Squarylium

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... 

Lin T, Peng BX (1997) Synthesis and spectral characteristics of some highly soluble squarylium cyanine dyes. Dyes Pigm 35 331-338... 

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... 

Ioffe VM, Gorbenko GP, Deligeorgiev T, Gadjev N, Vasilev A (2007) Fluorescence study of protein - lipid complexes with a new symmetric squarylium probe. Biophys Chem... 

Song B, Zhang Q, Ma WH, Peng XJ, Fu XM, Wang BS (2009) The synthesis and photostability of novel squarylium indocyanine dyes. Dyes Pigm 82 396-400... 

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... 

Ioffe VM, Gorbenko GP, Tatarets AL, Patsenker LD, Terpechnig EA (2006) Examining protein-lipid interactions in model systems with a new squarylium fluorescent dye. J Fluoresc 16 547-554... 

Reis LV, Serrano JP, Almeida P, Santos PF (2009) The synthesis and characterization of novel, aza-substituted squarylium cyanine dyes. Dyes Pigm 81 197-202... 

Negres RA, Przhonska OV, Hagan DJ, Van Stryland EW, Bondar MV, Slominsky YL, Kachkovski AD (2001) The nature of excited-state absorption in polymethine and squarylium molecules. IEEE J Sel Top Quantum Electron 7 849-863... 

Santos PF, Reis LV, Duarte I, Serrano JP, Almeida P, Oliveira AS, Vieira Ferreira LF (2005) Synthesis and photochemical evaluation of iodinated squarylium cyanine dyes. Helv Chim Acta 88 1135-1143... 

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

Figure 16. Reversible change of monolayer spectra among J-, H-aggregates and monomeric species of squarylium with four butyl groups by compression.

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. 

The squarylium (4.6) and croconium (4.7) dyes are closely related structurally to cyanines but are in fact donor-acceptor molecules and consequently the design principles of near-IR absorbers based on these chromophores are different. The synthesis of these chromophores is achieved easily by reacting either squaric acid, or preferably an alkylated derivative, e.g. di-n-butyl squarate, or croconic acid with electron-donor molecnles. The croconium dyes absorb at significantly longer wavelengths than the sqnarylinms as shown in Figure 4.2. 

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. °... 

Fig. 4. Dyes for WORM media (a) hydroxy squarylium (9,10) (b) SQS = squarylium core with thiopyrylium end group (11) (c) TPMP =...

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). 

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