Squaraines polymers

The adsorbed polymer sterically stabilizes particles of 1 in polymer solution, resulting in a stable squaraine-polymer dispersion Analogous steric stabilization of pigment particles via specific... 

In summary, the stabilization mechanism of squaraine particles in organic solvents has been understood as a steric stabilization process by spectroscopic technique. The knowledge gained in this work has enabled us to formulate other stable squaraine-polymer dispersions using polymers other than poly(vinylacetals). 

Dyes such as erythrosin B [172], eosin [173-177], rose bengal [178,179], rhodamines [180-185], cresyl violet [186-191], thionine [192], chlorophyll a and b [193-198], chlorophyllin [197,199], anthracene-9-carboxylate [200,201], perylene [202,203] 8-hydroxyquinoline [204], porphyrins [205], phthalocyanines [206,207], transition metal cyanides [208,209], Ru(bpy)32+ and its analogs [83,170,210-218], cyanines [169,219-226], squaraines [55,227-230], and phe-nylfluorone [231] which have high extinction coefficients in the visible, are often employed to extend the photoresponse of the semiconductor in photoelectro-chemical systems. Visible light sensitization of platinized Ti02 photocatalyst by surface-coated polymers derivatized with ruthenium tris(bipyridyl) complex has also been attempted [232,233]. Because the singlet excited state of these dyes is short lived it becomes essential to adsorb them on the semiconductor surface with... 

Molecular complexes, such as the complex formed between poly(N-vinylcaibazole) and 2,4,7-trinitro-9-fluorenone, and dye-polymer aggregates were widely used as generation materials in many early applications. Since these materials are not infrared sensitive, there has been increasing emphasis on pigments. The more widely studied are various azo, phthalocyanine, squaraine, and peiylene diimide derivatives. A common feature of all of these materials is that they are polymorphic and exist in many different crystal forms. The properties are thus very sensitive to the conditions used in their preparation. Further, the sensitivity of these materials is strongly field dependent as well as dependent on the transport material. For a review of generation materials, see Law (1993). 

Its Relationship with the Stabilization Mechanism of Squaraine Particles in Polymer Solutions... 

Three emission bands (a, p and y in the order of decreasing energy) are observed in CH2CI2 solution and are found to be the emission from the excited state of 1, from the excited state of a solute-solvent complex and from a relaxed twisted excited state of the solute-solvent complex, respectively. Model compound studies show that squaraine forms strong solute-solvent complexes with alcoholic solvent molecules. Analogous complexation process between 1 and the OH groups in PVF is also shown to occur. A model for the stabilization of particles of 1 in polymer solution is put forward where we propose that the stabilization mechanism is a steric effect achieved by adsorption of PVF macromolecules onto particles of 1 via the formation of the PVF 1 complex. 

Here we report preliminary results on the multiple fluorescence emission of 1 and 2. From structure-property relationships, solvent effect and temperature effect studies, we are able to show that the multiple emission is from the emission of free squaraine in solution, the emission of the solute-solvent complex and the emission of a twisted relaxed excited state. Further solvent effect study using 2 as a model shows that squaraine forms strong solute-solvent complexes with alcoholic solvent molecules. Analogous complex-ation process is also detected between 1 and the hydroxy groups on the macromolecular chains of poly(vinyl formal). The Important role of this complexation process on the stabilization mechanism of particles of 1 in polymer solution is discussed. 

Squaraines 1 and 2 were synthesized from squaric acid and N,N-dialkylaniline derivatives using the procedure described by Sprenger and Ziegenbein (4). Poly(vinyl formal), PVF, formal content 82JS, acetate content 12X, hydroxy content 5, was purchased from Scientific Polymer Products Inc. Solvents were spectro grade from Fisher and were routinely stored over 3A molecular sieves before use. Fluorescence spectra... 

The absorption and emission properties of bis[4-(dimethylamino)-phenyljsquaraine (3), bis[4-(dimethylamino)-2-hydrox5q)henyl]squaraine (21), bis(2,4,6-trihydroxyphenyl)squaraine (18), and an a2ulyl derivative of squaraine in poly(methyl methacrylate) and polystyrene have been reported [73]. The fluorescence lifetimes of new nanoseconds were observed for 3 and 21 in the polymer films, whereas for 18, the fluorescence lifetime was much shorter (10 ps). As discussed above, the neutral form of 18 is relatively nonfluorescent. A rapid excited state proton transfer tautomerization or deprotonation was proposed for the rapid deactivation of the excited state of 18. 

Vauthey et al. [132,133] have examined the hole-burning mechanisms of a few squaraine dyes in hydrogen-bonding and non-hydrogen-bonding polymers. In these cases, the spectral holes were not persistent, and decay with distribution rates ranging from 10 s to about 1 s" [132,133]. 

Figure 6.12 (a) Sensing of pH using the pH-sensitive squaraine dye conjugated to CdSe/ ZnS QDs modified by an amphiphilic polymer associated with the hydrophobic nanocrystals (b) Fluorescence spectra of the dye-modified... 

Polysquaraines, also known as wide absorption spectrum squaraines, are currently under development. The optical properties of these systems are ideal for a variety of optical-electronic materials, such as squaraine-based near-infrared dyes, low-band gap polymers, and cation sensors however, these compounds are difficult to solubilize and process [73]. 

Figure 10J2. (a) A plot of log 0.5 vs Ip (CGL Chloiodiane Blue/binder, CTL hole transporting molecules of varying ionization potential (p) (b) A plot of log Eq.s vs. Eqx (CGL squaraines of varying oxidation potential, CTL a triarylamine in a polycarbonate polymer). (Part (a), reproduced fk>m ref. 323, Copyright 1981, IEEE Industry Applications Association.)... 

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