical and physical properties, such as catalytic properties, oxidation and reduction, photoconductivity, X-ray diffraction, ab orption and emi sian spectra and polymorphism were elucidated.65,69 Soluble phthalocyanine was first appeared as sulfonate in the UK patent in 1929.65 Since then, several water and organic solvent soluble phthalocyanines have been demonstrated and patented in the form of quaternary and ternary ammonium salts of pyridyl derivatives of phthalocyanine, sulfur dyes, azo dyes, and leuco dyes.65
In the 1960s to 1980s, further studies on the physical and chemical properties of phthalocyanine solids focu ed on applications to photoconductor,83-87 conductor,88-101 gas sensor, 102-104 multi-colored electrochromic materials, 10 5,10 6 rechargeable battery.107· 108 negative-type patterning materials using electron beam, I 09, I I 0 photochemical hole burning memory, 111 · 112 data storage media using a near JR laser diode (0.78, 0.85 IJ.m region).ll3 Marks et al. reported high electrical conductivity of phthalocyanine that is oxidized with iodine in 1975.88 Since their finding, several conducting phthalocyanines and related polymeric solids appeared, 89-10 I as will be ascribed in § 1-2-2.
Novel phthalocyanine derivatives and their chemical reactivities are recently characterized. Naphthalocyanine as an extended n-electron system of phthalocyanine skeleton was first reported by Mikhalenko et al. in 1969.114,115 Unusual ring contractive reaction of metalloid phthalocyanines by reducing regents which give rise to new tetrapyrrolic macrocycles, triazatetrabenzcorrole, was identified by Fujiki et al. in 1986.116 "A super phthalocyanine" consisting five phthalonitril units was isolated and determined by Marks et al. in 1975.117,118 Self-assembling phthalocyanines containing crown-ether moieties have appeared in connection with ionic transport and recognition of ions by Turkish and Netherlands researchers respectively in 1987-88.119,120
6
§ 1-2-3. The Langmuir-Blodgett Films
Historically speaking, the LB film studie are devided into three important phases of development. In the first stage, pioneering works by Blodgett and Langmuir were published in the 1930s.39-41 They demonstrated that a wide range of materials e. g. long alkyl carboxylic acid, alcohol, and ester, could be deposited as monolayer· at the air
water interface onto solid substrates, although the technique still involved some difficulties concerning control of the deposition proce s. In the second phase. elegant works were achieved by Kuhn et al. in the 1960s.43, 121-123 They elucidated energy transfer phenomena in the interlayer and the intralayer of built-up films using amphiphilic chromophores with proper monolayer manipulation. The third development started in the 1 980s.44-46 New potential applications of built-up films were opened in the field of microlithography, integrated and nonlinear optics, information torage using photochromism and thermochromism, gas sensors, low-dimensional conductors, and insulator. Such applied researches were stimulated by the concept on "Molecular electronic devices" proposed by Carter in 1982.124
Figure 1-2 illustrates a typical surface pres ure-area isotherm of fatty acid on water subphase. When a solution containing fatty acid is spread and the resulting monolayer is compressed, the isotherm normally contains four stages: gas-like. expanded (liquid-like), condensed, and collapsed phases. In the gas-like phase I, fatty acid molecules float on the water as an isolated molecules or as small ·ize islands. In the expanded or liquid-like phase II, the small island coalesce to larger island . In the condensed phase III, the islands are completely joined in the form of multi-crystals including several boundaries with monolayer thickness. The multi-crystals eventually collapse via 1tc.
There are two typical techniques of obtaining built-up films. One is the conventional vertical dipping technique invented by Blodgett39-41 and the other is the horizontal lifting method demonstrated by Fukuda et al. 125
The former is basically composed of three tages and is illustrated in Figure 1-3:
(a) a solution containing materials is first spread on a water surface.
(b) a mobile monolayer on water is compressed to eliminate voids.
(c) a solid multilayer film is then built up by repeated immersion of a substrate into the water.
In the conventional technique, if a monolayer is deposited on a substrate only in a downstroke of the substrate, the built-up film is called as a "x-type" film. If a monolayer is deposited only in an upstroke, a "z-type" film is obtained. When a monolayer is deposited in both of the upstroke and downstroke processes, the built-up film is named as a "y-type" film. Figure 1-4 illustrates the three patterns of the deposition processed and the built-up films.
7
'E z E
0
IV. COLLAPSED PHASE
III. CONDENSED PHASE
.-J
I.GAS-LIKE PHASE TI. EXPANDED (LIQUID-LIKE)
PHASE
l l
AREA, A I A �molecule·1
Figure 1-2. Typical force-area isotherm of fatty acid on water subphase.
TROUGH
Figure 1-3. Schematic view of the vertical dipping technique of obtaining Langmuir-Blodgett built-up film.
(a)
·�-
. -----
--..- - �i
(b)
(c)
down stroke up stroke film type
Figure 1-4. Three patterns of the Langmuir-Blodgett built-up films through immersion of a substrate. (a) x-type films; (b) y-type films; (c) z-type films.
SUBSTRATE
MOVING BARRIER
-BARRIER
PRESSURE �
i _..
al.U1LlllJ1 L UUL!JJUlllJL1Ll!
•( ) ---
-
(ii)
(iv)
Figure l-5. Schematic view of the horizontal lifting technique of obtaining Langmuir-Blodgett built-up film.
In contrast, the latter technique requires some tricky procedures to obtain a good quality film. Figure 1-5 displays a schematic view of the horizontal lifting technique, (a) a compre ed monolayer on water is prepared.
(b) one face of a substrate is kept parallel to the water surface and comes into contact with the monolayer under a constant film pressure.
(c) a new barrier is put on the monolayer at the left side closely adjoining the substrate and then a right-side barrier of the substrate is removed.
(d) the substrate is slowly lifted up from the water surface.
By repeating these procedures, the multilayers which correspond to "x-type" films by the conventional LB method are prepared.
§ 1-2-4. Phthalocyanine Langmuir-Blodgett Films
Studies on the LB films consisting of phthalocyanines have been less active than those on other functional materials. This may be attributed to a preconception that the phthalocyanines cannot produce built-up films, since the phthalocyanines are immiscible in all common organic olvents and the molecular shape is quite different from the conventional fatty acids.
Alexander conducted a pioneering study on force-area isotherms of unsubstituted metal phthalocyanines in 1937.126 In 1983, Roberts et al. examined the possibility of the built-up films and the electrical properties for both unsubstituted metal-free phthalocyanine and soluble copper tetra(tert-butyl)phthalocyanine, in which metal-free phthalocyanine was produced by hydrolysis of dilithium phthalocyanine at the water-air . mter ace. f 127 Snow et al. demonstrated m 1984 the surface 1sotherms and self-assembling . . properties of several oluble metal phthalocyanines with phenoxy substituents.128 Their successful studies in the early 1980s invoked many researches on the LB films consisting of a variety of soluble phthalocyanines. Until now. over 30 papers on the phthalocyanine LB films have appeared.127-146
§ 1-3. Purpose and Contents of the Present Thesis
A variety of molecular approaches have been attempted for a construction of one
dimensional phthalocyanine conductors so far. The phthalocyanines containing metalloids, first-row transition metals, and rare-earth metals can provide one-dimensional conductor , whose stacking structures are controlled by covalent linkage (0, F, S, and organic ligands),90-96 by the out-of-plane structure of the central metals,97,98 and by long chain alkyl peripheral substituents.99 Unfortunately, these phthalocyanines seem not to form LB films because of extremely low solubilities and the lack of hydrophilic moieties.
10
Among the one-dimensional phthalocyanine assemblies mentioned above, Marks et al. systematically examined the relationship between electrical conductivity and interplaner separation for a series of 0-linked, one-dimensionally stacked co facial phthalocyanine assemblies that are oxidized with iodine. They concluded that phthalocyaninc molecules must be arranged in as close spatial proximity a po sible to obtain higher conductive state.88-91 The e polymers are obtained by dehydration of 1.1- dihydroxy metalloid phthalocyanine (metalloid = Si, Ge, and Sn) in olid tate, and are quite immiscible in organic solvents, except for in concentrated sulfuric acid, and lack the LB film forming ability.
Main subjects of the present thesis are to construct one-dimensional phthalocyanine assemblies and to control its conductivity in the LB film.
In Chapter 2, self-a sembling features of the alkylamide ubstituted nickel(II) phthalocyanines in cast film, in solid, and even in solution are discussed using a modified molecular exciton theory _147-150 New phthalocyanines were designed based on the following ideas. If four secondary amides are symmetrically substituted on each of the peripheral position of phthalocyanine ring, the most favorable structure is expected to form one-dimensionally stacked arrays resulting from directional hydrogen-bonding forces of the amide units and strong van der Waals' stacking forces of phthalocyanine rings. Also, introduction of the flexible and hydrophilic n-octadecylamide moieties leads to increased solubility and afford the capability to form the LB film.
In Chapter 3, characterization of the LB films of soluble nickel phthalocyanines is discussed.144 The phthalocyanines gave built-up films with one-dimensional stacking structures, while maintaining their assembling structures in chloroform solution. In-plane dichroisms were also invariably observed in the UV -visible and infrared regions. The origin of the dichroisms is discussed. Molecular arrangement and orientation of the phthalocyanine assemblies are proposed.
In Chapter 4, applications of thin films consisting of the soluble nickel phthalocyanines are demonstrated in terms of fine patterning and electrical properties.109,110 The film conductivities increased by 2 to 4 orders of magnitudes upon exposure to iodine vapor. The films exhibited negative patterning features to electron beam dose and excellent resistance to plasma-assisted etching.
In Chapter 5, facile synthesis of soluble metal phthalocyanines including short and compact alkyls and/or cyano moieties is reported. lSI Metal-free and metal tetra(tert
butyl)phthalocyanines were obtained in only two to three steps from alkylbenzene starting materials, whereas a previous procedure required seven steps.1 52 The phthalocyanines including four alkyl groups and four cyano groups are newly prepared for the purpose of controlling both highest occupied and lowest unoccupied energy levels in solid films.
II
In Chapter 6, characterization of the LB films of lightly substituted phthalocyanines is presented. l43,153 The phthalocyanines can be dissolved in organic solvent as monomeric dispersion and the one-dimensional phthalocyanine assemblies are formed in the LB films and in powders. Molecular arrangement and orientation of the phthalocyanine assemblies are discussed.
In Chapter 7, the electrical properties of the LB films of the lightly substituted phthalocyanines are examined. 143 In-plane electrical conductivities of undoped LB films of the phthalocyanine containing both alkyl and cyano groups are highly sensitive and reversible. The film conductivity increases steeply by five orders of magnitude, when the film is exposed to active gases such as iodine, triethylamine and n-butanethiol.
Conductivity responses of the phthalocyanine LB films to these gases are expllcable in terms of ionization potentials and electron affinities of the films.
In Chapter 8, a new tetrapyrrolic macrocycle: a,�,y-triazatetrabenzcorrole is described. 1 16 It was characterized by means of elemental analysis, spectral measurements (mass, UV -visible, IR, and I H NMR), chemical reactivity, and oxidative titration results. This compound was reported previously as a divalent germanium phthalocyanine (Ge11Pc).154 The finding was initiated based on the idea that the divalent germanium phthalocyanine may form a one-dimensional Ge linear polymer. ISS
In Chapter 9, summary and some concluding remarks are included.
§ 1-4. References
I. Furukawa, J. Kobunshi Shinzairyo (New Functinal Polymeric Materials) Kagaku Dojin, Kyoto, 1987.
2.
3.
4.
5.
6.
7.
8.
9.
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18
CHAPTER2
SELF-ASSEMBLING PHENOMENA OF NICKEL
PHTHALOCY ANINES SUBSTITUTED WITH ALKYLAMIDES
SYNOPSIS
Two new types of highly soluble nickel phthalocyanines containing four octadecylamides (AmPc1 and AmPc2) have been prepared. Both the AmPcl and AmPc2 derivatives are predicted to form one-dimensionaL self-assembled structures with van der Waals' thickness. This results from the hydrogen-bonding force of the secondary amides in solid, in cast film, and in solution and is evident from visible and emission spectra and the X
ray diffraction data. The assembling numbers in AmPc I and AmPc2, which strongly depend on the condition of the solution, are evaluated as 5 -18 for AmPc 1 and 2 - 5 for AmPc2 using a modified molecular exciton theory.
§2-1. Introduction
Phthalocyanines (Pc's), which exhibit high chemical and thermal stabilities among organic compounds, have been of particular interest in many fields of basic and applied research I-4 concerning catalysts, 1.2 solar cells, 6.7 photosensitizers,8-l 0 low-dimensional metals, 11-20 ga sensors,21,22 electrochromism,23,24 lithium batteries,25,26 electron beam negative resists,27.28 photochemical hole burning memories,29 and molecular electronic devices.30 However, unsubstituted Pc's generally have some limitations in arranging and organizing the Pc moieties in a desired crystal structure and thickness on solid substrates, because the Pc's usually exhibit polymorphism in the solid state and extremely poor solubilities in common organic solvents.
One of our main interests involves how to control the lattice architecture and electronic delocalization of films prepared by spin cast and Langmuir-Blodgett (LB) techniques for microelectronic devices based on organic substances. For this purpose, several requirements will exist. First of all, the Pc's should be soluble in a suitable solvent.
A second important requirement is that the Pc's should be arranged in a one-dimensional (1- D) linear stack with van der Waals' thickness and arrayed in a preferential orientation on a suitable solid substrate.
A variety of molecular approaches has been attempted for the construction of 1-D Pc conductors.II-20 The Pc's containing group 13 and 14 metalloids,l3-16,18 first-row transition metaJs11,12,17 and rare-earth metals19 can provide 1-D conductors, whose stacking structures are linearly controlled by covalent linkage (0, F, S, and organic ligands) and by the out-of-
19
plane structure of the central metals. Unfortunately, these Pc's seem not to form spin cast and LB film because of their extremely low solubilities.
As our first attempt to obtain highly soluble 1-D Pc self-assemblies having spin cast and LB film forming ability, two new nickelphthalocyanines with four octadecylamide substituents (See Figure 2-1, abbreviated as AmPc I and AmPc2, respectively) have been synthesized based on the following ideas: If four secondary amides are symmetrically substituted to each of the peripheral position of Pc ring. the most favorable structure is expected to be in 1-D stacked arrays resulting from directional hydrogen-bonding forces of the amide units and intense van der Waals' stacking forces of Pc rings. In addition, introduction of the flexible and hydrophilic n-octadecylamide moieties will help to increase solubility and afford the ability to form LB films of the Pc's assemblies. In biological systems, the secondary amides are well known to play an important role in fixing the functional moieties into a specific conformation through the directional hydrogen bonding forces, uch as a-helix and �-sheet in proteins and base-pairings in nucleic acids.
In this chapter, we discuss self-assembling features of AmPcl and AmPc2 in the solid, in the cast films, and in the solutions using a modified molecular exciton theory.
§2-2. Chemical Structure of Phthalocyanines with Alkylamide Substituents
Both the AmPc I and AmPc2 molecules possess the so-called degenerate Q-bands originating from n-n* transitions. These bands are comprised of M and L transitions with the same energies and oscillator strengths along the Pc ring,2 as shown in Figure 2-1.
Accordingly, the characteristic Q-bands are considered as a sensitive probe for discussing the self-assembling features and for characterization of AmPc I and AmPc2 in solution and in cast films from their electronic absorption spectra.
§2-3. Electronic Absorption Spectra of the Phthalocyanine Assemblies
Figures 2-2 and 2-3 illustrate electronic absorption spectra and their second derivative spectra for AmPc 1 and AmPc2 in chlorobenzene solution and in cast films from CHCl3 solution. Figure 2-4 shows electronic absorption and emission spectra of the monomeric state of highly soluble tetra(tert-butyl)PcNi (Ni(TBP)) in CHCl3 solution.
For the respective AmPcl and AmPc2 derivatives, the shape of the Q-bands in solution resembles the Q-bands in the films. This indicates that the basic assembling structures for AmPc1 and AmPc2 in solution are similar to those in the films.
The Ni(TBP) monomer in solution has a sharp Q(0'-0") band at 670 nm with a width of 450 cm-1 at half height. In contrast, the Q-bands of the AmPc 1 and AmPc2, both in the cast film and in solution, are comprised of intense main Q-bands located at ca. 605-630 nm and weak satellite Q-band located at ca. 680 nm. The absorption maxima (Arnax) for the main
R R
R = -C(=O)NHC1gH37 (AmPcl) R = -NHC(=O)C1gH37 (AmPc2) R
M
Figure 2-1. Molecular structures and their abbreviations of new soluble nickel phthalo-cyanines substituted with four long alkyl chain secondary amides. M andL stand for Q-band transition, respectively.
Q-bands of both AmPcl and AmPc2 are strongly blue-shifted by ca. 70 nm and broadened by 1770 cm-1 for AmPcl and by 2680 cm-1 for AmPc2. when compared to the Arnax of the Ni(TBP) monomer Q-band. When the solutions are changed from hot diluted solutions (1 o-s M at 80 OC) to concentrated solutions (I o-3 M at room temperat ure), the Arnax values in the main Q-bands are blue-shifted by ca. 4 nm for AmPc 1 and by 20 nm for AmPc2. and the satellite Q-bands intensities decrease for both.
Such broadening and blue-shifts in the Q-band spectra for both AmPc 1 and AmPc2 seem to be characteristic of the Q-band spectra of 1-D linearly stacked Pc polymers with van der Waals' thickness, such as 0-linked tetra(tert-butyl)PcM polymer ((TBPMO)n),40 0- linked PcM polymer ((PcMO)n), 13.14 and F-linked PcM' polymer ((PcM'F)n) (M = Si, Ge and M'=Al, Ga).l5,4I In these Pc polymers. the Q-bands are strongly blue-shifted by ca. 30 - 70 nm (600 _ 700 cm-1) and exhibit broadening when compared with the corresponding monomer Q-bands. The Q-band spectra of well-defined Pc oligomers have also been reported. The (PcSi)20 and (PcGe)20, which are linearly assembled Pc dimers having van der Waals' thickness, are blue-shifted by 840 and 870 cm-1 from the corresponding PcSi and PcGe monomer Q-bands. respectively.42.43 In a series of the 0-linked PcSi 1-D oligomers ((PcSiO)n, n means the association number) the Q-band spectra, with increasing n from 1 to 4, have been reported to be blue-shifted, decreased in extinction coefficient, and broadened markedly.43 In contrast, f3-PcCu and �-PcH2 thin films existing in obliquely
