Squarylium dye

Nakazumi H, Natsukawa K, Nakai K, Isagawa K (1994) Synthesis and structure of new cationic squarylium dyes. Angew Chem Int Ed Engl 33 1001-1003... 

Kim SH, Hwang SH (1997) Synthesis and photostability of functional squarylium dyes. Dyes Pigm 35 111-121... 

Yagi S, Nakazumi H (2008) Squarylium dyes and related compounds. In Gupta RR, Strekowski L (eds) Topics in heterocyclic chemistry, vol 14, Springer. Berlin, Heidelberg, pp 133-181... 

Yagi S, Hyodo Y, Matsumoto S, Takahashi N, Kono H, Nakazumi H (2000) Synthesis of novel unsymmetrical squarylium dyes absorbing in the near-infrared region. J Chem Soc Perkin Trans 599-603... 

Yan W, Sloat AL, Yagi S, Nakazumi H, Colyer CL (2006) Protein labeling with red squarylium dyes for analysis by capillary electrophoresis with laser-induced fluorescence detection. Electrophoresis 27 1347-1354... 

Nakazumi H, Colyer CL, Kaihara K, Yagi S, Hyodo Y (2003) Red luminescent squarylium dyes for noncovalent HSA labeling. Chem Lett 32 804-805... 

Yan W, Colyer CL (2006) Investigating noncovalent squarylium dye-protein interactions by capillary electrophoresis-frontal analysis. J Chromatogr A 1135 115-121... 

Sloat AL, Roper MG, Lin X, Ferrance JP, Landers JP, Colyer CL (2008) Protein determination by microchip capillary electrophoresis using an asymmetric squarylium dye noncovalent labeling and nonequilibrium measurement of association constants. Electrophoresis 29 3446-3455... 

Yagi S, Ohta T, Akagi N, Nakazumi H (2008) The synthesis and optical properties of bis-squarylium dyes bearing arene and thiophene spacers. Dyes Pigm 77 525-536... 

Kim SH, Kim JH, Cui JZ, Gal YS, Jin SH, Koh K (2002) Absorption spectra, aggregation and photofading behaviour of near-infrared absorbing squarylium dyes containing perimidine moiety. Dyes Pigm 55 1-7... 

On the other hand, squarylium dyes have an interesting chromophore which are... 

T. Mori, K. Miyachi, T. Kichimi, and T. Mizutani, Electrical and luminescent properties of color-changeable organic electroluminescent diode using squarylium dyes, Jpn. J. Appl. Phys., 33 6594-6598 (1994). 

A similar sharp red emission exhibit squarylium dyes like the squarylium cyanine dye 64, which emits 650nm [152]. Unfortunately, the Stokes shift is rather small, which leads to high reabsorption. A number of other red emitting dyes have been exploited as well [153-156]. 

F. Weleder, B. Paul, H. Nakazumi, S. Yagi and C.L. Colyer, Symmetric and asymmetric squarylium dyes as noncovalent protein labels a study by fluorimetry and capillary electrophoresis. J. Chromatogr.B, 793 (2003) 93-105. 

Wide variation of the donor gronps on the squarylium dyes of structure type (4.6) only gave a maximnm wavelength of absorption of 708 mn, and it was necessary to nse the strongly electron-donating dihydroperimidine ring system to achieve absorption fully into the near-IR, as exemplified by (4.8), 800-810 nm, 150 000. °... 

Ketene trimer can be recovered from the tarry residue of diketene distillation and converted into valuable building blocks like 1,3-cyclobutanedione and squaric acid [2892-51-5] (140,141), an important intermediate in the synthesis of pharmaceuticals and squarylium dyes used in photostatic reproduction (142,143). 

X(3) values for several azo dyes at 633 nm and for a squarylium dye at 7 9 9 nm dispersed in Poly(methylmethacrylate) glasses, and compare the results (obtained by electrooptic methods) to those for a model poly(thiophene) and a poly(diacetylene).(147)... 

Somewhat related to the (cationic) cyanines are the squarylium dyes which are overall charge neutral species derived from squaric acid. They are easily prepared, have high molar absorptivities (>100,000), but typically are unstable to hydrolysis in dipolar aprotic solvents. They are characterized by a sharp strong absorption which lies at wavelengths longer than 640 nm, with no other identifiable electronic transitions in the visible (Figure 2). The vibronic structure of these dyes may show only one shoulder corresponding to a reasonable value for a C-C or C-0 stretch. We were able to systematically vary the structure of a series of squarylium dyes in order to test assumptions about the structure-property relationship for minimization of the residual absorption. 

Figure 2. Structure and spectral properties of squarylium dyes synthesized in this work.

Note that the squarylium dye, 9, has quite a large susceptibility. At 1% in PMMA, the bulk susceptibility is 13x10 14 m(18). At a hypothetical "100%", this susceptibility is comparable to the THG and DFWM susceptibilities of some polydiacetylenes, though this comparison must be viewed with some circumspection considering the difficulty in accounting for the differences in dispersion between different processes. 

Squarylium dyes such as (83) [75] have probably received less attention than cyanine dyes due to the fact that the majority of syntheses furnish symmetrical species which are difficult to monofunctionalize in reactions such as the formation of peptide conjugates. The unsymmetrical types have been reported but seem to suffer from about 50% decrease in extinction coefficient. Squaiyliums are also more difficult to handle due to their low solubility. Very few water-soluble systems have been reported. These compounds are also used exclusively as fluorophores, but quantum yields are highly dependent on substituents and environment. 

In numerous patents the synthesis of suitable furo-, thieno-, and pyrrolo-tropylium salts is described, for example, that of squarylium dyes like 623 and 624 (Scheme 169 85JAP60/262163 86JAP61/185487 88JAP63/41858, 88JAP63/102990). These substances serve as components of photoconduc-tive thin layers for electrophotographic photoreceptors. The materials are claimed to exhibit increased sensitivity, stability on storage, and durability to laser-beam reading. 

Squaraines are derivatives of 3,4-dihydroxycyclobut-3-ene-l,2-dione, or squaric acid, so called because the central structural motif consists of four carbon atoms linked to form a square [8], Numerous squarylium dyes, such as those in Fig. 6.8,... 

Among the materials for laser printer utilization, we may consider squarylium dyes and trisazo compounds (Fig. 5). Squaraines, for instance, give rise to photoreceptors with superior electrical characteristics, as they can form different crystalline modifications throughout the introduction of suitable impurities at low concentration [42]. This characteristic is due to the ability of squaraines to form aggregates having very broad absorption spectra (400 to 1000 nm). 

It is of interest to note that another similar squarylium dye 3-XXV has also been shown to concomitantly crystallize in a green monoclinic phase and a purple triclinic phase (Ashwell etal 1996). The structurehas been reported for the former, but crystals of the latter were not of sufficient quality to determine the crystal stmcture. 3-XXV... 

The hemicyanine 159 was prepared from the salt 77-1 according to Equation (25) <2000JHC1321>. Moreover, the series of cyanine, merocyanine, and squarylium dyes 160-165 was prepared. 

---