Diacetylene multilayer

In course of subsequent work Bubeck, Tieke, and Wegner discovered that the action spectrum for photopolymerization of undoped diacetylene multilayers extends into the visible provided some polymer formed in course of previous UV-irradiation is present. Since obviously excitation of the polymer can sensitize the reaction this effect has been termed self-sensitization. Checking the absorption spectrum of the polymer produced via self-sensitization assured that the final product is identical with the product obtained under UV excitation of the monomer. Later work by Braunschweig and Bassler demonstrated, that the effect is not confined to multilayer systems but is also present in partially polymerized single crystalline TS-6, albeit with lower efficiency. Interestingly, the action spectrum of self-sensitization follows the action spectrum for excitation of an electron from the valence band of the polymer backbone to the conduction band rather than the excitonic absorption spectrum of the polymer which is the dominant spectral feature in the visible (see Fig. 21). The quantum yield is independent of the electric field, whereas in a onedimensional system the yield of free carriers, determined by thermal dissociation of optically produced, weakly bound geminate electron-hole pairs, is an linear function of an applied electric field 29.30,32,129) Apparently, the sensitizing action does not... 

Table 3. List of dyes used as sensitizers for photopolymerization of diacetylene multilayer assemblies. (R —(CH2)S- CH3 the counterion was I ) and their absorption maxima...

The photopolymerization of diacetylene and related crystalline systems continues to attract strong interest. The photopolymerization of diacetylene multilayers has been found to be sensitized to visible light on incorporating... 

Chemical properties of deposited monolayers have been studied in various ways. The degree of ionization of a substituted coumarin film deposited on quartz was determined as a function of the pH of a solution in contact with the film, from which comparison with Gouy-Chapman theory (see Section V-2) could be made [151]. Several studies have been made of the UV-induced polymerization of monolayers (as well as of multilayers) of diacetylene amphiphiles (see Refs. 168, 169). Excitation energy transfer has been observed in a mixed monolayer of donor and acceptor molecules in stearic acid [170]. Electrical properties have been of interest, particularly the possibility that a suitably asymmetric film might be a unidirectional conductor, that is, a rectifier (see Refs. 171, 172). Optical properties of interest include the ability to make planar optical waveguides of thick LB films [173, 174]. 

If these materials are deposited as LB multilayers, polymerization can be induced either by thennal or optical means. This subject has been intensively studied [95, 96, 92, 98 and 99]- Since parameters such as m, subphase components, pH and polymerization before and after dipping, as well as temperature and wavelength employed for polymerization can be varied, the literature on diacetylenes is extensive and the reader is referred for example to the book of Tredgold [1001. 

Tieke B, Graf H J, Wegner G, Naegele D, Ringsdorf H, Baner]ie A, Day D and Lando J B 1977 Polymerization of mono- and multilayers forming diacetylenes Coiioid Poimer Soi. 255 512-31... 

Studies of the solid state photopolymerization of deposited multilayer films reveal that uv induced photopo1ymerizati0n of disubstituted diacetylenes... 

Monolayer Polymerization. Polymerization of the highly ori-ented monomer films can simply be achieved by UV irradiation under nitrogen (Figure 8.). The polymerization of the diacetylene monomers (2, 5-9) is a topochemical reaction (32,38) that only takes place, if the monomers are perfectly orderecTT i.e. in the crystalline state or in oriented mono- (32) or multilayers (39) and leads to the formation of conjugated Tlue and red colorecT polymer backbones (Eqn. I.). 

Thin films of materials play an important role in modern electronics. Langmuir-Blodgett films (Mort, 1980) are prepared from surface-active molecules that adsorb at the surface of an aqueous solution. The surface is gently compressed to produce a close-packed monolayer, which can be coated on appropriate substrates by dipping at constant surface pressure. The layers so produced are of a precise thickness, and repeated dipping gives multilayers. For example, diacetylenes and other polymerizable... 

Fig. 20. Comparison between UV-absorption spectra of a paraffinsubstitiled diacetylene (m = 8, n = 8) incorporated in a multilayer assembly and the action spectrum of photopolymerization (from Ref.

The range of potential sensitizers for photopolymerization of diacetylenes widened considerably when Wegner and coworkers discovered sensitized photopolymerization in LB-multilayer systems doped with certain dyes. It is known for long that dye molecules carrying long aliphatic substituents can easily be incorporated into LB-multilayer assemblies without destroying the sample architecture Therefore, the topotactic requirements for the polymerization reaction to proceed are retained. 

Molecular interactions between D-glucolipids and multilayered vesicles were also demonstrated with partially polymerized diacetylene units. Red vesicles constructed by sonication and subsequent UV irradiation formed a red precipitate with Con A which was redissolved by methyl-D-mannopyranoside to regenerate a red solution . ... 

The outline of this article is as follows. After general remarks tUsout the solid-state polymerization process, adopting the view that it is important to develop new types of solid-state polymerization, the polymerization of the following classes of monomers will be discussed diacetylenes, monoacetylenes, vinyl and diene monomers, cyclic systems which ring open, and transition metal systems. It is implicit in the discussion that appropriately substituted forms of the above monomers may be polymerized as mono-layers and multilayers (11-13) as well as in the form of inclusion complexes (14). Emphasis will be placed on topics of current interest. 

Tieke B and Weiss K 1984 The morphology of Langmuir-Blodgett multilayers of amphiphilic diacetylenes—effects of the preparation conditions and the role of additives J. Colloid Interface Sol. 101 129-48... 

B. Tieke, H.-J. Graf, G. Wegner, B. Naegele, H. Ringsdorf, A. Banerjie, D. Day, and J. B. Lando, Polymerization of mono- and multilayer forming diacetylenes. Polymer Science. Pofymere. 255 36 (1977). 

H. Schapp, B. Hupfer, R. A. van Wagenen, J. D. Andrade, and H. Ringsdorf, Surface characterization of functional poly (diacetylene) and poly (butadiene) mono- and multilayers. Colloid and Polymer Science 260 262 (1982). 

Molecules 19-22 are model systems for a related project, which aims to incorporate D-a-A systems into LB-film-forming diacetylenes, which may be polymerized in situ on the film balance, for the purpose of preparing new systems with promise as non-linear optical devices. Interestingly, 19-22 form Z-type multilayers on a glass substrate (the film subphase is held at 5° C but the slide is at room temperature). An attempt was made to see whether any second harmonic signals could be detected from Z multilayers of 21, but the result was negative [47]. 

A modification of the sequential polyelectrolyte multilayer fabrication strategy uses small molecule bipolar amphiphiles in place of polymers [53,74-76]. Many tens of layers of small molecules can be stacked by alternate adsorption, approaching total layer thicknesses between 150 and 200 nm. Organization in these multilayers is reduced over that observed in polyelectrolyte multilayers. This order as well as stability can be improved by hybrid structures comprising alternating bipolar am-phiphile and polyelectrolyte charged layers [53], Bipolar diacetylenes can also be utilized [77, 78], providing interlayer stabilization via photopolymerization after multilayer assembly. 

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